Most Node.js performance content teaches you to avoid eval , use streams instead of buffers, and "don't block the event loop." That's fine advice — and it won't help you when your p99 latency is 2.3 seconds and your CTO is in your Slack DMs.

This is a different kind of article. We start with a realistic API that has real problems, profile it properly, fix each bottleneck with actual code, and measure the delta at every step. No platitudes. Numbers or it didn't happen.

The Benchmark Harness First

Before touching a single line of application code, establish your measurement baseline. Every optimization you make needs a before and after.…