KiCad Custom Design Rules

KiCad Custom Design Rules — VS Code extension

Syntax highlighting, completion, hover help, diagnostics with quick fixes, an outline and a formatter for KiCad Custom Design Rule files (.kicad_dru) in Visual Studio Code — desktop, vscode.dev and github.dev.

A .kicad_dru file with a typo underlined and a "Change to 'clearance'" quick fix

_{Rendered from the extension's own grammar and diagnostics engine.}

KiCad ships a single-line textbox in Board Setup → Custom Rules and a Check Rule Syntax button. That works for one-liners. For real rule sets you want a real editor — multi-cursor, search, and colour that distinguishes condition operators from A.NetClass accessors from layer names from string literals. This extension adds that for .kicad_dru specifically.

Features

Syntax highlighting scoped to .kicad_dru. Keywords (version, rule, constraint, condition, layer, severity, disallow), constraint types (clearance, hole_clearance, track_width, length, assertion, …), token-expression accessors (A.NetClass, B.intersectsArea, …), operators, layer names, severities, comments, strings, and numbers with units are all coloured distinctly.
Snippets for the common rule shapes: starter rule block, clearance by netclass, disallow, length matching, via and track sizing, hole-to-hole, assertion. Type the prefix in a paren context, accept, tab through.
IntelliSense completion. Inside (condition "…") / (constraint assertion "…") strings: a receiver and . (A., B., AB.) gets its properties, an identifier boundary gets receivers and functions; inside A.Type == '…' the item types, and inside A.Layer == '…' / existsOnLayer('…') the layer names. While writing the rule structure: after (constraint you get constraint types, after (layer layer names (both F.SilkS and F.Silkscreen styles), after (severity severities, after (constraint disallow the categories. Each item shows its type/units or argument shape and a short doc.
Hover help. Hover a constraint type, property, function, layer, severity, or disallow category to see what it is, its argument/type, and a one-line description.
Diagnostics with quick fixes. Definite mistakes are underlined as you type — a misspelled constraint type, keyword, layer, property or function ("did you mean clearance?"), a unit on a unitless constraint, a second constraint of the same type in one rule, a missing (version 1). Press Ctrl+. to apply the fix.
Outline and Go to Symbol. Every rule appears in the Outline panel and breadcrumbs with its clauses; Ctrl+Shift+O jumps to a rule by name.
Format Document (Shift+Alt+F). One clause per line under each rule, consistent indentation, comments kept in place. String contents are never touched, and a file with a syntax error is left as-is.
Regions. Wrap related rules in # region Power … # endregion to fold them as a block; the label shows as a section header in the minimap.
Editor niceties: # line comment toggling, paren matching, folding on each multi-line ( … ) block, auto-closing pairs.
Works in the browser: vscode.dev and github.dev, not just desktop.

Completion, hover and diagnostics are backed by a single data/api.json audited against the KiCad 10.0.0 source.

What this extension does not do

It is not a full validator. Diagnostics flag only what KiCad definitely rejects as errors (unbalanced parentheses, a missing (version 1) header, unknown constraint types or keywords, bad severity / disallow / zone_connection values, units on unitless constraints, duplicate constraints or (layer …) clauses in one rule), and likely mistakes as warnings (an A./B. property or function the catalogue doesn't know, a deprecated alias, a misspelled layer name, an A.Type comparison that can never match, a KiCad 11 / master-only token). When unsure it stays silent — renamed layers, for instance, are never flagged. KiCad's own Check Rule Syntax button remains the source of truth for whether a rule is valid. Tune or disable with the kicad-dru.diagnostics setting (all / errors / off).
It does not parse .kicad_pcb, .kicad_sch, .kicad_sym, or any other KiCad file. Those have other extensions (DanielMeza.kicad-syntax- highlighter covers most of them; oaslananka.kicadstudio covers KiCad workflows end-to-end). This extension intentionally stays focused on .kicad_dru so that DRU support is first-class instead of incidental.
It does not check rule semantics (value ranges, whether a constraint makes sense on a layer, cross-rule interactions). That is KiCad's job.

Installation

From the VS Code Marketplace:

ext install cimos.kicad-dru

Or search for "KiCad Custom Design Rules" in the Extensions view. Users of VSCodium, Cursor and other Open VSX-based editors can install it from Open VSX.

A .vsix is also attached to each GitHub release if you prefer manual installation:

code --install-extension vscode-kicad-dru-<version>.vsix

KiCad ≥ 7 supports launching an external editor on a file via Preferences → Configure Paths → External Tools. Pointing it at VS Code gives you a one-click round trip from the KiCad PCB editor to this extension's editor view. Save the file in VS Code, switch back to KiCad, and re-run Check Rule Syntax.

Contributing

Pull requests are welcome — especially for grammar gaps you hit on a real rule file. Please attach a minimal .kicad_dru snippet that demonstrates the issue.

npm ci
npm test                  # grammar snapshots + assertion cases + unit tests
npm run test:integration  # launches a real VS Code with only this extension

All language logic lives in plain, vscode-free modules under src/ (completion, hover, diagnostics, symbols, format, folding), driven by data/api.json; src/extension.ts only adapts them to VS Code. CI runs both suites on every pull request.

Issues: https://github.com/Cimos/vscode-kicad-dru/issues

License

MIT.