How I Cut a 2.1 MB JavaScript Bundle to 890 KB With Claude Code

TL;DR

I had a 2.1 MB initial JavaScript bundle and a Lighthouse performance score of 41 on mid-range Android. I used Claude Code as a measurement-driven "perf detective" instead of asking it to "make the app faster," and got the bundle down to 890 KB in about four working sessions. The trick was giving the agent real build artifacts to read, forcing one change per measurement, and then locking the wins in with lint rules and a CI budget so they couldn't rot. 🚀

The Problem

Our dashboard app had grown for three years. Nobody deliberately made it heavy — it just accumulated. The numbers as of the day I started:

2,148 KB of initial JavaScript (gzipped: 612 KB)

How I Cut a 2.1 MB JavaScript Bundle to 890 KB With Claude Code

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