TL;DR Our checkout API's p99 latency crept up to 2. 1s and nobody could pin down why. I paired with Claude Code to profile it, found two dumb mistakes hiding behind "it's probably the database," and cut p99 to under 900ms in an afternoon.
Source: [Dev.to](https://dev.to/yureki_lab/how-i-used-claude-code-to-cut-my-apis-p99-latency-in-half-mbg)