ltspice-mcp

ltspice-mcp

Work in progress. Core functionality is usable but expect rough edges and breaking changes.

An MCP server that connects LLM assistants (Claude, and any other MCP client) to real circuit simulation: LTspice and ngspice, plus direct editing of LTspice .asc schematics. Simulation results come back as structured numbers — cutoff frequencies, overshoot, phase margin, rise times, and per-device small-signal internals (gm, gds, vth, …) read back by name — so the assistant can design, verify, and iterate on circuits in the same files you open in LTspice, without ever hand-parsing a rawfile. Built on spicelib.

Quick start

1. Install the server:

uv tool install ltspice-mcp     # or: pip install ltspice-mcp / pipx install ltspice-mcp

2. Add it to your MCP client:

# Claude Code
claude mcp add -s project ltspice -- ltspice-mcp

// Claude Desktop (claude_desktop_config.json) and most other clients
{
  "mcpServers": {
    "ltspice": { "command": "ltspice-mcp", "args": [] }
  }
}

3. Have LTspice or ngspice installed. Both are auto-detected on Windows, Linux, and macOS; on WSL the LTspice path must be set explicitly (WSL notes). Circuit editing works with no simulator at all.

That's the setup. Python 3.11+ required. Verify with ltspice-mcp --help.

Claude Desktop config lives at ~/Library/Application Support/Claude/ (macOS), %APPDATA%\Claude\ (Windows), or ~/.config/Claude/ (Linux). Cursor, Windsurf, Gemini CLI, Continue, Cline, Zed and others take the same JSON snippet in their respective config files. Web clients (claude.ai, ChatGPT) need a stdio→HTTP bridge such as mcp-proxy — only expose this server on a network you fully control, since it writes files and spawns processes inside allowed_paths.

Install as a Claude Code plugin or Desktop Extension

Two lower-friction routes that wrap the same PyPI package:

• Claude Code plugin — /plugin marketplace add cognitohazard/ltspice-mcp, then /plugin install ltspice-mcp. Registers the server (via uvx) and bundles the LTspice/ngspice skills. To test against a local checkout instead, /plugin marketplace add ..
• Claude Desktop extension — build the .mcpb in packaging/mcpb/ and drag it onto Claude Desktop for a one-click install with a native folder picker for your circuits directory.

Both wrap the server; they still need uv and a simulator on the host — they do not bundle LTspice or ngspice.

Using it

Once connected, you ask for circuit work in plain language. The assistant designs the circuit and decides what to measure; the server runs the simulator, parses the binary output, and hands back the numbers. It reports what the run produced, the simulator's own warnings included, and leaves the call on whether a result is good to you and the assistant.

"Bias this NMOS common-source stage into saturation at the target drain current and report gm/ID."

The assistant writes the netlist — with a .save for M1's operating-point internals — runs a .op on ngspice, and reads the bias point back by name: VDS against the device's own VDSAT so you can see it's saturated, the drain current, and gm and gds straight from the solver. gm/ID, the figure analog designers size to, follows from gm and ID. If the bias is off, it trims the gate reference or W/L and re-runs, a couple of seconds per pass. (On LTspice the same .op returns node voltages and branch currents; per-device internals are an ngspice feature, and they have to be .saved to appear.)

Other requests that work the same way: