tcl-lsp

A language server for Tcl with multi-editor support.

New here? See docs/capabilities.md for how to leverage the three capabilities — the f5-query engine, the Tcl compiler/analyser, and the BIG-IP registries — from the CLI, Python, the LSP, MCP, and the browser. Live demos: compiler explorer · command registry spec studio · BIG-IP report generator · example report.

The server is a native Rust binary (tcl-lsp-server). It speaks LSP over stdio, so it works with any LSP client. (The VS Code extension always launches the bundled tcl-lsp-server binary.)

Contents

Start here — Install · The seven you will use most · Full feature index

The language — Dialects, languages, and packages · F5 BIG-IP · Diagnostic and optimiser codes

Tools — Compiler explorer · Command registry spec studio · WASM, the bytecode VM, and eBPF · AI tooling · CLI tools · Packaging & environments

Tuning it — Suppressing diagnostics · Diagnostic prominence · Multi-file projects · Configuration

Contributing — Building and contributing · Screenshots · Licence

Install

Grab the artefact for your editor from Releases, or install the VS Code extension from the Marketplace. Nothing needs Python — the server is a self-contained native binary.

While the Rust rewrite is on the pre-release channel, install it from the rust branch and pin the current pre-release:

curl -fsSL https://raw.githubusercontent.com/bitwisecook/tcl-lsp/rust/scripts/install/install.sh \
  | TCL_LSP_VERSION=v2.1.19 sh

All editors

All editors connect to the native Rust binary tcl-lsp-server over stdio (build it with make rust-server, or cargo build -p tcl-lsp-server).

Also documented in INSTALL-editors.md:

• VS Code-compatible editors (load the same .vsix unchanged) — Cursor, Windsurf, VSCodium, code-server / Coder, GitHub Codespaces, Gitpod, and Eclipse Theia.
• Other LSP-capable editors (point a generic LSP client at the native tcl-lsp-server binary) — Vim (vim-lsp or coc.nvim), Kate, Kakoune, Notepad++, Geany, Lite XL, micro, CudaText, JupyterLab, Doom Emacs, and Spacemacs.

File types recognised: the Tcl family — .tcl, .tk, .itcl, .tm, .test, .exp, .expect, .apl, .tclspec — the F5 surfaces — .irul, .irule, .irules, .iapp, .iappimpl, .impl, .tmsh, .scf — and the EDA vendors' constraint and script suffixes — .sdc, .upf, .xdc, .qsf, .qpf, .qip, .do, .globals. Every editor's registration list is generated from one catalogue (cargo xtask gen-editor-extensions), so they never disagree.

Two further axes: whole filenames — bigip.conf and its siblings are recognised by name, since a bare .conf belongs to every unrelated config file, and a file named presentation (no extension) is APL — and shebangs, #!/usr/bin/tclsh, #!/usr/bin/wish, and #!/usr/bin/expect, where a versioned shell name (tclsh8.6, wish9.0) also pins the release. Per-file # tcl-dialect: comment directives pin a specific dialect. Every tcl CLI verb applies the same detection (directive, shebang, package require Tcl guard, content signals such as a when EVENT { handler, then extension) unless --dialect is passed — per input file for diag / lint / validate / minimize, and once for the whole invocation for the verbs that combine their inputs into one source (opt, format, minify, explore, diagram, the graph verbs, …). So the CLI and the editor report the same set, and apply the same optimisations, for the same file. Files named tclpkg.tcl are analysed as tcl pkg package manifests: their directives resolve against the manifest command set instead of drawing unknown-command warnings.

Full per-editor instructions, including every VS Code-compatible and generic LSP editor, live in INSTALL-editors.md. For the tcl and f5 command-line tools, see INSTALL-cli.md.

VS Code

Install from the Marketplace, which serves your platform's package automatically, or sideload the -universal .vsix from Releases:

code --install-extension tcl-lsp-vscode-<version>-universal.vsix

The extension bundles the native server — nothing else to install. Settings live under Settings > Extensions > Tcl.

The -universal package works on any architecture, not just the seven with a prebuilt binary: it also carries the language server as a WebAssembly (WASI) module and falls back to it when no native binary matches, offering a one-time prompt to install the WASM runtime it needs. Editors other than VS Code can take the same module — tcl-lsp-server-wasi.wasm — straight from Releases and run it under wasmtime; see INSTALL-editors.md.

Also published to Open VSX for code-server, openvscode-server, Gitpod, and Theia — see INSTALL-editors.md.

In the browser — vscode.dev and github.dev

The same extension runs in a browser extension host, with no server binary and nothing to install locally: press . on a GitHub repository, or open https://vscode.dev, and install Tcl/Tk, iRules, EDA-Tools, Expect LSP/MCP from the Extensions panel. There the language server is the same analyser compiled to WebAssembly, running in a Web Worker in the page.

What is the same: diagnostics, semantic highlighting, hover, completion, formatting, folding, optimisations, and the LSP-driven commands. What is not: anything that needs a process or a filesystem — runtime validation (tclsh), the compiler explorer, the spec studio, the Tk preview, and the Copilot chat participants stay desktop-only, and cross-file analysis is limited on a virtual workspace (see INSTALL-editors.md).

Neovim

Copy tcl_lsp.lua to ~/.config/nvim/server/ and enable it (vim.lsp.enable('tcl_lsp')) — no plugin needed on Neovim 0.11+. Point cmd at your tcl-lsp-server binary.

Zed

Command Palette > zed: extensions > search Tcl. The extension downloads the matching tcl-lsp-server release binary on first use.

Emacs

Register the server with eglot (Emacs 29+) or lsp-mode, pointing at your tcl-lsp-server binary — snippets for both are in editors/emacs/.

Helix

Add a [language-server.tcl-lsp] block naming the tcl-lsp-server binary to ~/.config/helix/languages.toml — see editors/helix/.

Sublime Text

Install TclLsp from Package Control, or drop TclLsp.sublime-package into Installed Packages/. Install the LSP package too for language-server features — the matching native server is then downloaded on first use.

JetBrains

Settings > Plugins > gear > Install Plugin from Disk…, select tcl-lsp-jetbrains-<version>.zip, restart. The plugin bundles the native server for every platform. Requires IDEA Ultimate 2024.1+ (free editions from 2025.3).

The seven you will use most

Everything below this section is available too — this is what you will actually touch on a normal day. The full feature index has the rest.

1. Diagnostics that catch real bugs

Arity errors, unknown subcommands, best-practice violations, and security issues are reported with precise ranges. Diagnostics can be suppressed inline, per-file, per-project, per-editor, or globally — see Suppressing diagnostics.

string frobulate $x          ;# W001: unknown subcommand 'frobulate'
set y [expr $a + $b]         ;# W100: unbraced expr (double-substitution risk)
eval $user_input             ;# W101: eval with substituted arguments (injection risk)
catch { error "oops" }       ;# W302: catch without a result variable

Child interpreters are modelled too: a command hidden in a safe interpreter (interp create -safe) is flagged where it can never run (W129), and an interp eval into an interpreter the file never creates is flagged before it fails at run time (W140). W129 follows the hidden command through [...] bracket-substitution indirection too — a direct nested call, {*} expansion, the package ifneeded name ver [list apply {dir {...}} $dir] deferred-command idiom, and a namespace ensemble create/configure -map redirect to a hidden target — so a hidden source reached only that way is flagged the same as a direct call, in both a one-shot lint and the live editor session. The hidden set is the one Tcl itself hides — source, load, file, exec, open, socket, cd, pwd, glob, exit, fconfigure, encoding, and unload; control-transfer commands such as break and yield stay visible and are never flagged.

interp create -safe s
interp eval s { source setup.tcl }   ;# W129: 'source' is hidden in this safe interpreter
interp eval ghost { puts hi }        ;# W140: interpreter 'ghost' is never created in this file

A direct call into one of the 11 private, undocumented ::tcl:: implementation namespaces that back a built-in ensemble command (::tcl::dict, ::tcl::string, ::tcl::array, ::tcl::file, ::tcl::info, ::tcl::clock, ::tcl::binary, ::tcl::namespace, ::tcl::encoding, ::tcl::zlib, ::tcl::chan) is flagged with a concrete suggestion for the public ensemble command instead — the call works, but the namespace is not a documented or version-stable contract. Tcl's own public, documented tcl::-rooted commands (tcl::mathop::+, tcl::mathfunc::sin, tcl::prefix) are never flagged.

