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 generous, but only if you understand how quota math actually works. Most public tutorials skip this. Here's what I learned the hard way. The quota arithmetic nobody puts in the quickstart Default daily quota: 10,000 units . Sounds like a lot. Then you start reading the cost table and realize: search.list — 100 units per call. That's how you find a video by query. videos.list — 1 unit per call. That's how you fetch metadata once you have an ID. captions.list — 50 units . Thumbnails of available subtitles.…