rsigma mcp serve

rsigma mcp serve

Run the Model Context Protocol server, exposing the RSigma Sigma toolchain (parse, lint, validate, evaluate, convert, reverse-convert, tune, test exemplars, fields, pipelines) as MCP tools to AI agents such as Cursor and Claude Code.

Synopsis

rsigma mcp serve [OPTIONS]

The server speaks JSON-RPC over stdio: stdin and stdout are the transport, so all human-readable diagnostics go to stderr. Run it under an MCP client rather than interactively.

Description

mcp serve starts a stdio MCP server backed by the same crates the CLI uses. An agent connects, calls tools/list to discover the tool surface, and calls tools with either inline content (e.g. yaml or query) or a file path. Tool outputs are structured JSON: ASTs, lint findings with spans and fix availability, evaluation matches, backend queries, reverse-converted drafts, and field inventories.

For the full tool reference, client setup, and the agentic write-lint-evaluate loop, see the MCP server guide.

The command is gated behind the opt-in mcp Cargo feature: build from source with --features mcp. The prebuilt binaries and Docker image (built with --all-features) include it. See Feature Flags.

Flags

--http, --lint-config, --rules-dir, --allow-sigma-cli, --daemon-url, --daemon-ca, and --allow-operate-writes also resolve from the layered config (mcp section) and the RSIGMA_MCP__* environment layer; the MCP HTTP auth token and the daemon token stay flag/env-only.

The global flags (--log-format, --quiet, …) are accepted but stdout stays reserved for the MCP transport; use --log-format to send structured diagnostics to stderr.

Tools

Plus four read-only resources: rsigma://lint/catalogue, rsigma://ads/schema, rsigma://reference/modifiers, and rsigma://reference/mitre-tactics. See the MCP server guide for the three-tier registration model.

Example: register with Cursor

Add to your mcp.json:

{
  "mcpServers": {
    "rsigma": {
      "command": "rsigma",
      "args": ["mcp", "serve", "--rules-dir", "/path/to/rules"]
    }
  }
}

Streamable HTTP

For remote agents, serve over HTTP instead of stdio:

# Local, loopback (no TLS required)
rsigma mcp serve --http 127.0.0.1:9100

# Authenticated (bearer token), behind a TLS-terminating proxy
RSIGMA_MCP_AUTH_TOKEN=$(openssl rand -hex 32) \
  rsigma mcp serve --http 0.0.0.0:9100 --allow-plaintext

# Native TLS (requires the `daemon-tls` feature)
rsigma mcp serve --http 0.0.0.0:9100 \
  --auth-token "$TOKEN" \
  --tls-cert /etc/rsigma/tls/cert.pem --tls-key /etc/rsigma/tls/key.pem

The endpoint is https?://<addr>/mcp. Plaintext binds on non-loopback addresses are refused unless --allow-plaintext is set (use it when a sidecar proxy terminates TLS). Native TLS reuses the daemon’s rustls loader and is only available when the binary is built with daemon-tls.

Exit codes

See also

• MCP server guide for the full workflow, tool reference, and client setup.
• Feature Flags for the mcp feature.