::tcl::dict::create a 1              ;# W143: use 'dict create' instead

Analysis is file-aware where Tcl semantics demand it: in a pkgIndex.tcl the $dir variable the package loader injects before the index script runs is treated as already defined, so reading it is not flagged read-before-set (W210) — while the same read in an ordinary file still is.

A proc, class, rename target, or interp alias that was renamed or deleted away (rename NAME {}, an interp alias {} NAME {} deletion) with no later re-establishment under the same name draws W123 wherever it's still called — calling it fails invalid command name at runtime just like a name that was never defined. The check is call-site and conditional-body aware: a call that runs before the deletion, or a deletion recorded inside a proc/method body that might never execute, does not draw the warning.

proc helper {} { return 1 }
rename helper {}
proc caller {} { helper }      ;# W123: helper was deleted, never re-established

Diagnostics see the whole workspace, not just the open file. A call to a proc defined in a sibling file is recognised as the command it really reaches, and a call with the wrong number of arguments is reported with the same codes as a same-file one — go-to-definition and the Problems panel answer from one shared lookup, so they cannot disagree about whether a name exists. Matching is by fully-qualified name in Tcl's own resolution order, so a proc ::deep::buried never silences a bare buried call that Tcl would not route there.

# deflib.tcl
proc libtest {a b c} { return [expr {$a + $b + $c}] }

# plaincaller.tcl — no `source`, same workspace
libtest 1 2                    ;# E002: expected at least 3, got 2 (not "unknown command")

source is followed when its path resolves statically — a literal, or the common [file join [file dirname [info script]] …] form — so the sourced file's package requires and definitions carry into the sourcing file, from the source statement onward exactly as Tcl loads them.

# tkFile.tcl
package require Tk

# main.tcl
winfo exists .l                ;# W120: Tk is not loaded yet at this line
source tkFile.tcl
winfo exists .l                ;# no warning — Tk is loaded from here on

Where a fact cannot be proven the analyser says nothing rather than guessing: a source path it cannot resolve to a file in the workspace, a load, an auto_path mutation, a namespace unknown handler, a dynamic namespace import, a dynamic user proc unknown, or a source that has itself been renamed or aliased away all make the available command and package set unknowable, and W120 / W123 go quiet for that file. A false warning on working code is worse than a missing one.

The eval family (eval, uplevel, namespace eval, interp eval) is analysed the way Tcl runs it: the trailing words concatenate into one script, so a multi-word call is walked as the script it actually evaluates rather than its first word alone — no invented arity errors, and the variables it really sets count as written. A brace-quoted word is static script text even when it contains $ or [ (the braces blocked the substitution; eval resolves it when the script runs). A genuinely dynamic word (eval $cmd arg) makes the script unknowable, so the analyser claims nothing instead of guessing — and namespace inscope is honoured as the one member whose tail appends as list elements rather than joining. Everything found inside the concatenated script — definitions, references, diagnostics — is anchored at its real source bytes, so rename and go-to-definition work inside these calls.

eval set l2 hello              ;# runs 'set l2 hello' — no wrong-#-args, l2 is set
eval {set l2} {$value}         ;# same script; $value resolves when it runs
namespace eval ::cfg set port 8080   ;# ::cfg::port is really written

Object typing follows commands through rename and interp alias chains: a class constructor reached under a renamed or aliased name still types the object it builds, so method validation (W308) names the real class instead of degrading into untyped-dispatch noise — while a constructor called before the rename/alias exists, an alias with bound extra words, or an alias landing on a vacated name stays untyped, just as it fails in tclsh.

oo::class create Dog { method bark {} { return woof } }
rename Dog Cat
interp alias {} Pup {} Cat
set d [Pup new]
$d fly                         ;# W308: unknown method 'fly' on ::Dog

The named-object construction form (ClassName create objName, as opposed to set d [ClassName new]) resolves identically — hover, completion, go-to-definition, references, and W308 all treat ClassName create obj; obj method and set o [ClassName new]; $o method the same way, including when ClassName is a class factory reached through a renamed metaclass command:

oo::class create C { method mrun {} { return 1 } }
C create obj
obj nosuchmethod                ;# W308: unknown method 'nosuchmethod' on class '::C'

oo::class create ::R::M { superclass oo::class }
rename ::R::M ::R::Mk
::R::Mk create ::R::W { method go {} { return went } }  ;# ::R::W is a real class

The grammar of a command follows its binding too. A statically visible namespace import, interp alias, rename, or a top-level proc that shadows a built-in re-points every registry-driven feature — highlighting, format-specifier hints, folding, formatting, minifying, go-to-declaration, the call graph, parameter-usage inference, and the iRules object-reference scan — at the command a head really names. Formatting is the visible one: a body-bearing command reached through a proven alias is expanded onto its own lines, and one whose name has been renamed away or taken over by a user proc is left exactly as written. Chains compose (interp alias {} a {} format; rename a b leaves b naming format), and the explicitly global spelling behaves identically to the bare one. Anything unprovable — a computed binding, an alias with pre-bound arguments, another interpreter's command table, a binding nested inside a body — abstains rather than guessing. See the KCS note.

rename if maybe
maybe {$x} {puts a}            ;# left as written — `maybe` is not `if`'s grammar
interp alias {} guard {} if
guard {$x} {puts a}            ;# expanded like `if`, because it is `if`

W113 ("proc shadows a built-in") only fires for a genuine core built-in. A proc named after a command that is gated behind package require — a tcllib package, argparse, an itcl/TclOO helper, … — is not flagged: that command does not exist until its package is loaded, and even then a proc of the same name is that package's own implementation, not a shadow of a core built-in. The one exception is a package a dialect profile ships ambiently (an F5 command pack, an EDA vendor tool surface) — that command is the profile's genuine, always-present surface, so redefining it still warns.

package require argparse
proc ::argparse {args} { ... }   ;# no W113: argparse is package-gated, not a core built-in
proc ::set {a b} { ... }         ;# W113: 'set' is a genuine core built-in

What the analyser checks

Seven families of finding, each code with its own page explaining why the check exists, a triggering example, and the fix:

Full tables: diagnostic codes · optimiser codes · per-code pages.

2. Dialect-aware semantic highlighting

Variables, procs, keywords, and strings are classified using SSA-informed type information, giving richer highlighting than a TextMate grammar alone. The server provides 44 token types beyond the standard LSP set, including sub-token highlighting inside strings. Tokens are cached per top-level chunk so only dirty regions are recomputed after an edit, and the server supports textDocument/semanticTokens/full/delta for bandwidth-efficient incremental updates.

