LangSmith MCP Server

What it does

Bridges your AI coding environment directly to LangSmith — LangChain's observability and evaluation platform. Ask your AI agent to fetch trace runs from a project, inspect conversation thread history, manage prompt templates, explore evaluation datasets, and review billing usage, all without leaving your editor.

This is a TypeScript port of the official Python LangSmith MCP Server with 100% functional parity and char-based stateless pagination so responses stay within LLM context limits.

Tools

• get_thread_history — Retrieve message history for a conversation thread with char-budget pagination
• list_prompts — Fetch prompts with optional public/private visibility filter
• get_prompt_by_name — Get a specific prompt template by exact name
• push_prompt — Documentation tool: how to create and push prompts to LangSmith
• fetch_runs — Fetch traces/tool runs/chains from one or more projects with FQL filter support and auto-pagination
• list_projects — List LangSmith projects with optional name/dataset filtering
• list_datasets — Fetch datasets filtered by ID, type, name, or metadata
• list_examples — Read dataset examples with optional version (as_of) and split filters
• read_dataset / read_example — Read a single dataset or example by ID or name
• create_dataset / update_examples — Documentation tools for dataset creation and updates
• list_experiments — List experiment projects for a dataset with latency/cost/feedback metrics
• run_experiment — Documentation tool: how to run evaluations in LangSmith
• get_billing_usage — Fetch org billing usage (trace counts) for a date range with optional workspace filter

Installation

Claude Desktop (~/Library/Application Support/Claude/claude_desktop_config.json):

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

Cursor / Claude Code (.cursor/mcp.json or MCP settings):

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

Optional env vars: LANGSMITH_WORKSPACE_ID (multi-workspace API keys) and LANGSMITH_ENDPOINT (self-hosted or EU region).

Supported hosts

Claude Desktop, Cursor, Claude Code (any stdio-compatible MCP client).