Weights & Biases MCP Server

A Model Context Protocol (MCP) server for querying Weights & Biases data. This server allows a MCP Client to:

• query W&B Models runs, sweeps, artifacts and registry
• query W&B Weave traces, evaluations and datasets
• write text and charts to W&B Reports
• query wandbot, the W&B support bot, for general W&B feature questions

Installation

We provide a helper utility for easily installing the Weights & Biases MCP Server into applications that use a JSON server spec. Please first install uv, typically by running curl -LsSf https://astral.sh/uv/install.sh | sh on your machine or running brew install uv on your mac.

From there, the add_to_client helper will add or update the required mcp json for popular MCP clients below - inspired by the OpenMCP Server Registry add-to-client pattern

Cursor

Cursor project (run from the project dir):

uvx --from git+https://github.com/wandb/wandb-mcp-server add_to_client .cursor/mcp.json && uvx wandb login

Cursor global (applies to all projects):

uvx --from git+https://github.com/wandb/wandb-mcp-server add_to_client ~/.cursor/mcp.json && uvx wandb login

Windsurf

uvx --from git+https://github.com/wandb/wandb-mcp-server add_to_client ~/.codeium/windsurf/mcp_config.json && uvx wandb login

Claude Desktop:

First ensure uv is installed, you might have to use brew to install depite uv being available in your terminal:

brew install uv

then:

uvx --from git+https://github.com/wandb/wandb-mcp-server add_to_client ~/Library/Application\ Support/Claude/claude_desktop_config.json && uvx wandb login

Manual Installation

If you don't want to use the helper above, add the following to your MCP client config manually:

{
  "mcpServers": {
    "wandb": {
      "command": "uvx",
      "args": [
        "--from",
        "git+https://github.com/wandb/wandb-mcp-server",
        "wandb_mcp_server"
      ]
    }
  }
}

Runing from Source

Run the server from source using:

wandb login && uv run src/wandb_mcp_server/server.py

Available W&B tools

wandb

• query_wandb_gql_tool Execute an arbitrary GraphQL query against wandb experiment tracking data including Projects, Runs, Artifacts, Sweeps, Reports, etc.

Weave

• query_weave_traces_tool Queries Weave traces with powerful filtering, sorting, and pagination options. Returns either complete trace data or just metadata to avoid overwhelming the LLM context window.

• count_weave_traces_tool Efficiently counts Weave traces matching given filters without returning the trace data. Returns both total trace count and root traces count to understand project scope before querying.

W&B Support bot

• query_wandb_support_bot Ask wandbot, our RAG-powered support agent for general help on how to use Weigths & Biases products and features. Powered by the W&B documentation.

Saving Analysis

• create_wandb_report_tool Creates a new W&B Report with markdown text and HTML-rendered visualizations. Provides a permanent, shareable document for saving analysis findings and generated charts.

General W&B helpers

• query_wandb_entity_projects List the available W&B entities and projects that can be accessed to give the LLM more context on how to write the correct queries for the above tools.

Usage tips

Provide your W&B project and entity name

LLMs are not mind readers, ensure you specify the W&B Entity and W&B Project to the LLM. Example query for Claude Desktop:

how many openai.chat traces in the wandb-applied-ai-team/mcp-tests weave project? plot the most recent 5 traces over time and save to a report

Avoid asking overly broad questions

Questions such as "what is my best evaluation?" are probably overly broad and you'll get to an answer faster by refining your question to be more specific such as: "what eval had the highest f1 score?"

Ensure all data was retrieved

When asking broad, general questions such as "what are my best performing runs/evaluations?" its always a good idea to ask the LLM to check that it retrieved all the available runs. The MCP tools are designed to fetch the correct amount of data, but sometimes there can be a tendency from the LLMs to only retrieve the latest runs or the last N runs.

Troubleshooting

Error: spawn uv ENOENT

If you encounter an error like this when starting the MCP server:

Error: spawn uv ENOENT

This indicates that the uv package manager cannot be found. Fix this with these steps:

1. Install uv using the official installation script:

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

2. If the error persists after installation, create a symlink to make uv available system-wide:

   sudo ln -s ~/.local/bin/uv /usr/local/bin/uv

3. Restart your application or IDE after making these changes.

This ensures that the uv executable is accessible from standard system paths that are typically included in the PATH for all processes.

Testing

The tests include a mix of unit tests and integration tests that test the tool calling reliability of a LLM. For now the integration tets only use claude-sonnet-3.7.

####Set LLM provider API key

Set the appropriate api key in the .env file, e.g.

ANTHROPIC_API_KEY=<my_key>

####Run 1 test file

Run a single test using pytest with 10 workers

uv run pytest -s -n 10 tests/test_query_wandb_gql.py

####Test debugging

Turn on debug logging for a single sample in 1 test file

pytest -s -n 1 "tests/test_query_weave_traces.py::test_query_weave_trace[longest_eval_most_expensive_child]" -v --log-cli-level=DEBUG