# Toolweight

> An independent measurement of what each remote Model Context Protocol (MCP) server costs an agent in context-window tokens, before a single tool is called.

Canonical host: https://mydevapp.io

Every MCP server an agent connects to injects its full tool schemas into the model context on every turn. That fixed overhead is paid whether or not any tool is used. Toolweight measures it directly: connect to the server, call tools/list, tokenize each tool definition with the o200k_base encoding, and publish the number.

## Dataset
- Servers probed: 2747 (all remote-capable active entries in the official MCP registry)
- Servers successfully measured: 1085
- Tool definitions tokenized: 16096
- Median server cost: 1421 tokens
- Mean server cost: 4928.72 tokens
- 90th percentile: 11498 tokens
- Heaviest single server: 118285 tokens
- Measurement date: 2026-09-02

## Machine surfaces
- https://mydevapp.io/data.json : full published index and aggregate statistics as JSON
- https://mydevapp.io/api/measure?url=<mcp-server-url> : measure any remote MCP server live, returns JSON
- https://mydevapp.io/index.md : markdown rendering of the index page
- https://mydevapp.io/methodology : how the measurement is performed, and its limits

## Terms
- Context tax: the fixed token cost of having a server's tools registered, paid per model call.
- tools/list: the MCP method that returns a server's tool definitions.
- o200k_base: the byte-pair encoding used for the published token counts.

## License
The published measurements are free to cite and reuse with attribution to Toolweight.