The BugBash Podcast The Dollar Bet that Fuzzed Figma: Exploding Laptops and UI Reliability with Jonathan Chan
Mar 25, 2026
Jonathan Chan, a former Figma engineer and creator of FuzzMap, built a coverage-guided fuzzer for React UIs. He tells the lunch-bet origin of FuzzMap and why Figma needed faster, reproducible UI testing. He explains the gnarly React instrumentation hacks, state deduplication and visualization, and ideas for extending fuzzing to networks and full-stack scenarios.
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Fuzz Faster By Instrumenting In Process
- Prioritize fuzzing speed: exploring many states quickly finds more bugs even if coverage is imperfect.
- Replace full-browser Selenium runs with in-process instrumentation to dramatically increase fuzz throughput.
States As Initial Snapshot Plus Event Sequences
- FuzzMap instruments conditionals for branch coverage and hooks event handlers to record and replay sequences of UI actions.
- The fuzzer treats a state as initial state plus a sequence of event-handler actions for reproducible exploration.
Bucket Hit Counts To Control State Explosion
- Deduplicate and bucket branch hit counts to collapse the explosion of UI states and focus on meaningful differences.
- Jonathan collapsed loop hit counts to small buckets (e.g., 0/1/2) to avoid treating every list length as a distinct state.