LangSmith MCP Server

Use the Model Context Protocol (MCP) server to let language models fetch conversation history, prompts, runs, datasets, experiments, and billing from LangSmith.

Deprecated for LangSmith Cloud—use the LangSmith Remote MCP instead.

LangSmith Cloud now hosts an OAuth-authenticated remote MCP server at https://api.smith.langchain.com/mcp (and https://eu.api.smith.langchain.com/mcp for EU). It exposes the same tool surface as the standalone server documented on this page, but authenticates via OAuth 2.1 with dynamic client registration—no API key, no separate deployment, no header configuration.

The Remote MCP is SaaS-only for now. The standalone server documented below remains the supported path for self-hosted LangSmith deployments and for users who prefer running the server themselves.

The LangSmith MCP Server is a Model Context Protocol (MCP) server that integrates with LangSmith. It lets MCP-compatible clients (for example, AI coding assistants) read conversation history, prompts, runs and traces, datasets, experiments, and billing usage from your LangSmith workspace.

Example use cases

• Conversation history: “Fetch the history of my conversation from thread ‘thread-123’ in project ‘my-chatbot’”
• Prompt management: “Get all public prompts” or “Pull the template for the ‘legal-case-summarizer’ prompt”
• Traces and runs: “Fetch the latest 10 root runs from project ‘alpha’” or “Get all runs for a trace by UUID”
• Datasets: “List datasets of type chat” or “Read examples from dataset ‘customer-support-qa’”
• Experiments: “List experiments for dataset ‘my-eval-set’ with latency and cost metrics”
• Billing: “Get billing usage for September 2025”

Use the server in code or Fleet

• To connect and use remote MCP servers (including this one) in your Python application, see MCP (Model Context Protocol).
• To connect and use this server in Fleet, see Remote MCP servers.

Quickstart (hosted)

A hosted version of the LangSmith MCP Server is available over HTTP, so you can connect without running the server yourself.

• URL: https://langsmith-mcp-server.onrender.com/mcp
• Authentication: Send your LangSmith API key in the LANGSMITH-API-KEY header.

The hosted instance is for LangSmith Cloud. For a self-hosted LangSmith instance, run the server yourself and point it at your endpoint (see Docker deployment).

Example (Cursor mcp.json):

{
  "mcpServers": {
    "LangSmith MCP (Hosted)": {
      "url": "https://langsmith-mcp-server.onrender.com/mcp",
      "headers": {
        "LANGSMITH-API-KEY": "lsv2_pt_your_api_key_here"
      }
    }
  }
}

Optional headers: LANGSMITH-WORKSPACE-ID, LANGSMITH-ENDPOINT (same as in Environment variables).

Available tools

Conversation and threads

Tool	Description
get_thread_history	Get message history for a conversation thread. Uses character-based pagination: pass page_number (1-based) and use the returned total_pages to request more pages. Optional: max_chars_per_page, preview_chars.

Prompt management

Tool	Description
list_prompts	List prompts with optional filtering by visibility (public/private) and limit.
get_prompt_by_name	Get a single prompt by exact name (details and template).
push_prompt	Documentation-only: how to create and push prompts to LangSmith.

Traces and runs

Tool	Description
fetch_runs	Fetch runs (traces, tools, chains, etc.) from one or more projects. Supports filters (run_type, error, is_root), FQL (filter, trace_filter, tree_filter), and ordering. When trace_id is set, results are character-based paginated; otherwise one batch up to limit. Always pass limit and page_number.
list_projects	List projects with optional filtering by name, dataset, and detail level.

Datasets and examples

Tool	Description
list_datasets	List datasets with filtering by ID, type, name, or metadata.
list_examples	List examples from a dataset by dataset ID/name or example IDs; supports filter, metadata, splits, and optional as_of version.
read_dataset	Read one dataset by ID or name.
read_example	Read one example by ID, with optional as_of version.
create_dataset	Documentation-only: how to create datasets.
update_examples	Documentation-only: how to update dataset examples.

Experiments and evaluations

Tool	Description
list_experiments	List experiment (reference) projects for a dataset. Requires reference_dataset_id or reference_dataset_name. Returns metrics (latency, cost, feedback).
run_experiment	Documentation-only: how to run experiments and evaluations.

