mcp-spice

mcp-spice runs bounded ngspice analyses behind MCP and keeps every result tied to the exact circuit bytes that produced it.

JSR · container · technical documentation · changelog · security

A read-only MCP App projecting an exact recorded operating-point artifact from a Digital Thread project. The values, units, source symbols, artifact identity, and projection fingerprint all come from the recorded result.

What it provides

• Content-addressed admission for exact UTF-8 circuit netlists.
• Bounded operating-point, transient, and DC-sweep analyses through ngspice.
• Compact structured results instead of unbounded raw curves.
• Immutable documentary receipts and exact result readback across restarts.
• Small MCP Apps for a result or receipt, built from shared MCP View components.

The server reports numerical observations and declared analysis limits. It does not decide whether a circuit satisfies a requirement, and a successful execution is not a proof or compliance verdict.

Run it

The published container includes Deno and ngspice. Its default command starts the HTTP transport on port 3023. Pin the runtime to the GHCR index digest recorded by the post-publication verifier; replace <verified-index-digest> with that digest. Do not treat a mutable version tag as the runtime identity.

docker run --rm \
  -p 127.0.0.1:3023:3023 \
  -v mcp-spice-runs:/ngspice-runs \
  ghcr.io/casys-ai/mcp-spice@sha256:<verified-index-digest> http

The MCP endpoint is http://127.0.0.1:3023/mcp. Native stdio is available from the same image:

docker run --rm -i \
  -v mcp-spice-runs:/ngspice-runs \
  ghcr.io/casys-ai/mcp-spice@sha256:<verified-index-digest> stdio

To run the published JSR module, install ngspice on the host, then use the exact version:

deno run --allow-all jsr:@casys/mcp-spice@0.6.4/server --stdio

For local development:

deno task serve

The normal flow

Submit the exact circuit text, keep the returned SHA-256 reference, then request the analysis using that reference and explicit observables. Simulation responses include the input identity, bounded readings, declared not_checked limits, and a documentary receipt reference.

Details and complete examples live in the repository documentation:

• Installation and transports
• MCP API and content-addressed workflow
• MCP Apps and recorded viewer sessions
• Durable receipts and recovery
• Runtime limits and security model
• Development and release gates

Digital Thread boundary

mcp-spice owns circuit execution and its presentation contracts. Casys Digital Thread may record and display those exact artifacts, but its Workbench remains a read-only projection: it does not choose provider arguments, call ngspice, or reinterpret a documentary result as an engineering decision.

License and citation

The source is licensed under MIT. Citation metadata is available in CITATION.cff.