LangSmith MCP Server for Claude

Overview

The LangSmith MCP Server is the official Model Context Protocol server from LangChain for LangSmith. It gives Claude direct access to your LangSmith workspace — retrieving LLM run traces with FQL filtering, fetching and pushing prompts, browsing evaluation datasets and experiments, and accessing billing usage — through natural language. It runs locally via uvx and is MIT-licensed.

Key capabilities

• Conversation threads — retrieve message history from LangSmith conversation threads with pagination.
• Prompts — list, fetch, and push prompts to and from your LangSmith prompt hub.
• Traces & runs — fetch LangSmith runs (traces, chains, tool calls) with FQL filter support.
• Datasets & examples — list and read evaluation datasets and their examples.
• Experiments — list experiment projects with metrics and evaluation results.
• Billing usage — retrieve organization-level billing usage data.

How it compares

LangSmith's MCP is notable for combining trace retrieval with bidirectional prompt management — you can read production traces and push improved prompts back to the hub in the same session.

Installation

Claude Code

claude mcp add langsmith \
  -e LANGSMITH_API_KEY=your-key \
  -- uvx langsmith-mcp-server

Claude Desktop

{
  "mcpServers": {
    "langsmith": {
      "command": "uvx",
      "args": ["langsmith-mcp-server"],
      "env": {
        "LANGSMITH_API_KEY": "your-langsmith-api-key"
      }
    }
  }
}

Multi-workspace

{
  "env": {
    "LANGSMITH_API_KEY": "your-key",
    "LANGSMITH_WORKSPACE_ID": "your-workspace-id"
  }
}

Custom endpoint (self-hosted LangSmith)

Set LANGSMITH_ENDPOINT to your self-hosted LangSmith URL.

Requirements

• A LangSmith API key (free tier available at smith.langchain.com).
• uv installed (pip install uv or brew install uv).
• An MCP client (Claude Code or Claude Desktop).

Security

• The server only reads (and optionally writes prompts to) your LangSmith workspace.
• Treat LANGSMITH_API_KEY as a secret.
• Trace data may include sensitive LLM inputs and outputs from your applications — use this in trusted environments only.

Source Verification Notes

Verified on 2026-06-18:

• The official repository github.com/langchain-ai/langsmith-mcp-server (MIT) documents the uvx langsmith-mcp-server install command, LANGSMITH_API_KEY and LANGSMITH_WORKSPACE_ID env vars, stdio transport, and the six capability areas (threads, prompts, runs, datasets, experiments, billing).
• LangChain's LangSmith MCP documentation at docs.langchain.com/langsmith/langsmith-mcp-server confirms the server features and setup instructions.
• Claude Code's MCP documentation describes the -e env var injection pattern used above.