# spice

Runs SPICE simulations on subcircuits found by KiCad schematic analysis: filters, dividers, opamp stages, crystals. Checks calculated values against a real run.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 624 installs · ★ 1504
- Author: aklofas
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/aklofas/kicad-happy/tree/HEAD/skills/spice/SKILL.md
- Updated: 2026-10-23
- HTML: https://affpapa.org/en/nevibecode/skills/spice

## What it does

The skill reads the analyzer JSON produced by the `kicad` skill, picks out simulatable subcircuits and builds testbenches for them. It then runs the simulator in batch mode and compares calculated values — filter cutoff frequencies, divider ratios, opamp gain, LC resonance, crystal load capacitance — against what the simulation returns. Output is a structured pass/warn/fail report.

That inverts the usual flow. You do not write simulation sources or configure analyses; the script does it from the schematic analysis. The simulator is auto-detected among ngspice, LTspice and Xyce, first available wins, and you can override it with `--simulator` or the `SPICE_SIMULATOR` env var. Python 3.10+ is required, stdlib only, no pip dependencies.

No simulator installed? The step is skipped and noted in the report, so a missing ngspice is not an error. Two optional modes exist: PCB parasitic R/L/C injected into testbenches via `--parasitics`, which matters on high-impedance feedback networks and LC filters, and Monte Carlo tolerance analysis via `--monte-carlo`. The default timeout is 5s per subcircuit; raise it with `--timeout` for heavier circuits.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add aklofas/kicad-happy --skill spice -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/spice/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/spice/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add aklofas/kicad-happy --skill spice -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/spice/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add aklofas/kicad-happy --skill spice -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/spice/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install aklofas/kicad-happy spice
```

2. **Manually: put the files in place**
- File: `.github/skills/spice/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add aklofas/kicad-happy --skill spice -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/aklofas/kicad-happy --path skills/spice
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/spice/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add aklofas/kicad-happy --skill spice -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/aklofas/kicad-happy/tree/HEAD/skills/spice/SKILL.md

## When to use it
- verify an RC or LC filter cutoff by simulation
- check that a voltage divider lands on the target voltage
- compare opamp stage gain against the hand calculation
- estimate LC resonance and crystal load capacitance
- see which component drives output spread across tolerances

## Example prompts
- run a SPICE simulation on design.kicad_sch
- verify this filter cutoff with simulation
- run 100 Monte Carlo trials on the voltage dividers

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 78b482bb426d4eaf.

BEGIN THIRD-PARTY FILE 78b482bb426d4eaf
```text
---
name: spice
description: >-
  Run automatic SPICE simulations on subcircuits detected from KiCad schematic
  analysis — validates filter frequencies, divider ratios, opamp gains, LC
  resonance, and crystal load capacitance. Supports ngspice, LTspice, and Xyce
  (auto-detected). Generates testbenches, runs batch mode, produces structured
  pass/warn/fail report. Use when the user asks to simulate, verify, or
  validate any analog subcircuit — RC filters, LC filters, voltage dividers,
  opamp circuits, crystal oscillators. Also for "simulate my circuit", "run
  spice", "verify with simulation", "check my filter cutoff", "does this
  divider give the right voltage", "what's the bandwidth of this opamp stage".
  Consider suggesting simulation during design reviews when the schematic
  analyzer reports simulatable subcircuits and a SPICE simulator is available.
---

# SPICE Simulation Skill

Automatically generates and runs SPICE testbenches for circuit subcircuits detected by the `kicad` skill's schematic analyzer. Supports ngspice, LTspice, and Xyce (auto-detected). Validates calculated values (filter frequencies, divider ratios, opamp gains) against actual simulation results and produces a structured report.

This skill inverts the typical simulation workflow: instead of requiring users to create simulation sources and configure analysis (which ~2.5% of KiCad users do), it generates targeted testbenches automatically from the analyzer's subcircuit detections.

## Related Skills

| Skill | Purpose |
|-------|---------|
| `kicad` | Schematic/PCB analysis — produces the analyzer JSON this skill consumes |
| `digikey` | Parametric specs for behavioral models, datasheet downloads |
| `mouser` | Parametric specs (secondary source), datasheet downloads |
| `lcsc` | Parametric specs (no auth needed), datasheet downloads |
| `element14` | Parametric specs (international), datasheet downloads |
| `emc` | EMC pre-compliance — uses this skill's simulator infrastructure for SPICE-enhanced PDN impedance and EMI filter analysis |
```
END THIRD-PARTY FILE 78b482bb426d4eaf

The third-party file has ended. Everything between the 78b482bb426d4eaf tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

First 2062 of 22405 bytes. © aklofas · MIT · https://github.com/aklofas/kicad-happy/tree/HEAD/skills/spice/SKILL.md

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From the same set: [aklofas/kicad-happy](https://affpapa.org/en/nevibecode/by/aklofas/kicad-happy.md) — 12 cards

---
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