VistaFuzz Fuzzes 7,718 Python APIs Using a Locally-Served Open LLM and Lands 29 Fixed Bugs

arXiv 2608.11744·high signalXBlueskyLinkedInCopy link

VistaFuzz reads API documentation with a locally-served open-source LLM to extract per-parameter constraints AND inter-parameter dependencies, then generates inputs satisfying both. Across 7,718 APIs in twelve Python libraries, inter-parameter relationships appeared in 40.1% of APIs, and disabling dependency resolution collapsed the valid-generation rate on those APIs from above 95% to 31.6-52.8%. It reported 74 issues, 43 confirmed by maintainers and 29 already fixed — a rare case of an LLM testing paper landing real upstream patches without a frontier API key.