MCP Server¶

Overview¶

The MCP Server module exposes Python library documentation to AI agents via the Model Context Protocol.

The universal server (lcp serve-all) is the single implementation: agents call resolve_library("package") to load any pip-installed package on the fly, then search and get_symbol to explore it. Resolved manifests are cached as .lcp.json.gz files under ~/.lcp/cache/. The single-manifest command (lcp serve) is deprecated and now wraps the same server, pre-loaded with the manifest.

Key Features¶

lcp serve-all command: single, always-on MCP server for any Python library
Four-tool surface designed around a three-call workflow: resolve_library → search → get_symbol (+ get_overview for orientation)
On-demand library resolution with three-tier fallback: local cache → live scan → remote registry
Live scans run in a disposable child interpreter by default (crash isolation, no import-lock stalls) and can target a different virtualenv via --scan-python
Ranked search with exact import lines in every hit; empty query browses deterministically
Batch get_symbol with inline class-member summaries and exact return-type-to-class resolution
Structured error dicts with stable shape and recovery hints on every failure path
Byte-capped responses (--max-response-bytes) guarding against context blowouts
MultiLibraryIndex: holds multiple libraries simultaneously; with several loaded, tools require an explicit library argument (no silent default)
Usage guidance delivered through the MCP instructions field, reaching agents before any tool call

Documents¶

Architecture - Server structure, index design, error model, caps, tool inventory, and data flow

CLI Commands¶

Command	Purpose
`lcp serve-all`	Start the universal multi-library MCP server (recommended)
`lcp serve <manifest.lcp.json>`	Deprecated: starts the universal server pre-loaded with the manifest

`lcp serve-all` options¶

Option	Default	Description
`--cache-dir PATH`	`~/.lcp/cache/`	Root directory for cached manifests
`--name TEXT`	`lcp-universal`	Server name for MCP identification
`--no-cache`	off	Disable reading from and writing to the local cache
`--registry TEXT`	(none)	Base URL of a remote LCP registry used as a final fallback when local scanning fails
`--expose TEXT`	all packages	Restrict `resolve_library` to these package names (repeatable)
`--preload TEXT`	(none)	Resolve these packages at startup (repeatable)
`--max-response-bytes INT`	`25000`	Byte budget for list-returning tool responses
`--scan-mode [subprocess\\|inprocess]`	`subprocess`	Whether live scans run in a child interpreter or in the server process
`--scan-python TEXT`	server's interpreter	Interpreter whose environment live scans read
`--scan-timeout FLOAT`	`60.0`	Seconds before a subprocess scan is killed

Setup (one-time)¶

pip install lcp

# Claude Code
claude mcp add lcp -- lcp serve-all

# Cursor (.cursor/mcp.json) or Claude Desktop (claude_desktop_config.json)
# { "mcpServers": { "lcp": { "command": "lcp", "args": ["serve-all"] } } }

Key Components¶

Component	Location	Purpose
`LCPIndex`	`src/lcp/mcp_server.py`	In-memory lookup index built from an `LCPDocument`
`MultiLibraryIndex`	`src/lcp/mcp_server.py`	Registry of loaded `LCPIndex` instances with per-library resolution source; enforces explicit-library disambiguation
`LCPServer`	`src/lcp/mcp_server.py`	Dataclass bundling the FastMCP instance, the index registry, and the raw tool callables
`resolve_library_document()`	`src/lcp/mcp_server.py`	Resolves a library via cache, live scan, or remote registry fetch
`scan_package_subprocess()`	`src/lcp/subprocess_scan.py`	Runs a live scan in a child interpreter and classifies failures as typed exceptions
`lcp.scanjson`	`src/lcp/scanjson.py`	Machine-mode scan entry point executed inside the scan interpreter (LCP JSON on stdout, structured errors on stderr, exit-code contract)
`_register_tools()`	`src/lcp/mcp_server.py`	Single registration path for the four tools, shared by all entry points
`create_universal_server()`	`src/lcp/mcp_server.py`	Constructs the universal `LCPServer`
`run_universal_server()`	`src/lcp/mcp_server.py`	Starts the universal server
`create_server()` / `run_server()`	`src/lcp/mcp_server.py`	Deprecated single-manifest wrappers over the universal server
CLI `serve-all` command	`src/lcp/cli.py`	Thin wrapper that calls `run_universal_server()`
CLI `serve` command	`src/lcp/cli.py`	Deprecated thin wrapper that warns and calls `run_server()`

Architecture - Detailed tool inventory, error model, and index design
AI DocGen - Generates the docstrings that make manifests more useful to the MCP server

Last Updated: July 2026 Status: Implemented