Tools
Small things I wanted while writing the articles. Everything runs in your browser — there is no backend here, nothing is uploaded, and nothing is logged.
System design practiceNeeds your own API key
Answer a real design prompt, then have Claude grade it against a six-part rubric — scores, gaps, and the questions an interviewer would ask next.
Back-of-the-envelope calculatorRuns offline
Turn daily actives and payload size into QPS, storage, bandwidth, and cache size. The numbers that should drive a design, with latencies worth memorising.
Regex backtracking checkerRuns offline
Time a pattern against inputs of growing length to see whether it degrades exponentially. Runs in a worker, so a catastrophic pattern cannot freeze the page.