Token requests are prioritised over deeper analysis: a large or freshly opened file serves an immediate baseline response instead of waiting behind a full analysis pass, then the server pushes a refresh once the fully analysis-enriched tokens (regex-aware retagging, resolved object-method dispatch) are ready — so highlighting never stalls waiting on the analyser, only briefly starts coarser on a cold file.

namespace eval app {
    variable count 0            ;# 'count' highlighted as variable
    proc handle {request} {     ;# 'handle' highlighted as function
        incr count              ;# 'incr' highlighted as keyword
        puts "req: $request"    ;# '$request' highlighted as variable inside string
    }
}

In addition to standard token types (keyword, function, variable, string, comment, number, operator, parameter, namespace), the server provides domain-specific token types:

Command options are highlighted precisely for commands the registry knows, including object methods on a tracked handle — the standard TclOO / Tk pattern set chart [ticklecharts::chart new]; $chart Xaxis -name x -type value resolves Xaxis's options through the registry. Any other -option value pair on an unknown command head is highlighted by shape, while negative numbers (-5), special floats (-inf), substitutions (-$var), and the -- end-of-options marker are handled per Tcl's conventions.

A Tk/ttk widget's own instance command resolves the same way, keyed on the widget path rather than an object handle: ttk::treeview .t then .t instate {selected} { … } / .t tag configure hidden -foreground grey, or set lb [listbox .l]; $lb curselection, get precise subcommand, option, and arg-value highlighting, hover, and completion, plus unknown-subcommand (W001) and arity (E002/E003) diagnostics — for both the bareword form and a variable holding the constructor's return value.

Script-body arguments are highlighted as scripts, not opaque strings. The body of an apply {argList body} lambda literal has its commands, variables, and strings tokenised like any other body, and the argument list names — a braced {a b} list or a bare single name (apply {dir { … }}) — are painted as parameter declarations. This reaches apply reached indirectly through [list apply {argList body} $val] too — the idiomatic way to build a deferred command around a dynamic value, most commonly a pkgIndex.tcl entry: package ifneeded myPackage 1.0 [list apply {dir { source [file join $dir init.tcl] }} $dir] highlights source/file/join inside the lambda body correctly, not as one opaque string. package ifneeded's deferred script argument is recognised as a script body in its own right too, whether literal or list-quoted.

3. Completions

Context-aware completions for commands, subcommands, variables, proc names (workspace-wide), switch arms, and package require names. When a fragment of two or more characters matches nothing by prefix, completion falls back to fuzzy matching, so a typo still finds the intended name (prefix matches always keep their exact list).

string len|              ;# offers: length, last, ...
set name "world"
puts $na|                ;# offers: $name
dict |                   ;# offers: create, get, set, exists, ...
lsaerch|                 ;# fuzzy fallback offers: lsearch

Signature help

As you type arguments, the server shows the expected parameter list with the active parameter highlighted.

proc connect {host port {timeout 30}} { ... }
connect "db.local" |
#                  ↑ signature help shows: connect (host port ?timeout?)
#                    with 'port' highlighted as the active parameter

4. Hover documentation

Hovering on a command, proc call, variable, or operator shows its signature, doc comment, and type information. Multi-line docstrings are supported, and @param, @return, and @brief tags are parsed and displayed as structured markdown. Docstrings can appear above the proc or inside the proc body.

# @brief Greet a person by name.
# @param name - Who to greet
# @return The greeting string
proc greet {name} {
    return "Hello, $name!"
}

greet "Alice"     ;# hover on 'greet' shows signature + formatted @param/@return docs

5. Navigation: definition, references, call hierarchy

Jump to the definition of a proc or variable — works across files in the workspace.

proc helper {} { return 42 }
set x [helper]       ;# Ctrl+Click on 'helper' → jumps to proc definition above
puts $x              ;# Ctrl+Click on '$x' → jumps to the set statement

Find references

Locate every usage of a proc or variable, including inside nested braced script bodies such as if, foreach, and namespace eval.

proc add {a b} { expr {$a + $b} }
set sum [add 1 2]       ;# ← reference to 'add'
puts [add 3 4]           ;# ← reference to 'add'
# "Find all references" on 'add' highlights all three locations

References follow TclOO dispatch, too. A method is found through every $obj method call on a tracked instance, every intra-class my method dispatch, and next / nextto super-dispatch — including calls nested in a […] substitution, embedded in a quoted / compound word, or nested inside if / while / foreach / switch / try / catch / eval / dict for (any combination, arbitrarily deep). A classmethod dispatches on the class's own command rather than an instance, so it is found through every bare ClassName method call, including from a subclass's own command when the subclass inherits (does not override) the classmethod. A property (oo::configurable's property name -get {...} -set {...} form) is found through every my <property> dispatch inside the class body — properties have no $obj property dispatch shape or inheritance model, so this is a class-local scan. Expr math functions resolve to their backing proc, so a proc ::tcl::mathfunc::foo is found (and renamed) from every foo(...) used inside expr — symmetrically, whether the query starts at the declaration or at a call site, and honouring C Tcl's caller-namespace-first dispatch (a proc in ::ns::tcl::mathfunc wins inside ::ns, and an unrelated global proc foo never does). Conversely, a proc that lives only in a tcl::mathfunc namespace is not reachable as a bare command — real Tcl raises invalid command name — so a bare call to it resolves to nothing.

Hover and completion read the same registry data. Hovering a bare sin(1.0) inside expr shows what ::tcl::mathfunc::sin shows, a user override shows the overriding proc, and completing inside any expression argument (expr, an if / while condition, a for test — whichever arguments the command registry marks as expressions) offers the math functions your Tcl version has, under their bare names.

A constructor or destructor is invoked positionally (ClassName new/create/destroy), never dispatched by name, so it has no general reference story the way a method does — but an overriding subclass's own constructor/destructor chaining up to it via next / nextto is still a name-independent reference, and code lens / find references surface it, resolved through the full class hierarchy (skipping an intermediate ancestor that declares no constructor/destructor of its own).

A class is found through every use of its name, not only <Class> new. A superclass, mixin, or [incr Tcl] inherit argument that names the class is a reference to it — resolved by the referencing class's namespace, so a fully-qualified superclass ::ns::Base in one file is found (and renamed) from ::ns::Base's declaration in another, while a same-named class in an unrelated namespace is never cross-linked. Renaming a class therefore rewrites every superclass / mixin / inherit site, keeping the inheritance graph intact.

oo::class create Store {
    method get {key} { return [my lookup $key] }   ;# ← 'lookup' reference (my dispatch)
    method lookup {key} { return $key }
}
set s [Store new]
puts "value: [$s get k]"                            ;# ← 'get' reference (in a quoted word)

Call hierarchy

Inspect incoming callers and outgoing callees for any procedure.

proc validate {input} { return [string is integer $input] }
proc process {data}   { if {[validate $data]} { store $data } }
proc main {}          { process "42" }

# Incoming calls to 'validate': process
# Outgoing calls from 'process': validate, store

source links, including computed paths

Every source argument the server can place becomes a clickable link, and the same resolved path drives navigation, cross-file diagnostics and load order — so a file reached through a computed path behaves exactly like one named literally.

source lib/util.tcl                                    ;# literal
source [file join [file dirname [info script]] x.tcl]  ;# [info script] idiom

set dir [file dirname [info script]]
set src [file join $dir src]
source [file join $src parser.tcl]                     ;# chained constants

namespace eval ::snit:: {
    variable library [file dirname [info script]]
}
source [file join $::snit::library main1.tcl]          ;# namespace variable

A variable another file assigns resolves too, when every file that sources this one agrees on its value before sourcing (the OSVVM ${::osvvm::OsvvmScriptDirectory}/… shape). A path the server cannot prove — built from $argv, from a write guarded by if {![info exists …]}, or from routes that disagree — produces no link rather than a guessed one.

The link is offered on the file name itself, never across the surrounding substitution, so [file join …] keeps its normal syntax colouring.

