This is a crosspost of the canonical version on GitHub . 1. Problem I run agent-cost , a small open-source CLI that reads local Claude Code / Codex CLI usage logs and estimates token cost. I wanted documentation for it more trustworthy than a hand-written README: not prose claiming "the reader handles the TTL cache-write breakdown correctly," but claims that each point at the exact test or source line backing them, checked against real git history so the pointer can't silent...