ltspice-mcp 0.1.0

MCP server for LTSpice circuit simulation

ltspice-mcp

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

MCP server that exposes LTspice circuit simulation to LLMs via the Model Context Protocol. Create netlists, edit schematics, run simulations, and analyze results through MCP tool calls.

Built on the low-level mcp.server.lowlevel.Server API with spicelib for simulator interfacing and result parsing.

Requirements

• Python 3.13+
• uv package manager
• LTspice (for simulation — circuit editing works without it)

Platform support

Platform	How LTspice runs
Windows	Native
WSL2	Windows LTspice.exe via interop (not Wine)
Linux	Via Wine (spicelib handles this)

Setup

git clone https://github.com/Cognitohazard/ltspice-mcp.git
cd ltspice-mcp
uv sync

cp ltspice-mcp.example.toml ltspice-mcp.toml
# Set simulator.path if LTspice isn't auto-detected (required on WSL)

Add to Claude Code

claude mcp add -s project ltspice -- uv run --directory /path/to/ltspice-mcp ltspice-mcp

Or add to .mcp.json manually:

{
  "mcpServers": {
    "ltspice": {
      "type": "stdio",
      "command": "uv",
      "args": ["run", "--directory", "/path/to/ltspice-mcp", "ltspice-mcp"]
    }
  }
}

WSL configuration

Set the Windows-side LTspice path in ltspice-mcp.toml:

[simulator]
path = "/mnt/c/Program Files/ADI/LTspice/LTspice.exe"

Simulation output is automatically redirected to a Windows temp directory. LTspice writes SQLite .db files alongside results, and these fail on UNC paths (\\wsl.localhost\...), which causes .MEAS data to be lost.

Tool Profiles

tool_profile controls which tools the server exposes. Set via [tools] profile in TOML or LTSPICE_MCP_TOOL_PROFILE env var.

Profile	Tools	Use case
full (default)	All 31	Backwards-compatible default for any MCP client
agentic	16	Recommended when your client supports skill files

The agentic profile removes netlist-editing wrappers, sweep/MC configuration tools, niche schematic operations, and library session management — things a capable LLM agent does better through direct file editing. It keeps simulation lifecycle, binary .raw parsing, batch orchestration, AscEditor-dependent ops, and library search — the tools that provide genuine leverage over what an LLM can do natively.

[tools]
profile = "agentic"

Skills

The tools give LLMs access to simulation. The skills give them the expertise to use it well.

The skills/ directory contains structured domain knowledge that teaches LLMs how to work with SPICE circuit simulators. Each skill is a self-contained reference covering SPICE fundamentals, simulator-specific gotchas, and MCP tool workflows — the kind of knowledge that takes years to build and that LLMs don't reliably have.

Skill	Description
skills/ltspice/SKILL.md	LTspice: .asc schematic editing, Windows/WSL paths, LTspice-specific directives
skills/ngspice/SKILL.md	ngspice: open-source workflow, control scripts, ngspice model compatibility

Copy the relevant skill into whatever location your MCP client uses for persistent instructions, then set the agentic profile. The skill provides the domain knowledge that replaces the removed wrapper tools.

Tools

All 31 tools are prefixed with ltspice_ to avoid namespace conflicts with other MCP servers. Every tool declares MCP annotations (readOnlyHint, destructiveHint, idempotentHint, openWorldHint) for client auto-approval decisions.

Circuit editing (12 tools)

Work on both .cir/.net netlists and .asc schematics. Extension-based dispatch picks the right editor automatically.

Tool	Description
ltspice_create_netlist	Create a new netlist from a content string
ltspice_read_circuit	Read and parse a circuit file (netlist text for .cir, schematic layout for .asc)
ltspice_list_components	List components (optionally filtered by prefix) or look up a single component by reference
ltspice_set_component_value	Set one component value, or batch-set many via a values dict
ltspice_parameter	Get all .PARAM values (no args) or set one (name + value)
ltspice_edit_directive	Add or remove SPICE directives (.tran, .ac, .lib, etc.)
ltspice_remove_component	Remove a component from an .asc schematic
ltspice_move_component	Move or rotate a component in an .asc schematic
ltspice_set_component_attribute	Set a component attribute (SpiceLine, Value2, etc.)
ltspice_add_component	Add a new component to an .asc schematic at a specified grid position
ltspice_add_wire	Add wire segment(s) to an .asc schematic to connect components
ltspice_export_netlist	Export an .asc schematic to a .net netlist

.asc schematic editing requires .asy symbol files. These are auto-detected on Windows and WSL; override with [schematic] symbol_paths in TOML or the LTSPICE_MCP_SYMBOL_PATHS env var.

