The problem
The network panel shows requests and query devtools show the cache, but neither tells you which fields of a response the app actually reads. Over-fetching stays invisible until the page is slow.
What I built
A dependency-free browser SDK that patches fetch and XMLHttpRequest, wraps responses in a tracking proxy and records the shape of what was read, never the values. A Next.js 16 app on Postgres and Drizzle ingests those events and turns them into findings per endpoint.
Outcome
Live at apiheron.com, with the SDK published as @apiheron/sdk on npm under MIT. Its first test subjects were my own apps, where it found fields that had been shipped for months without a single read.
Stack
- Next.js
- TypeScript
- PostgreSQL
- Drizzle
- SDK