Add README with usage docs and examples

Covers motivation, architecture overview, full query reference,
and side-by-side human/JSON output examples.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -0,0 +1,192 @@
+# claude-kicad-helper
+
+A command-line query tool for KiCad project files, designed to extract
+focused, readable information from files that are otherwise too large to
+work with directly.
+
+## Why this exists
+
+KiCad stores schematics (`.kicad_sch`) and PCB layouts (`.kicad_pcb`) as
+S-expression trees that easily run to thousands of lines. Most of that bulk
+is graphical metadata — line coordinates, font sizes, courtyard polygons —
+that is irrelevant when you want to answer questions like:
+
+- What components are on this board and what are their values?
+- Which nets exist in this schematic?
+- What copper traces physically connect to pin 1 of R5?
+
+`kicad-query.mjs` parses the file, extracts structured data, and prints
+only what was asked for — either as a human-readable table or as JSON for
+programmatic/LLM consumption.
+
+## Architecture
+
+```
+tokenize(text)          generic S-expression tokenizer
+parse_sexp(text)        builds { tag, items[] } tree
+        │
+        ▼
+run_query(ext, query, root, args)   file-type + query dispatch → plain data object
+        │
+        ├── render_human(ext, query, data)   formatted tables for terminal
+        └── render_json(data)                JSON.stringify for LLM / scripts
+```
+
+Query functions are pure data transformers — no I/O, no format awareness.
+Adding a new output format only requires a new renderer.
+
+## Requirements
+
+Node.js 18+ (uses ES modules, no dependencies).
+
+## Usage
+
+```
+node kicad-query.mjs [--format=json] <file> <query> [args...]
+```
+
+## Queries
+
+### Schematic (`.kicad_sch`)
+
+| Query | Description |
+|-------|-------------|
+| `summary` | Component counts, wire count, libraries used |
+| `components` | Table of all placed components (ref, value, footprint) |
+| `components ref=U*` | Filter by reference glob |
+| `components value=100nF` | Filter by value glob |
+| `component U1` | All properties and pins of one component |
+| `nets` | All net names (local labels, global labels, power nets) |
+
+### PCB (`.kicad_pcb`)
+
+| Query | Description |
+|-------|-------------|
+| `summary` | Net, footprint, segment, via, zone counts |
+| `nets` | All nets with their numeric IDs |
+| `net GND` | Which pads are connected to a named net |
+| `footprints` | Table of all footprints |
+| `footprint R5` | Position, layer, value, pad→net table for one footprint |
+| `traces R5 1` | BFS through segments and vias from pad 1 of R5 |
+
+### Project (`.kicad_pro`)
+
+| Query | Description |
+|-------|-------------|
+| `summary` | Filename, version, min clearance, section list |
+
+### Generic (any file)
+
+| Query | Description |
+|-------|-------------|
+| `tags` | All S-expression tag names sorted by frequency — useful for exploration |
+| `raw <tag>` | Dump all nodes with a given tag name |
+
+---
+
+## Examples — human output
+
+```
+$ node kicad-query.mjs sketch.kicad_sch summary
+=== Schematic Summary ===
+Components   : 26
+Power symbols: 14
+Net labels   : 0
+Global labels: 16
+Wires        : 102
+
+Libraries:
+  Amplifier_Operational: 1
+  Connector: 4
+  Device: 16
+  Mechanical: 4
+```
+
+```
+$ node kicad-query.mjs sketch.kicad_sch components
+Reference  Value             Library:Symbol               Footprint
+---------  -----             --------------               ---------
+C1         100 nF            Device:C                     Capacitor_SMD:C_0603_1608Metric
+C5         100 µF            Device:C_Polarized           Capacitor_SMD:CP_Elec_6.3x4.5
+R4         100 mΩ            Device:R                     Resistor_SMD:R_1206_3216Metric
+U1         LM358             Amplifier_Operational:LM358  Package_SO:SO-8_3.9x4.9mm_P1.27mm
+...
+```
+
+```
+$ node kicad-query.mjs sketch.kicad_sch nets
+=== Net Names (10 total) ===
+  BIAS  [global]
+  Current Measurement  [global]
+  GND  [power]
+  SUPPLY  [global]
+  VDD  [power]
+  Voltage Reference  [global]
+  ...
+```
+
+```
+$ node kicad-query.mjs sketch.kicad_pcb traces R5 1
+=== Traces from R5 pad 1 ===
+Net        : Current Reference (id=12)
+Position   : (148.645, 64.350)
+Pad layers : F.Cu
+
+Layer B.Cu — 2 segment(s):
+  From (x, y)           To (x, y)             Width
+  (153.162,  74.168)  → (153.670,  73.660)    0.4mm
+  (153.162,  81.026)  → (153.162,  74.168)    0.4mm
+
+Layer F.Cu — 9 segment(s):
+  ...
+
+Vias (2):
+  (153.670, 73.660)  F.Cu ↔ B.Cu
+  (153.162, 81.026)  F.Cu ↔ B.Cu
+```
+
+---
+
+## Examples — JSON / LLM output
+
+Add `--format=json` before the filename. All queries produce the same data;
+only the presentation changes.
+
+```
+$ node kicad-query.mjs --format=json sketch.kicad_sch components
+{
+  "components": [
+    {
+      "ref": "C1",
+      "value": "100 nF",
+      "footprint": "Capacitor_SMD:C_0603_1608Metric",
+      "lib_id": "Device:C",
+      "datasheet": "~",
+      "dnp": false
+    },
+    ...
+  ]
+}
+```
+
+```
+$ node kicad-query.mjs --format=json sketch.kicad_pcb traces R5 1
+{
+  "ref": "R5",
+  "pad": "1",
+  "net": { "id": 12, "name": "Current Reference" },
+  "position": { "x": 148.645, "y": 64.35 },
+  "pad_layers": ["F.Cu"],
+  "traces": [
+    { "layer": "F.Cu", "start": { "x": 149.225, "y": 64.35 }, "end": { "x": 148.645, "y": 64.35 }, "width": 0.4 },
+    ...
+  ],
+  "vias": [
+    { "position": { "x": 153.670, "y": 73.660 }, "layers": ["F.Cu", "B.Cu"] }
+  ]
+}
+```
+
+When feeding KiCad data to an LLM, prefer `--format=json` with targeted
+queries over pasting raw file contents. A 6000-line schematic collapses to
+a few hundred bytes of component and net data.