6. Quick fixes and refactorings

Quick-fix actions are offered for diagnostics that have automated repairs. Refactoring actions are available on selected code.

expr $a + $b         ;# W100 → quick-fix: wrap in braces → expr {$a + $b}
catch { error "x" }  ;# W302 → quick-fix: add result variable → catch { error "x" } result
set x [expr {$x+1}]  ;# O114 → quick-fix: use incr idiom → incr x

Extract to proc — select one or more lines, trigger code actions (Ctrl+.), and choose Extract selection into proc. The selected code moves into a new proc with detected variable parameters; the original lines are replaced with a call. The editor places the cursor on the new proc name so you can rename it immediately.

Inline proc — put the cursor on a call to a single-command proc, trigger code actions (Ctrl+.), and choose Inline proc to replace the call with the proc's body. Branchy bodies are declined, as is any call whose head is frame-sensitive — a command that terminates a block, transfers control, creates a scope alias, or creates a barrier (return, break, continue, tailcall, yield, uplevel, upvar, global, variable, source, exit, …) — because lifting one of those out of its proc frame changes what it returns from, breaks out of, or binds against.

Rename symbol

Safely rename a proc or variable across all scopes in the file.

proc greeting {name} {
    puts "Hi, $name"
}
greeting "World"
# Rename 'greeting' → 'salute' updates the proc definition and all call sites

A command name held in a variable follows the rename through its defining constant — the literal is rewritten, never the $cmd head — so the dispatch keeps working, and both arms of a conditional assignment keep their own targets:

proc target {} { return hi }
set cmd target
$cmd
# Rename 'target' → 'renamed' also rewrites `set cmd target`, so `$cmd`
# still dispatches; the `$cmd` word itself is never touched.

When a contributing constant has no exact source spelling to rewrite, the rename is refused outright rather than left half-applied, and a file sourced under several namespaces renames every namespace's call sites together. TclOO navigation honours the real dispatch: go-to-definition on $obj method lands on the implementation the call actually enters (mixins ahead of the class, subclass overrides ahead of bases), an externally unexported method resolves nowhere (as in C Tcl), and per-object oo::objdefine methods resolve per receiver binding, so same-named locals in different procs never collide.

Namespace variables navigate across files too. $::tomato::version jumps to — and hovers, and finds references for — the variable version inside whichever file's namespace eval tomato { … } declares it, in either direction. Only qualified occurrences take part: a bare $v names whatever the surrounding scope supplies, which is a within-file question, so it is never widened to a same-named variable somewhere else in the workspace.

Namespace names navigate too. The ::tomato of namespace children ::tomato, namespace exists, namespace delete, namespace upvar, or a second namespace eval ::tomato { … } block jumps to — and hovers, and finds references for — every namespace eval block that declares it, wherever those live, since reopening a namespace extends the same one. A relative name resolves against the namespace it is written in, exactly as Tcl does. Words that only look like namespace names are left alone: namespace tail / qualifiers take arbitrary strings, import / export / forget take glob patterns, and origin / which name commands. A namespace whose name also happens to be a command's never resolves to that command — the two are different kinds of symbol — and renaming a namespace is refused with a reason rather than quietly renaming the command instead.

7. Formatting

Full-document and range formatting with 25 configurable options. Defaults follow the F5 iRules Style Guide. Supports full-document (textDocument/formatting) and range (textDocument/rangeFormatting) requests.

# Before:
proc messy { x  }  {
if {$x>0}{return $x }
   set y   [expr $x+1]  ;  puts $y }

# After (formatted):
proc messy {x} {
    if {$x > 0} {
        return $x
    }
    set y [expr $x + 1]
    puts $y
}

Capabilities include indentation (spaces or tabs, configurable size), brace placement (K&R), expression bracing enforcement, variable bracing ($var → ${var}), keyword-abbreviation expansion, boolean-form normalisation, line-length wrapping, semicolon splitting, single-line body expansion, blank-line normalisation between procs and blocks, comment alignment, trailing whitespace trimming, and line-ending normalisation (LF/CRLF/CR).

# Expression bracing enforcement (enforceBracedExpr = true):
if {$x > 0} { ... }       ;# ✓ braced
if $x>0 { ... }           ;# → rewritten to: if {$x > 0} { ... }

# Variable bracing (enforceBracedVariables = true):
puts $name                 ;# → rewritten to: puts ${name}

# Keyword-abbreviation expansion (expandAbbreviations = true, the default):
string le $s               ;# → rewritten to: string length $s
lsearch -noc $x $p         ;# → rewritten to: lsearch -nocase $x $p
string l $s                ;# ✗ ambiguous — left alone, and reported as W145

Full feature index

Every feature has a KCS note: what it does, how to use it, and its settings.

Reading and navigating code

Diagnostics and analysis

Changing code

Dialects, packages, and environments

Compiler, VM, and tooling

AI tooling

F5-specific features — the BIG-IP object model, f5 query, the report generator, iRules analysis and testing, iApps/APL, XC translation — are indexed in README-f5.md.

The whole set is also browsable in-editor and from the CLI: tcl help <feature>, the MCP help tool, and the VS Code /help chat command all read these same notes.

Dialects, languages, and packages

Every supported dialect

Eighteen dialect profiles, each gating which commands exist, which are deprecated, and which options and subcommands are valid. The list below mirrors the profile catalog (DialectProfile) in rust/tcl-dialect, the single source of truth — its display_name is the second column.

Pick one per file with a # tcl-dialect: comment, per project in configuration, or let detection choose — see Automatic dialect detection below.

Every package in the registry

Commands from these 69 packages are modelled with hover docs, completion, arity checking, argument roles, and side-effect classification. They activate when their package require appears (or ambiently, when a dialect ships them):

argparse, base32::core, base64, bibtex, cksum, cmdline, comm, control, cookiejar, crc16, crc32, csv, debug, defer, dns, f5-irules-cmds, fileutil, generator, hook, html, http, inifile, ip, Itcl, json, lambda, logger, math, math::constants, math::statistics, md4, md5, md5crypt, mime, msgcat, namespacex, ooutil, opt, otp, platform, platform::shell, processman, rc4, report, safe, sha1, sha2, smtp, snit, soundex, stooop, stringprep, struct::list, struct::queue, struct::set, struct::stack, sum, tcl::chan::halfpipe, tcl::idna, tcltest, textutil, ticklecharts, tie, Tk, unicode, uri, uuid, websocket, yaml

That includes Tk in full, Itcl, and the whole tcltest surface with per-version availability (test -errorCode only from tcltest 2.5, bytestring gone under Tcl 9.0). Most of the rest is tcllib — see tcllib package coverage for the module-by-module state, and kcs-howto-add-command-registry-package.md to add another.

Third-party and in-house commands that are not in the registry can be declared with stub annotations.

Dialect profiles

Switch between Tcl 8.4/8.5/8.6/9.0/9.1, F5 iRules, F5 iApps, F5 tmsh, and EDA tooling profiles. Tk, tcllib, and stdlib commands activate automatically when their package require appears — including the full tcltest surface (test, configure, and the convenience commands) with per-version awareness, so test -errorCode is offered only for tcltest 2.5+ and bytestring disappears under Tcl 9.0. F5 iRules metadata follows BIG-IP command/event source data, including profile aliases used by newer namespaces and events, shared TLS helper profiles such as PERSIST, and protocol namespace layer metadata that stays aligned with the enabling profile stack. The configured BIG-IP target also gates subcommands and their enumerated modes: for example, SSL::c3d cert_lifespan, SSL::c3d cert_start_date, and persist mcp are offered only for BIG-IP 21.1+.

