Registry / llm-agents / langsmith-mcp-server

langsmith-mcp-server

library0.1.1jsnpmunverified

The `langsmith-mcp-server` package provides a TypeScript implementation of the Model Context Protocol (MCP) server, designed to integrate with LangSmith, a platform for developing, evaluating, and monitoring large language model (LLM) applications. This server acts as a gateway, exposing LangSmith's rich data (including conversation history, prompts, traces, runs, datasets, and experiments) through a standardized protocol. It offers functional parity with its official Python counterpart and is currently at version 0.1.7, indicating active development with potential for non-stable API changes before a 1.0 release. The package is primarily intended to be run as a standalone service, leveraging environment variables for configuration, though it also provides programmatic interfaces for embedding or advanced customization. Its key differentiators include native TypeScript support, a comprehensive set of tools for accessing LangSmith data, and standardized char-based pagination for large data fetches.

llm-agents ai-ml

npm install langsmith-mcp-server

package ↗homepage ↗

INSTALL

IMPORT

SIG · LANGSMITH-MCP-SERV

langsmith-mcp-server

llm-agentsjavascriptv0.1.1

Install

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Import

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Disk

—

Pass rate

0/ 6

Env Coverage0 / 6

glibc

18–22

musl

18–22

Install & Compatibility

Where this runs

tested against v? · npm install

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

node 18–226 runs

build_error

glibc

node 18–226 runs

build_error

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

startServer

✓ import { startServer } from 'langsmith-mcp-server'

✗ const { startServer } = require('langsmith-mcp-server')

Primarily an ESM library. Use named imports. The `startServer` function initializes and runs the MCP server.

LangSmithMcpServer

✓ import { LangSmithMcpServer } from 'langsmith-mcp-server'

✗ import LangSmithMcpServer from 'langsmith-mcp-server'

The main class for programmatic server instantiation. Named import is required.

ServerOptions

✓ import type { ServerOptions } from 'langsmith-mcp-server'

✗ import { ServerOptions } from 'langsmith-mcp-server'

Import the `ServerOptions` interface using `import type` for type-only imports in TypeScript.

Demonstrates how to programmatically start the LangSmith MCP Server, setting configuration options like port and the LangSmith API key from environment variables.

import { startServer } from 'langsmith-mcp-server'; // Ensure LANGSMITH_API_KEY and other environment variables are set // or passed via options if starting programmatically. // Example: process.env.LANGSMITH_API_KEY = 'your_key_here'; async function runMcpServer() { try { console.log('Starting LangSmith MCP Server...'); const server = await startServer({ port: process.env.PORT ? parseInt(process.env.PORT) : 8000, langsmithApiKey: process.env.LANGSMITH_API_KEY ?? '' // Recommended: use env var }); console.log(`LangSmith MCP Server running on port ${server.address()?.port}`); // Keep the server running until explicitly stopped // For a real application, you might want graceful shutdown handling } catch (error) { console.error('Failed to start LangSmith MCP Server:', error); process.exit(1); } } runMcpServer();

langsmith-mcp --version

Debug

Known issues

breakingAs the package is pre-1.0 (currently 0.1.7), its API and behavior are subject to change without strict adherence to semantic versioning. Breaking changes may occur in minor or patch releases.

fix

Always review release notes when updating and consider pinning to exact patch versions in production environments.

affects: <1.0.0

gotchaData fetching tools like `get_thread_history` and `fetch_runs` utilize character-based pagination instead of item-based pagination. Users must account for `max_chars_per_page` and `total_pages` when iterating through results, which differs from typical array-based pagination.

fix

Refer to the documentation for each tool regarding `page_number`, `max_chars_per_page`, `preview_chars`, and `total_pages` to correctly paginate through results.

affects: >=0.1.0

gotchaThe server requires Node.js version 18 or higher. Running with older Node.js versions will result in startup failures or unexpected behavior.

fix

Upgrade your Node.js environment to version 18 or newer using a version manager like `nvm` or by installing a recent LTS release.

affects: <18.0.0

gotchaThe `LANGSMITH_API_KEY` environment variable is essential for authentication with LangSmith. Failure to set it will prevent the server from accessing LangSmith resources and can lead to authentication errors or failures to fetch data.

fix

Ensure `LANGSMITH_API_KEY` is set in your environment before starting the server, e.g., `LANGSMITH_API_KEY=your_key npx langsmith-mcp-server` or `process.env.LANGSMITH_API_KEY = '...'` for programmatic use.

affects: >=0.1.0

Errors

Common errors & fixes

Error: LANGSMITH_API_KEY is not set. Please set the LANGSMITH_API_KEY environment variable.

The server failed to find the required LangSmith API key for authentication.

fix

Set the `LANGSMITH_API_KEY` environment variable before running the server, e.g., `export LANGSMITH_API_KEY='your-secret-key'` or pass it in the `ServerOptions` when starting programmatically.

TypeError: 'fetch' is not a function

This error typically indicates that the Node.js version being used is too old and does not natively support the `fetch` API.

fix

Upgrade your Node.js environment to version 18 or higher. Node.js 18+ includes the native `fetch` API which this server relies upon.

Error: listen EADDRINUSE: address already in use :::8000

The default port (8000) or a specified port is already being used by another process on your system.

fix

Stop the conflicting process, or specify a different port for the LangSmith MCP Server using the `PORT` environment variable (e.g., `PORT=8001 npx langsmith-mcp-server`) or in programmatic `ServerOptions`.

Upgrade

Version history

0.1.1latest on npm

Audit

Dependencies

No dependency data recorded yet.

Agent activity

21 hits · last 30 days

node

OpenAI (training)

Resources

packagehttps://www.npmjs.com/package/langsmith-mcp-server ↗

homepagehttps://langsmith.com ↗