Badbox

Deterministic bad-pattern detection for codebases.

Badbox lets a repository encode questionable engineering patterns as structural rules, then check for them without an LLM. It reports evidence—where a pattern occurred, who owns it, and how often— while leaving the decision to a developer or coding agent.

Badbox ships no default policies and performs no automatic rewriting. Each project owns its rules under .badbox/.

Current npm version: 0.3.0

Current rule format: #badbox 1 (experimental)

Contents

• Install
• Quick start
• How Badbox works
• Write rules
• Capabilities
• Supported languages
• CLI
• Programmatic API
• Architecture
• Current boundaries
• Development
• Releasing
• License

Install

Badbox requires Bun 1.3.14 or newer.

Install it in a project:

bun add --dev badbox

Then run it through bunx:

bunx badbox check

You can also install the CLI globally:

bun add --global badbox
badbox check

Published packages include prebuilt native engines for these platforms:

Installing from npm on a supported platform does not require a local Rust toolchain.

Quick start

Run create from the root of the project you want to check:

bunx badbox create project-rules.badbox

Badbox creates .badbox/project-rules.badbox with the correct version header and an editable example. Replace that example with a rule for your project:

#badbox 1

rule rust/excessive-clones for rust {
  summary "Function contains more clone calls than the configured limit"
  param limit = 4

  find code(value) `value.clone()`
  group by nearest callable
  when count > limit

  report {
    severity warning
    message "Function contains excessive clone calls"
    evidence "clone call sites"
  }
}

Check the project:

bunx badbox check

Or check specific source roots while still loading rules from the project's .badbox/ directory:

bunx badbox check src packages

A finding is an observation, so findings do not make the command fail. Invalid rules, invalid input, unreadable files, I/O errors, and syntax diagnostics make the check incomplete and return a nonzero exit code.

How Badbox works

A rule selects syntax, assigns each match to an owner, applies structural conditions, counts the remaining matches, and reports owners above a threshold.

find -> where -> nearest owner -> distinct-range count -> threshold -> finding

This makes rules useful for patterns such as:

• excessive cloning, casting, unwrapping, or goroutine creation per function;
• syntax inside a loop or another structural boundary;
• an owner that contains or lacks supporting evidence;
• one statement following or preceding another in the same lexical block;
• repository-specific architectural patterns that should not reappear.

Badbox detects which supported languages occur under the requested source roots and runs only the relevant rules.

Write rules

The tiny DSL is the primary rule format. Every file starts with a version header:

#badbox 1

Structural captures

Names declared in code(...) become structural captures:

find code(value) `value.clone()`

Undeclared identifiers remain literal source syntax. Captures can also be constrained by text:

where text(method) in ["unwrap", "expect"]

Supported text operators are ==, !=, in, not in, and matches.

Structural relations

Rules can inspect containment and evidence around a selected match:

where match inside any {
  node for_statement
  node while_statement
}

where group lacks any {
  code(ctx) `ctx.cancel()`
}

Ordering relations compare statements in the same nearest callable and lexical block:

find code(statement) `statement.clearBindings()`
group by nearest callable

where match follows any {
  code(statement) `statement.reset()`
}

Repeating statement in both selectors requires the captured source text to be equal. Therefore, first.reset() does not satisfy a later second.clearBindings() match. Intervening sibling statements are allowed; nested callables and different branch, loop, switch, or error-handling blocks remain separate.

See the tiny DSL reference for the complete grammar, validation rules, relations, parameters, and fixture declarations. Runnable DSL examples live under examples/rules. YAML equivalents under examples/yaml exercise the compatibility frontend; they are never loaded automatically.

Capabilities

Supported languages

Badbox bundles 30 parsers.

The 28 ast-grep built-in languages are Bash, C, C++, C#, CSS, Dart, Elixir, Go, Haskell, HCL, HTML, Java, JavaScript/JSX, JSON, Kotlin, Lua, Markdown, Nix, PHP, Python, Ruby, Rust, Scala, Solidity, Swift, TSX, TypeScript, and YAML.

Badbox also statically links PowerShell and Zig parsers.

File extensions select relevant language rules. This is language detection, not framework, dependency, build-configuration, or semantic type detection.

CLI

badbox create <name.badbox>
badbox check [path ...]

create

Creates .badbox/<name.badbox> with the current version header and a Rust example. The name may include subdirectories under .badbox/. Badbox refuses absolute paths, parent traversal, names without the .badbox suffix, and existing files.

check

Recursively loads .badbox, .yaml, and .yml rule files from the current project's .badbox/ directory. With no source paths, it checks the current project. Explicit source paths narrow source discovery but do not change where rules are loaded from.