# With dialect = tcl8.6:
try {
    open $path r         ;# ✓ known in 8.6
} on error {msg} {
    puts $msg
}

# With dialect = tcl8.5:
try { ... }              ;# W002: command disabled in active dialect (try requires 8.6)

The ::tcl:: namespace itself is a Tcl 8.5+ addition — plain tcl8.4 and F5 iRules (a real embedded Tcl 8.4.6) have no such namespace at all, so its contents are gated to their real introduction release:

# With dialect = tcl8.4 (or f5-irules):
::tcl::mathop::+ 1 2               ;# W002: disabled in active dialect (::tcl:: is 8.5+)
tcl::build-info version             ;# W002: disabled in active dialect (available in: tcl9.0, tcl9.1)
tcl::tm::path add /some/dir         ;# W002: disabled in active dialect (available in: tcl8.5, tcl8.6, tcl9.0, tcl9.1)

Individual tcl::mathop operators can be gated even more precisely than the namespace itself: lt/le/gt/ge (TIP 461) need Tcl 9.0, one release newer than the ::tcl:: namespace's own 8.5 baseline:

# With dialect = tcl8.6:
::tcl::mathop::lt 1 2              ;# W002: disabled in active dialect (available in: tcl9.0, tcl9.1)

The server ships a registry of command signatures, argument roles, and validation rules keyed by dialect. Switching the dialect profile changes which commands are known, which are deprecated, and which event/layer constraints apply.

Version-aware diagnostics reach every gateable level of a call, not just the command: a subcommand, a second-level operation of a two-level ensemble (info object class), an option, and a literal argument value — each independently reports "not introduced yet" (W135/W136), "deprecated" (W144), or "removed" (W139) against the resolved version floor. A package require Foo A-B range whose upper bound reaches past a retirement is caught too: the floor alone can be satisfied while part of the accepted range is not, so W139 fires with a hedged "not available in every version satisfying requirement A-B" message rather than staying silent.

Automatic dialect detection

The dialect is selected automatically using the following priority chain (highest to lowest):

1. Editor language ID -- opening a file as tcl-irule, tcl84, etc. selects the matching dialect immediately. (The version-pinned VS Code language ids are undotted -- tcl84, tcl85, tcl86, tcl90, tcl91 -- because VS Code cannot carry a configurationDefaults override for a language id containing a .. The dialect names below keep their dots, and the server still accepts the dotted tcl8.4-style id other editors send.)

2. File extension -- each profile in the catalog owns its extensions: .irul/.irule/.irules → f5-irules, .iapp/.iappimpl/.impl → f5-iapps, .tmsh → f5-tmsh, .scf → f5-bigip, .exp/.expect → expect, .tclspec → spectcl, .globals → cadence-eda-tcl, .qsf/.qpf/.qip → intel-quartus-eda-tcl, .do → mentor-eda-tcl, .sdc/.upf → synopsys-eda-tcl, .xdc → xilinx-eda-tcl. A SpecTcl pack can route further extensions to a dialect with a file_extension row, so a private library's own suffix opens in the dialect it is written for.

3. Comment directive -- a # tcl-dialect: <dialect> comment in the first 5 lines of a file pins the dialect for that file:

   # tcl-dialect: tcl8.4
   set x 1
   

4. Shebang -- #!/usr/bin/env tclsh8.5 selects tcl8.5; #!/usr/bin/expect selects expect.

5. User setting -- the tclLsp.dialect configuration value acts as the default for files that have no per-file hint.

6. Hardcoded fallback -- tcl8.6 when nothing else matches.

Per-file hints (directive, shebang, extension) always take priority over the global setting, so different files in the same workspace can target different Tcl versions without manual switching.

Tk, tcllib, and Tcl stdlib commands are automatically recognised when the corresponding package require appears in the file. No manual toggle is needed — the registry activates the relevant command definitions per-document. The tcllib coverage spans the cryptography/hash (md4, ripemd, crc*, aes/blowfish/des, …), encoding (base32, ascii85, uuencode, yencode), maths (math, math::fuzzy, math::roman), data/utility (inifile, units, counter, tie, lambda), web/protocol/client (asn, ncgi, imap4, ldap, ftp, pop3, irc, rest, SASL, websocket, …), format (png, jpeg, tiff, gpx, mapproj, nmea), and ensemble (generator, debug, hook) package families — see the tcllib coverage note.

Dialect command stubs

For commands that the LSP does not know about (custom extensions, vendor tools, internal frameworks), you can declare stubs so the LSP understands their signatures. Two mechanisms are supported:

External stub files (<name>.tcl.stubs):

# synopsys.tcl.stubs
stub foreach_in_collection {varName:var collection body:body} -loop
stub get_cells {?-hierarchical? ?-filter? pattern:pattern} -pure
stub sizeof_collection {collection} -pure
stub expr-func sizeof 1

Inline stubs (in any .tcl file, using markers):

# tcl-lsp: stubs-begin
# tcl-lsp: stub foreach_in_collection {varName:var collection body:body} -loop
# tcl-lsp: stub get_cells {pattern:pattern} -pure
# tcl-lsp: stub expr-func sizeof 1
# tcl-lsp: stub expr-op contains 2
# tcl-lsp: stubs-end

Multiple stubs blocks per file are supported. Argument roles include body, expr, var, var_read, name, pattern, channel, and value (default). Flags include -barrier, -loop, -pure, -mutator, -unsafe, and -scope_alias.

Expression stubs declare custom math functions (expr-func) and infix operators (expr-op) with optional arity.

See KCS: Dialect stubs for full syntax.

Command alias resolution

When interp alias {} name {} target ?args? creates a command alias in the current interpreter, the LSP automatically inherits the target command's argument semantics. This means expression arguments, body arguments, variable names, and patterns are all correctly analysed through the alias:

interp alias {} = {} expr
proc calculate {x y} {
    set result [= {$x + $y}]   ;# $x and $y recognised as reads — no W214
    return $result
}

Alias information is also used by LSP features: hover shows the target command's documentation, completion offers aliases as candidates, go-to-definition follows aliases to the target proc, and signature help shows the target's parameter hints.

See KCS: Command alias resolution for details.

Proc argument trait inference

The analyser automatically infers how each proc parameter is used inside the proc body, producing structured trait annotations:

Two analysis tiers: a fast shallow pass (synchronous, top-level commands) and a deep pass (asynchronous, recursive descent into nested bodies). Traits feed optimisation, shimmer analysis, taint propagation, and diagnostics.

See KCS: Proc arg traits for details.

F5 BIG-IP

F5 support is a first-class part of tcl-lsp, and large enough to have its own document: README-f5.md.

It covers the f5-irules, f5-iapps, f5-bigip, and f5-tmsh dialects; the BIG-IP configuration model and iRule extraction; the f5 CLI (query, cleanup, grep, irule, report); the jq-shaped query DSL and its Python (f5q) bindings; the standalone HTML report generator; iRules-to-XC translation; and the iRule Event Orchestrator test framework with fakeCMP multi-TMM simulation.

Compiler explorer

Compiler explorer (VS Code panel)

An interactive webview panel (Ctrl+Alt+E / Cmd+Alt+E) that visualises the compiler's intermediate representation, control-flow graph, SSA form, optimiser output, Tcl bytecode, and WebAssembly disassembly for the active editor. The WASM tab renders each instruction with its originating Tcl source range (click an instruction to place the source cursor inside the expression, substituted command, or post-; sub-command it compiled from), resolved call targets (click call 42 ; ::greet to jump to both the callee's disassembly and its definition), resolved branch targets (click br 0 ; loop_header foreach to jump to the matching loop open), a labelled block / loop / if for each Tcl construct (foreach, while, for, if, catch body, switch arm), a source-line comment above every instruction group, and orthogonal control-flow arrows in the left gutter.

The Interproc tab opens with a unit scope card: which registry-declared boundaries the file crosses (package provide, source, namespace export, …), whether the analysis had a cross-file view of the workspace, the per-argument verdict behind every interprocedural constant fold, and the param constants each procedure was actually analysed under. That last line is the direct answer to "why did this condition fold?" — and, by its absence, to "why didn't it?". It is the first place to look when a constant fold — or its absence — is a surprise; the same data is the unitScope view in the tcl explore CLI and TUI.

