Rewriting a Node.js service in Go with agents
TLDR Dev
Checkly rewrote a Node.js JavaScript service in Go using Claude Code, with a black-box test harness that compared outputs against production data for a service handling 92 million daily messages. The rollout reported zero incidents and surfaced a production-vs-test queue mismatch due to incomplete dependency modeling. As a result, Checkly improved how dependencies are represented in testing to keep behavior aligned after the language switch.
Why it matters
Checkly used Claude Code to rewrite a JavaScript service (92 million daily messages) in Go, guided by a black-box test harness comparing against production data. The rewrite launched with zero incidents and large resource reductions, while a production-vs-test queue mismatch highlighted the need to model every dependency accurately.