Weights & Biases MCP Server

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

• query W&B Weave traces
• write text and charts to W&B Reports

Available tools

• 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.

• 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.

Usage

Ensure you specify the W&B Entity and W&B Project to the LLM/MCP Client.

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

Installation

uv venv && source .venv/bin/activate
uv pip install -e .

Configuration

1. Create a .env file in the root directory with your Weights & Biases API key:

WANDB_API_KEY=your_api_key_here

Running the Server

Run the server using:

uv run src/mcp_server/server.py

Client Setup

Claude Desktop

    "mcpServers": {
        "weights_and_biases": {
        "command": "uv",
        "args": [
            "--directory",
            "/ABSOLUTE/PATH/TO/PROJECT",
            "run",
            "src/mcp_server/server.py"
        ]
        }
    }

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.