MobX Spy

Monitor MobX state changes using the spy utility. Start/pause monitoring and filter by event type.

MobX Spy is a DevTools extension that lets you profile and inspect all MobX state changes in your application. It hooks into MobX's spy API to capture actions, reactions, observable updates, and more — then presents the results in a clean, grouped view for easy analysis. How it works MobX Spy uses a profiler-style workflow. Click Record, interact with your app, then click Stop to see the results. Events are captured silently in the background with zero rendering overhead, so your app's performance stays unaffected during profiling. What you can see - Actions, reactions, scheduled reactions, observable updates, additions, removals, splices, errors, and more - Events grouped by name with count badges — instantly see which actions fire most often - Expandable detail panel with a full interactive JSON tree viewer for each event - Color-coded event types and values for quick scanning Key features - Zero-config detection — automatically finds MobX on the page via __mobxGlobals (MobX 6+), with fallbacks for older setups - Source-side filtering — choose which event types to capture; filtering happens before serialization to minimize overhead - Search — filter groups by text across event names and data - Export — save profiling results as a timestamped JSON file for sharing or offline analysis - Resizable columns — adjust the layout to fit your workflow - Keyboard shortcuts — Ctrl/Cmd+K to search, Ctrl/Cmd+S to save, Escape to close panels Detection info The idle screen shows live MobX detection status: which detection method was used, the MobX version, the number of active spy listeners, and an expandable view of window.__mobxGlobals for debugging integration issues. Privacy and security MobX Spy runs exclusively on localhost development URLs (localhost, 127.0.0.1, ::1, 0.0.0.0). It will not activate on production sites. The extension requires zero permissions — no access to browsing history, cookies, or network requests. Supported environments - Chrome 116+ - MobX 4+ (MobX 6+ recommended for zero-config detection) - Applications running on localhost