LangSmith MCP Server (TypeScript)

A TypeScript implementation of the Model Context Protocol (MCP) server for LangSmith. This is a full port of the official Python LangSmith MCP Server with 100% functional parity.

Example Use Cases

The server enables powerful capabilities including:

• Conversation History: "Fetch the history of my conversation from thread 'thread-123' in project 'my-chatbot'" (paginated by character budget)
• Prompt Management: "Get all public prompts in my workspace" / "Pull the template for the 'legal-case-summarizer' prompt"
• Traces & Runs: "Fetch the latest 10 root runs from project 'alpha'" / "Get all runs for trace <uuid> (page 2 of 5)"
• Datasets: "List datasets of type chat" / "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"

Quick Start

LANGSMITH_API_KEY=your-key npx langsmith-mcp-server

Available Tools

The LangSmith MCP Server provides the following tools for integration with LangSmith.

Conversation & Threads

Tool Name	Description
get_thread_history	Retrieve message history for a conversation thread. Uses char-based pagination: pass page_number (1-based), and use returned total_pages to request more pages. Optional max_chars_per_page and preview_chars control page size and long-string truncation.

Prompt Management

Tool Name	Description
list_prompts	Fetch prompts from LangSmith with optional filtering by visibility (public/private) and limit.
get_prompt_by_name	Get a specific prompt by its exact name, returning the prompt details and template.
push_prompt	Documentation-only: how to create and push prompts to LangSmith.

Traces & Runs

Tool Name	Description
fetch_runs	Fetch LangSmith 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. All results are automatically paginated by character budget. Always pass limit and page_number.
list_projects	List LangSmith projects with optional filtering by name, dataset, and detail level (simplified vs full).

Datasets & Examples

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

Experiments & Evaluations

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

Usage & Billing

Tool Name	Description
get_billing_usage	Fetch organization billing usage (e.g. trace counts) for a date range. Optional workspace filter; returns metrics with workspace names inline