The IR, CFG, SSA, bytecode, and WASM tabs each carry an optimiser lens (off / on / diff). The diff mode compares the relevant node — IR statement, CFG block, or bytecode instruction — rather than raw text, so byte offsets, source ranges, sequence indices, and tree-connector glyphs that merely shift when the optimiser adds or removes a node are ignored. A single rewrite then shows as a single localised change instead of every following line being flagged. The tcl-explorer CLI and TUI render the same offset-free diff via --opt diff.

┌─────────────────────────────────────────────────┐
│  IR  │  CFG  │  SSA  │  Optimiser  │  Bytecode  │
├─────────────────────────────────────────────────┤
│  proc fibonacci {n}                             │
│    ENTRY:                                       │
│      %0 = param n                               │
│      %1 = const 0        ;  set a 0             │
│      %2 = const 1        ;  set b 1             │
│    LOOP:                                        │
│      %3 = phi [%1, ENTRY] [%6, BODY]            │
│      ...                                        │
└─────────────────────────────────────────────────┘

Compiler explorer (CLI)

Console tool for inspecting the compiler pipeline: IR, CFG, SSA, optimiser rewrites, shimmer warnings, taint analysis, and bytecode.

# Full exploration of a Tcl file
tcl explore script.tcl

# Focus on optimiser rewrites only
tcl explore script.tcl --show opt

# Inline source with optimised output
tcl explore --source 'set a 1; set b [expr {$a + 2}]' --show-optimised-source

# Show only IR and CFG
tcl explore script.tcl --show ir,cfg

# iRules dialect with flow analysis
tcl explore irule.tcl --dialect bigip --show irules

# Serve the embedded web GUI
tcl explore --serve

Available views: ir, cfg, ssa, interproc, types, opt, gvn, shimmer, taint, irules, callouts, asm, wasm. Groups: all, compiler, optimiser.

Compiler explorer (web GUI)

The embedded web UI for the compiler explorer is served by the native tcl binary via tcl explore --serve. The same Rust → WebAssembly module (make explorer-wasm) is bundled into the VS Code and JetBrains panels, which compile in the webview itself — offline, with no LSP roundtrip.

# Serve the embedded web GUI
tcl explore --serve

# Choose a port
tcl explore --serve --port 8080

Command registry spec studio

A web page for exploring the command registry: browse every command tcl-lsp knows for a chosen dialect, edit any field of its CommandSpec, and render the result back out as a drop-in registry .rs module (copyright banner included) or a Tcl dialect stub. Live at bitwisecook.github.io/tcl-lsp/spec-studio, or build it locally with make spec-studio-wasm.

The form is generated from a schema the registry itself reports, so it covers every field of CommandSpec and SubCommand — a field added to the registry appears in the studio without a front-end change, and a drift test fails if one is ever missed.

Import a package takes a package's own .tcl files, runs the real analyser over them, and infers a starting spec for each proc it finds: arity from the parameter list, argument roles and traits from how each parameter is used in the body (evaluated as a script, upvar'd and written, iterated as a list), hover text from the doc comment, and a package require gate from package provide. Every guess is listed with the evidence behind it.

Import several releases instead of one — a .zip per release, uploaded or fetched from GitHub — and it derives each command's version range from what the releases actually witness: introduced_version from the first release the command appears in, retired_version from the first it is gone from, with the reasoning shown beside every bound. The same derivation backs tcl spec import on the command line.

Browse the list to pick a command, or type a name you already know and press Load (Enter works too, and the box suggests matching names as you type).

The Pack DSL tab holds a SpecTcl pack's .tclspec source directly as its own authoritative document — edit the form and the text follows, edit the text and the form follows. It is a Monaco editor driven by the actual Tcl language server, compiled to WebAssembly and running in a Web Worker in your browser: the same server binary your editor talks to, so the semantic colouring, hovers, completions, diagnostics, and formatting are the ones your editor shows, not an approximation of them. The Test tab's Tcl sample gets the same editor, opened under whichever dialect you have selected. If the server cannot start the page says so and falls back to a plain text editor with the pack's own highlighting.

It works on a phone as well as a desktop: the toolbar unwraps to full-width controls, the tab strip scrolls sideways, and touch targets meet the 44px minimum. On a narrow screen the command list moves below the editor, which is why loading by name matters there.

The registry, the compiler's analyser, both renderers, and the language server are all compiled to WebAssembly and served from the page's own directory. Its content security policy lets the page reach exactly two outside hosts, api.github.com and codeload.github.com, and one clearly-labelled opt-in panel is the only thing that can use them — the release fetcher above, which acts only when you fill it in and press the button, and which has an offline .zip upload path that does the same job. Nothing else you type or import can leave your browser. Copy the output, download it, or open a pre-filled GitHub issue proposing the spec.

Compiling Tcl: WASM, the bytecode VM, and eBPF

The compiler front end is shared by the language server and by three back ends.

Tcl-to-WASM compiler

Compile Tcl scripts to WebAssembly (WAT text or binary WASM format) with the tcl compwasm verb.

# Compile to WASM binary (+ optional WAT sidecar)
tcl compwasm script.tcl -o out.wasm --wat-output out.wat

# Compile inline source
tcl compwasm --source 'set x [expr {1+2}]' -o out.wasm

Tcl VM

A bytecode interpreter that compiles and executes Tcl scripts using the compiler pipeline, with an interactive REPL and disassembly mode. Supports TclOO classes (constructors, destructors, methods, mixins, filters, private variables), namespaces, coroutine-free control flow, and 85% conformance against Tcl 9.0.3 native test suites.

The VM ships as the native tclvm binary.

# Execute a script (trailing args become the script's argv)
tclvm script.tcl arg1 arg2

# Interactive REPL
tclvm

# Inline evaluation
tclvm -c 'puts [expr {6 * 7}]'

# Show bytecode disassembly without executing
tcl dis script.tcl

eBPF (BPF-Tcl)

A low-level packet-matching language that compiles Tcl-shaped source to eBPF — see kcs-feature-bpf-tcl.md.

Tcl debugger

An interactive debugger that can single-step through Tcl scripts with breakpoints, variable inspection, and call stack visualisation, driven by the project's own bytecode VM. It ships as the native tcl-debug binary.

# Debug a script (interactive CLI)
tcl-debug script.tcl

# Speak the Debug Adapter Protocol over stdio (for an editor)
tcl-debug --dap

Debugger commands: run, step/s, next/n, finish, continue/c, break <line>/b, delete <id>/d, vars, print <var>/p, stack, list/l, quit/q.

AI tooling

Chat participants (VS Code + GitHub Copilot)

Three chat participants integrate with GitHub Copilot to provide domain-specific AI assistance backed by the LSP's static analysis.

@tcl — Tcl assistant

User:   @tcl /explain what does the fibonacci proc do?
Copilot: walks through the loop, variable assignments, and return value

@tk — Tk GUI assistant

User:   @tk /create a simple calculator with number buttons and a display
Copilot: generates Tk code with grid layout, button callbacks, and display label

Claude Code skills

Twenty purpose-built skills for Claude Code (CLI) that combine LSP static analysis with AI reasoning. The skills are native — each calls the tcl-mcp MCP server's tools, iterates on diagnostics, and produces clean output.

# Example: fix all issues in an iRule
claude /irule-fix my_irule.tcl

# Example: security review
claude /irule-review production_rule.tcl

# Example: generate a Mermaid diagram
claude /irule-diagram complex_rule.tcl

MCP server (Claude Desktop / AI agents)

A Model Context Protocol server that exposes tcl-lsp analysis to any MCP-compatible client (Claude Code, Claude Desktop, Codex, custom agents).

