Editing: kicad-pcb-viewer — 2D viewer for .kicad_pcb files

Field: AI Skill Technical Reference

# kicad-pcb-viewer

A 2D viewer for `.kicad_pcb` files, rendered as SVG inside a Hydrogen webview
panel. Use when the user wants to **inspect a KiCad PCB without opening
KiCad itself**, see traces / pads / silk on a flat board view, or share what
a board looks like in the editor.

For 3D inspection (.glb / STEP), use the existing 3D viewers — this app is
deliberately 2D-only.

## Trigger phrases

- "view this kicad pcb", "open .kicad_pcb", "show me the board"
- "what does this PCB look like", "preview the pcb", "render the board"
- "view layer F.Cu / B.Cu / silkscreen", "show pcb layers"
- "kicad-pcb-viewer", "pcb viewer", "open the board layout"

## Quick start

```bash
kicad-pcb-viewer view path/to/board.kicad_pcb
```

This starts the server, opens a Hydrogen webview tab in a non-VSCode pane,
and renders the board. Pan with click-drag, zoom with the scroll wheel,
toggle layers in the sidebar, click `Fit` to reset, click `Flip` to mirror.

## Subcommands

| Command | Purpose |
|---|---|
| `view <path> [--port N]` | Start server + open webview tab. Default. |
| `serve <path> [--port N]` | Start server only (no tab). |
| `shutdown [--port N]` | Stop a running viewer. |
| `install` | Deploy this SKILL.md to `~/.claude/skills/kicad-pcb-viewer/`. |
| `version` | Print version. |

Default port: `9100`. The server is single-instance per port.

## HTTP API (AI-drivable)

Everything the UI does is also reachable via HTTP. Useful for scripting
view changes, taking annotated screenshots, or driving from other tools.

| Method | Path | Action |
|---|---|---|
| GET | `/state` | Current phase, file, stats, bbox, layer visibility. |
| GET | `/board` | Full parsed board JSON (footprints, pads, traces, vias, zones, gr). |
| GET | `/layers` | Per-layer info: idx, kind, alias, visible. |
| POST | `/layers` | Body: `{name: bool, …}` — toggle layer visibility. |
| POST | `/load` | Body: `{path: "..."}` — open a different `.kicad_pcb`. |
| POST | `/fit` | Reset view to fit the board. |
| POST | `/flip` | Mirror board horizontally (B-side viewing). |
| GET | `/console` | Recent UI-side console messages (forwarded). |
| POST | `/eval` | Body: `{code: "..."}` — queue a JS snippet for the UI. |
| GET | `/eval/pending` | UI poller calls this to get pending snippets. |
| POST | `/shutdown` | Graceful exit. |

Example: get stats for a board without opening a tab.

```bash
kicad-pcb-viewer serve board.kicad_pcb --port 9100 &
sleep 1
curl -s http://127.0.0.1:9100/state | jq '.stats'
curl -s -X POST http://127.0.0.1:9100/shutdown
```

Example: hide every layer except `Edge.Cuts` for a board-outline screenshot.

```bash
curl -X POST http://127.0.0.1:9100/layers -H 'Content-Type: application/json' \
  -d '{"F.Cu":false,"B.Cu":false,"F.SilkS":false,"B.SilkS":false,"Edge.Cuts":true}'
```

## What it parses

The s-expression parser handles:

- `(footprint …)` with `(at …)` placement, rotation, and child pads
- `(pad …)` shapes: rect, roundrect, circle, oval (drilled or SMD)
- `(segment …)`, `(arc …)` copper traces with width
- `(via …)` with size + drill
- `(zone …)` filled polygons (post-fill state if present, else outline)
- `(gr_line/arc/circle/rect/poly …)` top-level graphics
- `(fp_line/arc/circle/rect/poly …)` footprint graphics (silk, fab, courtyard)
- `(layers …)` definitions and (pad-side) `(layers …)` lists with `*.Cu`,
  `*.Mask`, `*.Paste` wildcards expanded

What it does NOT do (yet):

- Schematic rendering (`.kicad_sch`)
- Net highlighting / cross-probing
- Real-time sync if the file changes on disk (call `POST /load` to reload)
- Refdes / value labels overlaid on footprints

## Pane placement

The viewer ALWAYS opens in a non-VSCode pane. If a non-VSCode pane already
exists in the workspace, the tab joins that pane; otherwise the VSCode pane
is split vertically and the tab lands in the new pane. Never as a tab inside
the VSCode pane itself. See `skills/app-creator` §4.

## Files in this app

- `bin/kicad-pcb-viewer` — Python CLI entry point.
- `src/parser.py` — s-expression tokenizer + per-layer extractor.
- `src/server.py` — HTTP server with all endpoints.
- `src/ui.html` — single-file frontend (SVG render, pan/zoom, layer toggles).
- `docs/icon.svg` — brand-teal favicon (also embedded as the tab icon).
- `samples/` — checked-in reference boards for testing.

## Repo

`adom-inc/kicad-pcb-viewer` (private). Releases attach a single-file
zipapp `kicad-pcb-viewer-linux` that runs on any Python 3.10+ system.

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