Billing

Tool	Description
get_billing_usage	Get organization billing usage (e.g. trace counts) for a date range. Optional workspace filter.

Pagination (character-based)

Tools that return large payloads use character-budget pagination so responses stay within a size limit:

• Used by: get_thread_history and fetch_runs (when trace_id is set).
• Parameters: Send page_number (1-based) on each request. Optional: max_chars_per_page (default 25000, max 30000), preview_chars (truncate long strings with ”… (+N chars)”).
• Response: Includes page_number, total_pages, and the page payload. Request more by calling again with page_number = 2, then 3, up to total_pages.
• Benefits: Pages are built by character count, not item count; no cursor or server-side state—just page numbers.

Installation (run locally)

If you prefer to run the server locally (or use a self-hosted LangSmith endpoint), install it and configure your MCP client.

Prerequisites

1. Install uv (Python package installer):

   curl -LsSf https://astral.sh/uv/install.sh | sh
   

2. Install the package:

   uv run pip install --upgrade langsmith-mcp-server
   

MCP client configuration

Add the server to your MCP client config. Use the path from which uvx for the command value.

PyPI / uvx:

{
  "mcpServers": {
    "LangSmith API MCP Server": {
      "command": "/path/to/uvx",
      "args": ["langsmith-mcp-server"],
      "env": {
        "LANGSMITH_API_KEY": "your_langsmith_api_key",
        "LANGSMITH_WORKSPACE_ID": "your_workspace_id",
        "LANGSMITH_ENDPOINT": "https://api.smith.langchain.com"
      }
    }
  }
}

From source (clone langsmith-mcp-server first):

{
  "mcpServers": {
    "LangSmith API MCP Server": {
      "command": "/path/to/uv",
      "args": [
        "--directory",
        "/path/to/langsmith-mcp-server",
        "run",
        "langsmith_mcp_server/server.py"
      ],
      "env": {
        "LANGSMITH_API_KEY": "your_langsmith_api_key",
        "LANGSMITH_WORKSPACE_ID": "your_workspace_id",
        "LANGSMITH_ENDPOINT": "https://api.smith.langchain.com"
      }
    }
  }
}

Replace /path/to/uv, /path/to/uvx, and /path/to/langsmith-mcp-server with your actual paths.

Docker deployment (HTTP-streamable)

You can run the server as an HTTP service with Docker so clients connect via the HTTP-streamable protocol.

1. Build and run:

   docker build -t langsmith-mcp-server .
   docker run -p 8000:8000 langsmith-mcp-server
   

   Use the langsmith-mcp-server repository for the Dockerfile and context.

2. Connect your MCP client to http://localhost:8000/mcp with the LANGSMITH-API-KEY header (and optional LANGSMITH-WORKSPACE-ID, LANGSMITH-ENDPOINT).

3. Health check (no auth):

   curl http://localhost:8000/health
   

For full Docker and HTTP-streamable details, see the LangSmith MCP Server repository.

Deployment overview

Use the hosted MCP server to connect to LangSmith Cloud (smith.langchain.com or eu.smith.langchain.com). To connect to Cloud or self-hosted LangSmith, run the server locally and set LANGSMITH_ENDPOINT. For self-hosted deployments, you can also run the server via the Docker image inside your VPC.

Environment variables

Variable	Required	Description
LANGSMITH_API_KEY	Yes	Your LangSmith API key for authentication.
LANGSMITH_WORKSPACE_ID	No	Workspace ID when your API key has access to multiple workspaces.
LANGSMITH_ENDPOINT	No	API endpoint URL (for self-hosted or custom regions). Default: https://api.smith.langchain.com.

For the hosted server, use the same names as headers: LANGSMITH-API-KEY, LANGSMITH-WORKSPACE-ID, LANGSMITH-ENDPOINT.

TypeScript implementation

A community-maintained TypeScript/Node.js port of the official Python server is available. To run it: LANGSMITH_API_KEY=your-key npx langsmith-mcp-server.

Source and package: GitHub · npm. Maintained by amitrechavia.

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