Discovery respects ignore files and hidden paths, skips common build and vendor directories, and does not follow nested symlinks.

Programmatic API

Use badbox/checker when another tool or coding agent needs structured results:

import { inspect, iterateFindings } from "badbox/checker";

const result = await inspect({
  paths: ["./src"],
  rulePaths: ["./.badbox"],
  parameters: {
    "rust/excessive-clones.limit": 6,
  },
  maxFindings: 1_000,
});

for (const finding of iterateFindings(result)) {
  console.log({
    rule: finding.rule.id,
    file: finding.file,
    owner: [finding.ownerStart, finding.ownerEnd],
    observed: finding.observed,
  });
}

if (result.diagnostics.length > 0) {
  console.error(result.diagnostics);
}

inspect() also accepts:

• threshold to replace every loaded rule's threshold;
• profile: true to include phase timings and cache/execution counters;
• maxFindings to bound returned records while retaining the exact findingCount.

Findings are stored as five u32 values: file ID, rule ID, owner start, owner end, and observed count. File paths and rule metadata are interned separately. Use iterateFindings() to decode the records without materializing another result array.

Architecture

flowchart TD
    CLI["CLI or TypeScript inspect()"]
    Native["Native N-API boundary"]
    Frontend["DSL or YAML frontend"]
    IR["Badbox Rule IR"]
    Plan["Per-language shared finder plan"]
    Parser["Tree-sitter parsing and bounded caches"]
    Match["ast-grep structural backend"]
    Eval["Ownership, relations, counting, thresholds"]
    Result["Compact findings and metadata"]

    CLI --> Native --> Frontend --> IR --> Plan --> Parser --> Match --> Eval --> Result

Parsing, matching, ownership, relational evaluation, counting, thresholds, and compact result construction run in Rust. TypeScript invokes the native engine and decodes metadata.

Badbox owns the Rule IR and structural-backend interface; ast-grep is an implementation detail. Identical primary and relational selectors are interned across a language plan and dispatched once per relevant AST node. Rule-specific predicates, ownership, thresholds, and reporting remain independent.

File work uses at most four native workers. Compiled-rule, parsed-file, and compact-result caches are content-validated, process-local, and bounded. Parallel results are sorted before returning so output remains deterministic.

Current boundaries

• Badbox reports lexical and structural evidence, not runtime behavior or developer intent.
• There is no type resolution, macro expansion, conditional-compilation filtering, SQL query-plan analysis, leak proof, or transaction-atomicity proof.
• Counts describe syntax sites, not runtime execution counts or costs.
• Immediate-sibling ordering is not implemented. follows and precedes allow intervening sibling statements.
• Ordering by nearest callable currently targets Rust, Go, PowerShell, and Zig.
• Only strict greater-than count aggregation is implemented.
• Syntax-error files produce diagnostics and no partial findings.
• Caches do not survive a CLI process and still read file contents for validation.
• Findings are bounded to 10,000 records by default. Increasing maxFindings adds 20 bytes per returned finding.
• Rule format version 1 remains experimental.

Development

Building from source requires Bun, Rust/Cargo, cargo-nextest, and a C compiler for Tree-sitter grammars.

bun install
bun run build:native
bun run ci

bun run ci is the canonical full check. It runs Rust formatting, Clippy, both cargo-nextest suites, the native release build, TypeScript checking, and all Bun tests.

After changing Rust, rebuild the .node addon before running Bun tests:

bun run build:native
bun test tests/scanner.test.ts

For reproducible latency, rule-scaling, and memory measurements:

bun run build:native
bun run benchmark
bun run benchmark ../zova

See the benchmark methodology, optimization report, and frozen Zova corpus.

Project layout

Releasing

All six npm packages and both Rust manifests must use the same release version. Validate that invariant before publishing:

bun run scripts/validate-release.ts 0.3.0
bun run ci

After committing and pushing the version, run the Release npm packages GitHub Actions workflow with that version. It builds and tests all five native targets, packages and smoke-tests the npm tarballs, publishes the platform packages first, and publishes badbox last.

All six npm packages use npm trusted publishing through GitHub OIDC; no NPM_TOKEN is required. Stable versions publish under latest, while prerelease versions publish under next.

License

MIT © 2026 Octacity