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MCP tools

lilctx serve speaks MCP over stdio. Two tools are exposed.

search

Semantic search over the indexed chunks.

Arguments

name type required default meaning
query string yes — Free-form natural-language query.
limit int no 8 Maximum number of hits to return.

A limit of 0 is treated as "use the default."

Returns

A single text block. If there are no hits, it reads (no results). Otherwise, one entry per hit:

score=0.842  /Users/me/notes/runbooks/db.md  (chunk 3)
---
<chunk content>
---

Scores are 1.0 - distance from the LanceDB cosine search — higher is closer. The chunk content is returned verbatim, no truncation, so longer chunks produce longer responses.

list_paths

Returns the configured root paths, one per line. No arguments.

Useful as an introspection call when an agent wants to know what corpus it is searching against. The response prints (no paths configured) when the config has an empty list.

Wiring it into a client

For Claude Code, add an entry like this to your MCP config:

{
  "mcpServers": {
    "lilctx": {
      "command": "lilctx",
      "args": ["serve"],
      "env": {
        "LILCTX_OPENROUTER_API_KEY": "sk-or-..."
      }
    }
  }
}

The env block is how the spawned process gets its API key — Claude Code does not inherit your shell environment. If lilctx is not on PATH, use the absolute path to the binary.

For other MCP clients, the contract is the same: stdio transport, JSON-RPC framing on stdout, all logs to stderr.

Adding a new tool

If you are extending the server, see the "Adding an MCP tool" section in the project's CLAUDE.md. The summary:

  1. Define an args struct with #[derive(Deserialize, JsonSchema)].
  2. Add an async fn inside the #[tool_router] impl LilCtxServer block.
  3. Annotate it with #[tool(description = "...")] — the description is what the agent sees when picking which tool to call. Be specific about what the tool returns; vague descriptions lead to vague tool use.

search in src/mcp.rs is the reference example.