The server is the native Rust tcl-mcp binary — a single self-contained executable that calls the Rust analysis crates directly (no Python, no PyO3). It hosts the full tool surface (46 tools: analysis, LSP features, refactors, diagnostics, docstrings, iRule/BIG-IP tools, XC translation, Tk layout, test generation, …). Build it with make rust-mcp.

Install / register. The installer fetches the prebuilt native binary for your platform from the GitHub release (tcl-mcp-<triple>), verifies its checksum, detects supported AI harnesses, and asks separately whether to register each one. If the current project contains that harness's files, the installer offers project or user scope; otherwise it uses user scope. Claude Code, Codex, Gemini CLI, GitHub Copilot CLI, OpenCode, Hermes, Goose, and Bobbit are recognised (Bobbit supports project scope only):

./scripts/install/install.sh            # fetches + registers the native binary

• TCL_LSP_MCP_BIN=/path/to/tcl-mcp ./scripts/install/install.sh — register a local build instead of downloading.

Working inside this repo, compatible harnesses auto-discover the server via the committed .mcp.json, which launches scripts/tcl-mcp: it prefers a local build (make rust-mcp), else a cached binary, else fetches the release asset for the host platform, else builds from source. Register globally without the installer with make rust-mcp && claude mcp add tcl-lsp -- "$(pwd)/target/release/tcl-mcp".

// Claude Desktop — claude_desktop_config.json (native binary)
{
  "mcpServers": {
    "tcl-lsp": {
      "command": "/absolute/path/to/target/release/tcl-mcp"
    }
  }
}

The iRules-specific assistant (@irule) and the F5 skills are documented in README-f5.md.

CLI tools

All CLI tools are distributed as native binaries (tcl, f5-query) — no runtime required.

Unified Tcl tool (tcl)

A single verb-based CLI that aggregates common local workflows:

• opt / optimise — optimise combined input source and emit rewritten Tcl
• diag — run diagnostics across files/directories/packages
• lint — run lint diagnostics across files/directories/packages
• validate — error-level validation checks
• format — format source using canonical Tcl style rules
• symbols — emit symbol definitions for the resolved source
• diagram — extract control-flow diagram data from compiler IR
• callgraph — build procedure call graph data
• symbolgraph — build symbol relationship graph data
• dataflow — build taint/effect data-flow graph data
• command-info — look up command registry metadata
• find-legacy — detect legacy modernisation patterns (detection only)
• dis — bytecode disassembly
• compwasm — compile input to a WASM binary
• highlight — emit syntax-highlighted source (ansi or html)
• diff — compare two sources across AST/IR/CFG compiler representations
• explore — run compiler-explorer views (ir, cfg, ssa, opt, asm, wasm, ...)
• help — search bundled KCS feature docs from the SQLite help index
• pkg — package management: init, add, remove, install, list, tree, verify, info, search, update, sync, outdated, why, vendor, run
• venv — virtual environments: create, delete, info, activate, deactivate, list, update, run
• spec — author SpecTcl (.tclspec) command packs: import derives introduced_version/retired_version ranges for a package's commands from several labelled release snapshots

# Optimise everything under src/ into one output script
tcl opt src/ -o build/optimised.tcl

# Run diagnostics across a directory and a Tcl package
tcl diag src/ mypkg --package-path ./vendor/tcl

# Run lint diagnostics (same checks as `diag`)
tcl lint src/ mypkg --package-path ./vendor/tcl

# Validate syntax/error diagnostics
tcl validate src/

# Validate as JSON
tcl validate src/ --json

# Format source text
tcl format script.tcl -o formatted.tcl

# Minify source (strip comments, collapse whitespace, join commands;
# semantics-preserving — never renames symbols or adds variables)
tcl minify script.tcl -o minified.tcl

# Compact minify (also renames proc-local variables; proc names and
# global variables are renamed only with --isolated, since they are
# observable public identities — see docs/kcs/features/kcs-feature-minifier.md)
tcl minify --compact script.tcl -o minified.tcl --symbol-map map.txt

# Aggressive minify (optimise + static substring folding via SCCP + name
# compaction + alias preambles; NOT frame-transparent — it introduces
# helper variables visible to `info vars` and traces)
tcl minify --aggressive script.tcl -o minified.tcl --symbol-map map.txt

# Symbol/graph/find-legacy analysis verbs
tcl symbols script.tcl --json
tcl diagram script.tcl --json
tcl callgraph script.tcl --json
tcl symbolgraph script.tcl --json
tcl dataflow script.tcl --json
tcl command-info HTTP::uri --dialect f5-irules --json
tcl find-legacy rule.irule --json

# iRules-specific lookups live on the f5 CLI:
f5-query irule event-order rule.irule --json
f5-query irule event-info HTTP_REQUEST --json

# Emit bytecode disassembly
tcl dis script.tcl

# Compile to WASM binary (+ optional WAT sidecar)
tcl compwasm script.tcl -o out.wasm --wat-output out.wat

# Emit ANSI-highlighted output (or --format html)
tcl highlight script.tcl --force-colour

# Diff two iRules using compiler structure layers
tcl diff old.irule new.irule --show ast,ir,cfg

# Use compiler explorer views from the same binary
tcl explore script.tcl --show ir,cfg,opt

# Search KCS help docs (optionally scoped by dialect)
tcl help taint analysis --dialect f5-irules

# Show help for the help command itself
tcl help --help

# Emit help search results as JSON
tcl help taint --json

# Derive version ranges for a package's commands from three local release
# snapshots, and validate the result
tcl spec import --snapshot 1.0=rel/1.0 --snapshot 1.2=rel/1.2 --snapshot 2.0=rel/2.0 \
  --dialect tcl8.6 --out mylib.tclspec

# ...or from a GitHub repository's release tags
tcl spec import --github tcltk/tcllib --tag-pattern 'tcllib-*' --limit 8 \
  --complete-history --out tcllib.tclspec

For iRules input, pass --dialect f5-irules explicitly:

tcl lint rules/ --dialect f5-irules

iRules-specific verbs (event-order, event-info) live on the separate f5 CLI under the irule verb group — see the F5 BIG-IP CLI section.

For source builds, run make kcs-db first so the tcl help command can query the bundled KCS SQLite database.

Install the tcl CLI — the released artefact is the native tcl binary; no Python required. See INSTALL-cli.md for the one-line curl | sh installer, manual install steps for macOS/Debian/Ubuntu/RHEL/CentOS/ Fedora, source builds, and shell completion (bash, zsh, fish) that covers every verb, dialect, optimiser profile, and source-path glob — the same indexed-source extension set the server walks, from the one catalogue, rather than a list of its own.

Differential fuzzer (tcl-fuzz)

tcl-fuzz compares a generated Tcl program between two engines and saves a seeded reproducer whenever their behaviour differs. Build it with cargo build -p tcl-fuzz. A release pin is a property of the whole pair, not just the subject: use a pair whose engines can both honour --tcl-version.

# Both native Rust engines emulate the same selected Tcl release.
tcl-fuzz run --reference runtime-rust --subject tclvm --tcl-version 8.6

# A release-aware finding is found and replayed at its recorded release.
tcl-fuzz replay 12345 --reference runtime-rust --subject tclvm

Pinned findings live below a tclX.Y directory, so the same pair and seed at Tcl 8.6 and Tcl 9.0 cannot overwrite one another. tclsh is a fixed-release binary and cannot accept --tcl-version; select a matching build with --tclsh, and the fuzzer verifies its reported release before starting. See the fuzz-finding triage guide for replay and investigation details.

Packaging & environments

tcl pkg is a deterministic Tcl package manager using Go-style Minimum Version Selection and a content-addressable SHA-256 cache. tcl venv creates isolated virtual environments that pin a specific tclsh version.

