FaultLab

Controlled network and JSON failure injection for local web application testing.

FaultLab is a local-first Chrome Side Panel for testing how web applications behave when APIs, networks, or response data fail. Use FaultLab to test real applications with controlled failure scenarios: - return selected HTTP error responses; - add request latency; - simulate offline requests; - trigger bounded request timeouts; - throttle tab-level network bandwidth; - remove, nullify, empty, or type-mismatch JSON response fields; - configure built-in scenarios or create custom scenarios with multiple rules; - limit how many times a fault is applied; - record request and navigation metadata for one selected tab; - monitor local console, runtime, Promise, and failed-network errors; - group repeated errors in Error Observatory; - add investigation notes and optional screenshot evidence; - export a local Markdown report or print a local PDF report. FaultLab is designed for developers and QA engineers testing applications they own or are authorized to test. It helps you find fragile error handling before your users do. All runtime state stays local in the browser. FaultLab does not require an account, backend, analytics service, or team synchronization. Scenarios, recorder data, findings, notes, and screenshots are stored locally. Request bodies, form values, and matched response bodies are not persisted. Matched response bodies may be read temporarily in memory when JSON response mutation is active. FaultLab operates on one selected browser tab at a time. Chrome's debugger permission is used to pause network requests, apply controlled failures, inspect selected response bodies for local JSON mutation, throttle traffic, and observe selected error events. Review URLs, error messages, source paths, and screenshots before sharing exported reports because application data may contain sensitive information.