Simulation (3 tools)

Tool	Description
ltspice_run_simulation	Run a simulation — sync for short runs, async (returns job ID) for long ones
ltspice_check_job	Check a job's status by ID, or list all jobs
ltspice_cancel_job	Cancel a running simulation

Analysis (5 tools)

Tool	Description
ltspice_get_signal_stats	Signal statistics: min, max, mean, RMS, peak-to-peak (dB/phase for AC)
ltspice_query_value	Query a signal's value at a specific time or frequency
ltspice_get_measurements	Extract .MEAS directive results from the simulation log
ltspice_get_operating_point	DC operating point: all node voltages and branch currents
ltspice_get_simulation_summary	Full summary: simulation type, signals, measurements, warnings

Parametric analysis (5 tools)

Tool	Description
ltspice_configure_sweep	Configure a multi-parameter sweep (linear or log, by step size or point count)
ltspice_run_sweep	Execute a configured sweep (async, returns job ID)
ltspice_configure_montecarlo	Configure Monte Carlo analysis with per-type component tolerances
ltspice_run_montecarlo	Execute a configured Monte Carlo analysis (async, returns job ID)
ltspice_get_batch_results	Query sweep/MC job progress, per-signal statistics, or per-run data

Library management (5 tools)

Tool	Description
ltspice_search_library	Search loaded libraries for models/subcircuits by name
ltspice_get_model_info	Get model parameters and the .include directive to use it
ltspice_load_library	Load a .lib/.mod file or a directory of library files
ltspice_unload_library	Unload a previously loaded library
ltspice_list_libraries	List loaded libraries, optionally with their model names

Status (1 tool)

Tool	Description
ltspice_get_server_status	Server status: detected simulators, config, sandbox paths, runtime state

Resources

Static resources and URI templates for browsing circuit files and simulation results.

URI	Description
ltspice://netlists/	List netlist files in the working directory
ltspice://netlists/{filename}	Read the full text of a specific netlist
ltspice://results/	List all simulation and batch jobs with their status
ltspice://results/{job_id}/signals	Signal/trace names from a completed job's .raw file
ltspice://results/{job_id}/measurements	.MEAS results from a completed job's log
ltspice://models/	List loaded model libraries and their models
ltspice://config	Current server configuration and detected simulators

Configuration

Copy ltspice-mcp.example.toml to ltspice-mcp.toml and edit. All settings can be overridden with LTSPICE_MCP_ prefixed environment variables (highest precedence). The config file path itself can be set with --config PATH or the LTSPICE_MCP_CONFIG env var.

[simulator]
default = "ltspice"            # ltspice, ngspice, qspice, xyce (null = auto-detect)
path = ""                      # Explicit executable path (required on WSL)

[security]
allowed_paths = ["."]          # Sandbox: only these directories are accessible

[simulation]
max_parallel = 4               # Concurrent simulation limit
timeout = 300.0                # Default timeout in seconds

[analysis]
max_points = 10000             # Max waveform data points per trace

[plotting]
dpi = 150                      # Plot resolution
style = "seaborn-v0_8-darkgrid"  # Matplotlib style

[schematic]
symbol_paths = []              # Custom .asy symbol paths (auto-detected on Windows/WSL)

[logging]
level = "INFO"                 # DEBUG, INFO, WARNING, ERROR, CRITICAL

Architecture

MCP Protocol    server.py         — lifespan, dispatch, request routing
                resources.py      — MCP resources and URI templates

Tools           tools/circuit.py     — netlist and schematic editing
                tools/simulation.py  — simulation execution and job management
                tools/analysis.py    — waveform analysis and measurements
                tools/advanced.py    — parametric sweep and Monte Carlo
                tools/library.py     — component library management
                tools/status.py      — server diagnostics

Core            lib/sim_runner.py        — spicelib SimRunner async integration
                lib/sweep_runner.py      — parametric sweep execution
                lib/montecarlo_runner.py — Monte Carlo execution
                lib/runner_manager.py    — centralized runner lifecycle and caching
                lib/raw_parser.py        — .raw file parsing and statistics
                lib/log_parser.py        — .log parsing (errors, measurements, Fourier)
                lib/batch_results.py     — sweep/MC batch result extraction
                lib/ltspice_wsl.py       — WSL-aware LTspice subclass
                lib/wsl.py               — WSL detection and path conversion
                lib/simulator.py         — simulator detection and selection
                lib/library_manager.py   — SPICE model library management
                lib/library_parser.py    — .lib/.mod file parsing
                lib/cache.py             — FileCache for editor and result instances
                lib/pathutil.py          — path security (safe_path, resolve_safe_path)
                lib/format.py            — output formatting helpers
                lib/plotting.py          — matplotlib plot generation
                lib/sweep_utils.py       — sweep parameter utilities

Config          config.py  — TOML + env var configuration
                state.py   — session state (jobs, editors, caches)
                errors.py  — structured error hierarchy

Design notes

• Async wrapping: All spicelib operations are synchronous. They run in asyncio.to_thread() via run_sync() to avoid blocking the event loop.
• Path sandbox: User-provided paths are validated against config.allowed_paths. Paths outside the sandbox raise PathSecurityError.
• Runner lifecycle: RunnerManager owns all runner instances (sim, sweep, MC). It auto-invalidates cached runners when the event loop, simulator class, or output folder changes. Runners are never created directly.
• stdin protection: main.py redirects fd 0 to /dev/null before starting the server, passing the real stdin only to the MCP transport. This prevents subprocesses from consuming MCP protocol bytes — a workaround for python-sdk#671.
• Tool annotations: Every tool declares readOnlyHint, destructiveHint, idempotentHint, and openWorldHint for client auto-approval decisions.
• Structured errors: Typed error hierarchy (PathSecurityError, NetlistError, SimulationError variants) in errors.py. Handlers catch LTSpiceMCPError subtypes and return error text; unknown exceptions propagate to the MCP SDK.

Development

uv sync                        # Install dependencies
uv run pytest tests/ -v        # Run tests
uv run pyright                 # Type checking
uv run ltspice-mcp             # Run server (stdio)
uv run ltspice-mcp --config /path/to/config.toml  # Custom config

License

GPL-3.0