# Quick start
tcl venv create .venv            # create a virtual environment
source .venv/bin/activate        # activate it
tcl pkg init                     # create tclpkg.tcl manifest
tcl pkg add json 1.0             # add a dependency
tcl pkg install                  # resolve, fetch, and lock
tcl pkg tree                     # show dependency tree
tcl pkg verify                   # check integrity hashes

The manifest is a native Tcl file (tclpkg.tcl) evaluated in a sandboxed interpreter. The lockfile (tclpkg.lock) is canonical JSON — two runs against the same manifest produce byte-identical output (aside from the generated timestamp, which --frozen preserves).

# tclpkg.tcl — example manifest
package     myapp
version     1.0.0
license     MIT
tcl         >=8.6

require json    1.3.5
require http    2.9.8
dev-require tcltest 2.5.5

The LSP server auto-detects tclpkg.tcl projects and venv lib/ directories, and offers an "Install via tclpkg" quick-fix on missing-package diagnostics.

See docs/kcs/features/kcs-feature-tcl-pkg.md for the full architecture and contracts.

Suppressing diagnostics

Diagnostics can be suppressed at five different scopes. Smaller scope is always better — turning a code off globally hides real problems in future projects.

Inline — put on the line before the command:

# noqa: W100
expr $x + 1

# noqa: *
eval $user_input

Top-of-file — before the first non-comment line:

#!/usr/bin/env tclsh
# tcl-lsp: disable=W100,O111

Project config — .tcl-lsp.ini at the workspace root (commit with source):

[diagnostics]
disabled = W111, IRULE1005

[optimiser]
disabled = O109

For the complete reference, see docs/kcs/kcs-howto-suppress-diagnostics.md.

Excluding files from diagnostics entirely

The scopes above turn individual codes off. To turn all diagnostics off for files matching a glob — for example, .ruff documentation files containing purely virtual procs — use [diagnostics] exclude in .tcl-lsp.ini or the global config.ini, one pattern per line:

[diagnostics]
exclude =
    docs/**
    generated/[a-c]*.tcl
    *.ruff

A pattern with a / matches the file's path relative to its workspace folder root; a pattern with no / matches the file's name at any depth, gitignore-style. A matching file publishes no diagnostics at all — every code, not a subset — while hover, completion, navigation, and formatting keep working on it. The server watches .tcl-lsp.ini, so saving it re-applies the exclusion list with no restart. See docs/kcs/kcs-howto-exclude-files-from-diagnostics.md for the full glob syntax and multi-root behaviour.

Diff and compare views (VS Code)

The analyser never runs on diff content — a diff editor is two real documents rendered side by side, and the modified side of a Git diff from Source Control (or either side of Compare With…) is a real file, analysed like any open file. The squiggles a diff shows are therefore that file's own correct, whole-file diagnostics, and they are shown by default. Because most of those findings predate the change under review, you can optionally hide them while a file is shown only in a diff editor:

"tclLsp.suppressDiagnosticsInDiffEditors": true

The moment the same file is also open in a normal editor — where you might be editing it — its diagnostics come back, so analysis of files you are working on is never affected. This is a VS Code display choice only: the server keeps analysing and no diagnostics are lost. See docs/kcs/kcs-howto-hide-diagnostics-in-diff-views.md.

Changing how prominent a diagnostic is

Some checks are intentionally quiet — an unused variable (W211), a dead store, or a style hint render at hint severity, a faint underline that is easy to miss. Rather than turn a check off, you can re-level it per code so the editor shows it more (or less) prominently:

{ "tclLsp.diagnosticSeverity.W211": "warning" }

Accepted values are "error", "warning", "information", and "hint", plus "default" (keep the analyser's built-in severity). This changes only how the diagnostic is displayed — never whether the analysis runs. Any diagnostic code can be re-levelled with tclLsp.diagnosticSeverity.<CODE>; combine it with the tclLsp.diagnostics.<CODE> on/off toggle above. In .tcl-lsp.ini:

[diagnosticSeverity]
W211 = warning

Multi-file projects and package require

In a project with an "entry" file that runs the package requires and then sources the rest, the individual modules use the required commands without a package require of their own. The missing-package require check (W120) does not flag them:

• Automatically — the server builds a workspace source graph and each module inherits the package requires of every file that (transitively) sources it. Only literal source path.tcl targets are followed.

• Explicitly — when the entry file uses a computed source path (or you prefer to pin it), list the entry files in .tcl-lsp.ini; their combined requires then apply project-wide and the automatic path is turned off:

  [project]
  entryPoints =
      main.tcl
      src/app.tcl
  

Diagnostic and optimiser codes

Every code has its own page — what it means, why the check exists, a triggering example, and the fix:

• Diagnostic codes — the E, W, S, T, and IRULE families
• Optimiser codes — the O family
• Per-code KCS pages — one note per code

iRules-only codes are listed in README-f5.md.

Configuration

Every setting is available in each editor's own settings UI, and in an INI file for editor-independent configuration.

• Which settings exist, and what they do — tclLsp.* reference
• Where the server reads configuration from, and which layer wins — kcs-qa-how-tcl-lsp-loads-configuration.md
• Valid INI sections and keys — kcs-qa-what-config-sections-are-valid.md
• Picking a dialect — kcs-feature-dialect-selection.md
• Formatter options — kcs-feature-formatting.md

In VS Code, Tcl: Export Settings writes your current configuration out as an INI file you can commit alongside the project.

Screenshots

Diagnostics & quick fixes

Hover & completions

Security taint analysis

Semantic highlighting

Building and contributing

• A Rust toolchain (current stable) via rustup. The workspace tracks the floating stable channel; current stable is 1.98.0, released 2026-08-18.
• Node.js 24+ with npm (pinned to v12 via packageManager; run corepack enable npm)
• VS Code 1.93+

git clone https://github.com/bitwisecook/tcl-lsp && cd tcl-lsp
make test                  # the whole suite
make build-editor-vsix     # build the VS Code .vsix

make help lists every target. For the development workflow — the gates to run before pushing, how to add a diagnostic or a formatter option, the repository layout, and the code-style rules — see AGENTS.md and CONTRIBUTING.md.

Acknowledgements

This project was inspired by:

• Picol by Salvatore Sanfilippo (antirez) -- a minimal Tcl interpreter in C that demonstrates the elegance of the Tcl parsing model
• iRuleScan by Simon Kowallik -- a security scanner for F5 iRules
• tclint-vscode by Noah Moroze -- a Tcl linter with VS Code integration

AI

This project used AI very heavily.

• The core parser, lexer, IR, CFG were largely hand created with input on AI about structure, and lots of AI code review.
• The command registry was seeded by hand then filled out with AI.
• The vscode extension, compiler explorer, editor integrations, CI/CD, build pipelines VM, and compiler to Tcl bytecode were all entirely vibe coded.
• The Claude skills, AI integrations were vibe coded with hand work on the prompts .. they need more of that.
• The vast bulk of tests were AI written, AI ported from sources like Tcl, but all largely directed by me in their creation. If I'd been doing that by hand you'd see 3 tests and they'd all be "make install worked for me, good luck"
• Claude Opus 4.6, Gemini 3.1 Pro and OpenAI GPT-5.3-Codex were all used to review the code, critise it, rewrite and reorganise it.

License

This project is licensed under the GNU Affero General Public License v3.0 (AGPL-3.0-or-later).

You are free to use this tool as-is. If you modify the code or incorporate portions of it into another project, the AGPL requires that the complete source of the derivative work is made available under the same license.

Upstream contributions strongly preferred. If you improve or extend this project, please submit your changes back as a pull request rather than maintaining a private fork. See CONTRIBUTING.md for details.