Fathom - Claude Code Telemetry
Local telemetry for Claude Code. Track token spend, tool calls, and session costs in plain JSON on your machine.
Features
- Tracks token usage per session - input, output, and cache tokens
- Records tool call counts and types across every session
- Calculates session cost by model using current Anthropic pricing
- Writes structured JSON to a local directory on your machine
- Zero external network calls - data never leaves your machine
- Works across all Claude Code sessions automatically via hooks
- Output is plain JSON, readable by any tool, script, or spreadsheet
Installation
Fathom is published on npm and installs as a global CLI tool. Run the following command to install it:
npm install -g @aquarium-tools/fathom
Once installed, wire Fathom into Claude Code by adding it to your settings.json hooks. Fathom reads Claude Code's session events and writes a JSON record to a local data directory after each session ends. No account, no API key, and no configuration beyond the hook entry is required.