langmcp

Read-only MCP server for inspecting LangGraph checkpoints, thread state, and long-term memory.

LangMCP helps you answer the debugging question that traces do not always answer:

What is actually saved in my LangGraph persistence layer right now?

It is not a generic SQL MCP. It uses LangGraph-native checkpointer and store APIs, connects through named profiles, and keeps database credentials out of tool arguments.

When a stateful agent behaves strangely, the problem is often not only the prompt. It might be the checkpoint it resumed from, the user ID in configurable state, the store namespace used for memory, or an oversized message history.

LangMCP gives MCP clients such as Cursor and Claude Desktop a safe inspection surface for those questions.

Use LangSmith for traces, LangGraph Studio for visual graph workflows, and LangMCP when you want an assistant in your editor to inspect persisted state through a narrow read-only interface.

- Profile-based config with environment variable expansion.
- Read-only enforcement in v0.1.
- Secret redaction in health checks and error output.
- PostgreSQL, SQLite, and Redis checkpointer inspection.
- PostgreSQLPostgresStorelong-term memory inspection.
- MCP tools for threads, checkpoints, store data, and analysis.
- MCP resources for stable readable state URIs.
- MCP prompts for repeatable debugging workflows.
- Pagination and truncation for large responses.

LangMCP supports Python 3.11 and 3.12. The repository includes a.python-versionfile set to Python 3.12.

Copy the example config and environment files:

cp examples/langmcp.example.toml langmcp.toml cp .env.example .env

POSTGRES_URI=postgresql://READONLY_USER:READONLY_PASSWORD@HOST:5432/DB_NAME LANGMCP_READ_ONLY=true

LangMCP loads.envautomatically when present. Existing shell environment variables take precedence.

[defaults] profile = "dev" read_only = true max_response_chars = 250000 [profiles.dev] checkpointer = "${POSTGRES_URI}" store = "${POSTGRES_URI}" [profiles.local_sqlite] checkpointer = "sqlite:///./.langgraph/checkpoints.db" [profiles.local_redis] checkpointer = "redis://localhost:6379/0"

- LANGMCP_CONFIG
- LANGMCP_PROFILE
- LANGMCP_READ_ONLY
- POSTGRES_URI
- LANGMCP_CHECKPOINTER_URI
- LANGMCP_STORE_URI

The doctor command checks connectivity, backend types, setup status, package versions, and redacts sensitive URI fields.

{ "mcpServers": { "langmcp": { "command": "uvx", "args": ["langmcp[all]", "serve", "--config", "ABSOLUTE_PATH_TO_LANGMCP_TOML"], "env": { "LANGMCP_READ_ONLY": "true", "POSTGRES_URI": "postgresql://READONLY_USER:READONLY_PASSWORD@HOST:5432/DB_NAME" } } } }

Once connected through MCP, ask your assistant:

Use LangMCP to summarize thread THREAD_ID and check whether user memory exists for USER_ID.

Compare checkpoint CHECKPOINT_A and CHECKPOINT_B for thread THREAD_ID. Tell me what changed.

Analyze whether thread THREAD_ID is carrying too much context.

Investigate a possible memory gap for thread THREAD_ID and user USER_ID.

All tools accept optionalprofileunless noted. Responses includeprofile,truncated, and pagination fields where applicable.

Resources expose readable state through stable MCP URIs.

For multi-part namespaces, prefer theget_store_itemtool if your MCP client treats/as a path separator inside resource parameters.

Prompts package repeatable investigations.
- Tools accept profile names, not raw DSNs.
- read_only=trueis enforced in v0.1.
- Use a read-only PostgreSQL user for shared environments.
- Passwords are redacted inhealth_checkand CLI output.
- Redis thread discovery usesSCANwith limits. Avoid broad scans on very large instances.
- Commitexamples/langmcp.example.tomland.env.example, not reallangmcp.tomlor.envfiles.

uv pip install -e ".[all,dev]" ruff check . pytest tests/unit -v

Integration tests use local Docker services:

docker compose -f docker-compose.test.yml up -d POSTGRES_URI=postgresql://langgraph:langgraph@localhost:5442/langgraph \ REDIS_URI=redis://localhost:6379/0 \ pytest tests/integration -v -m integration

Use the local test values fromdocker-compose.test.yml. They are for Docker integration tests only.

- LangGraph Agent Server adapter.
- HTTP transport with team auth.
- Vector store inspection tools.
- Carefully scoped write workflows such asupdate_thread_stateandresume_thread.

Issues and pull requests are welcome. SeeCONTRIBUTING.md.

Persistent memory MCP server for Claude — store decisions, code, and knowledge across sessions.