napkin

An open-source, drag-and-drop desktop CAD tool for homeowners doing their own furniture, deck, and permit-adjacent building projects — no CAD training required.

It's meant to replace graph paper, a tape measure, and a photocopied code table for the kind of project a homeowner with basic DIY skills reliably does themselves: a coffee table, a deck, moving a window on an exterior wall, a shed-scale addition. Two things make it more than a drawing tool:

• It sizes structural elements against the IRC's homeowner prescriptive-code shortcuts (header spans, wall bracing, deck framing) so a straightforward project can be sized correctly without hiring a structural engineer — and it always cites the code edition, table, and row behind every number, rather than asserting a bare answer.
• It generates cut lists and materials lists from the same drawing, resolving nominal lumber and sheet-goods sizes (a "2x4" is really 1.5"×3.5") to their true dimensions.

napkin is not a substitute for a permit office, an inspector, or a licensed engineer. It's scoped deliberately to the prescriptive-code band of projects — the moment a project's inputs fall outside what a published table covers, the tool says so and stops, rather than guessing.

See DESIGN.md for the full design and implementation document: vision, scope, architecture, and the decisions made so far. Detailed designs live under docs/design/, starting with the geometry model (lengths, entities, relationships, the update interface).

Status

Beta. M1 through M9 are done: open and draw a sample design with dimensions (M1); draw, resize by typing a dimension, undo, save (M2); the coffee table's cut list and shopping list (M3); a header size with the code row it came from (M4); the bracing check and switching adopted codes (M5); the standard views and the Parts view (M6); sketch mode (M7); renovation — existing, new and demolished work (M8); angled parts, grain and a cost estimate (M9, v0.170.0-beta). Open: M10 Real code (waiting on where the IRC tables are read from, #209), M11 Deck and three-season porch (design awaiting sign-off), M12 Print and cut and M13 Permit set.

The work is organised into milestones, each of them something you can hold rather than a layer of the architecture — M1 Look, M2 Draw, M3 Cut, M4 Check, M5 Brace and compare, Hardening, M6 Views and drawings, M7 Sketch mode, M8 Renovation, M9 Shape, M10 Real code, M11 Deck and three-season porch, M12 Print and cut and M13 Permit set. What each one gets you, and which issues build it, is the milestone table in PLAN.md; the same milestones are on the issue tracker.

napkin is a beta indefinitely: every release is a pre-release, breaking changes are always allowed, and there is no migration path between betas (an older project file gets a clear "unsupported version" error, not a conversion). See DESIGN.md §12.

Trying it

Unsigned pre-releases are on the Releases page: zips for macOS (Apple silicon and Intel) and Windows x64, with SHA256SUMS.txt. Or run it from source (see Building).

Building

Requires the .NET 10 SDK (LTS, supported through November 2028) — pinned in global.json.

dotnet build
dotnet test
dotnet run --project src/Napkin.App

Project layout

src/
  Napkin.Core.Geometry        # platform-agnostic geometry: points, lines, dimensions, units
  Napkin.Core.Materials       # the materials library: stock lumber, panels, hardware, fasteners
  Napkin.Core.RulesEngine     # prescriptive tables keyed by adopted code + evaluation
  Napkin.Core.Project         # project file format: scene graph, serialization
  Napkin.Modules.Furniture    # parts, joinery, cut lists, materials lists
  Napkin.Modules.Building     # sites, walls, openings, decks — consumes the rules engine
  Napkin.Modules.Editing      # the editing model: design editor, undo, snapping, drawing tools
  Napkin.Interop.Dxf          # the plan as DXF 2000 (ACadSharp)
  Napkin.Interop.Pdf          # true-scale PDF sheets with title blocks (Excise.Core, vendor/excise)
  Napkin.App                  # Avalonia UI (Windows + macOS)
tests/
  Napkin.Core.RulesEngine.Tests   # golden tests against each state's published adopted text
  Napkin.Core.Geometry.Tests
  ...                              # one test project per src/ assembly, plus Napkin.App.GuiTests

DXF export (Napkin.Interop.Dxf, #23) and PDF sheets (Napkin.Interop.Pdf, #25) are in the tree; SketchUp import was closed (#24).

Core.* and Modules.* have no UI dependency — the rules engine in particular is meant to be testable and auditable independent of the app around it.

Versioning

napkin is a pre-1.0 beta indefinitely. Every version is 0.N.0-beta: the minor number goes up by exactly one with each change landed on main (development is direct to main, no pull requests, since 2026-09-22), and nothing is promised to stay compatible between betas. The version is set in one place, Directory.Build.props; see DESIGN.md §12.

License

GNU Affero General Public License v3.0 for this project's own code. Dependencies are kept to permissive (MIT/Apache-2.0/BSD) or weak-copyleft (LGPL/MPL) licenses only — see DESIGN.md §2.1 for the reasoning.

Scope note

Four adopted codes are wanted (DESIGN.md §11), and they arrive one at a time. The 2022 Connecticut State Building Code (IRC 2021 as amended) shipped first, in M4 and M5 — the engine, pack format, overlay, interpolation and picker are complete, and switching a project's adopted code recomputes every result, which is what makes code locking demonstrable. The IRC 2021 base tables themselves are bring-your-own until M10 transcribes them from a primary source (#158/#14). The 2026 Connecticut code (IRC 2024 base) is not yet in force and is not yet encoded. Massachusetts 780 CMR 10th edition and the Pennsylvania Uniform Construction Code come after that. The rules engine is data-driven and keyed by adopted code, not by IRC year, specifically so further jurisdictions are a data change rather than a code change — see DESIGN.md for details. Imperial units only; 2D only.

This is not legal or engineering advice, and it is not a substitute for your local building department's review or a licensed professional's judgment about site-specific conditions a prescriptive table doesn't cover.