Built on Mock Service WorkerInspect and control every API scenario.
MSW Dev Tool turns your existing MSW handlers into runtime controls—so you can inspect requests, debug edge cases, demonstrate states, and verify user flows with confidence.
Inspect
See the registered mock scenarios and their current state
Control
Apply responses, errors, delays, and temporary overrides
Verify
Check the resulting experience in a live application session
Why MSW Dev Tool
Make difficult network states easy to reach.
Reuse your MSW handlers to reproduce any state—from loading to recovery—without changing application code.
A tighter feedback loop
From declared mock to verified experience.
Choose a scenario, inspect the result, and reset it—without building a separate E2E fixture for one API state.
See the workflowBuilt for the whole mock lifecycle
One set of handlers. More useful ways to use them.
MSW Dev Tool complements—not replaces—your test runner and browser automation. It gives developers and agents a deterministic way to place the application in the network state they need before checking what users see.
- Inspect registered mock handlers
- Change responses, latency, errors, or handler availability
- Add and remove temporary handlers without a code change
- Control running sessions through Chrome DevTools Protocol
- Use the same scenario controls in Node and test processes
- Reset every change and return to your declared handlers
Build and verify with the network under control.
Add MSW Dev Tool to an existing MSW setup and start exploring every state your interface needs to handle.
Read the getting started guide