What I learned squeezing the YouTube Data API v3 quota for a side project

TLDR: The default 10,000 unit/day quota will burn through in ~10 naive user requests. Three tricks pulled my per-user cost down 50× and let me ship TubeVocab on the free tier. When I started building TubeVocab — an ESL learning tool that turns any YouTube video into a clickable, vocab-learning interactive transcript — I assumed the YouTube Data API v3 would be the cheap, easy part. "It's Google. It scales. The free tier is generous." That kind of gut feeling. I was wrong. The free tier is genero