How to view device logs for Detox tests

Viewing device logs for a Detox test lets a developer see what the app and simulator or emulator printed while a specific end-to-end spec was running. The log is useful when Detox reports a matcher, launch, or connection failure but the screen state does not explain the app-side error.

Detox records device logs through its artifact system. The --record-logs option writes log files under the artifact root selected with --artifacts-location, alongside screenshots or videos only when those separate artifact options are also enabled.

A focused rerun keeps the artifact folder limited to one spec and one device target. An ios.sim.debug Jest configuration keeps the log paths readable; use the matching Android or iOS configuration from the project.

1. Run the affected Detox spec with device log recording enabled.

   $ npx detox test --configuration ios.sim.debug e2e/login.e2e.js --record-logs all --artifacts-location artifacts/device-logs
   detox[run_tests] ios.sim.debug
   FAIL e2e/login.e2e.js
     Login
       x opens dashboard after sign in (9.3 s)
   
   DetoxRuntimeError: Test Failed: No elements found for matcher: by.id("dashboardTitle")
   Artifacts saved to artifacts/device-logs/ios.sim.debug.2026-06-18 13:15:20Z

   Use --record-logs all for a focused rerun so a log remains even if the failure does not reproduce. Use --record-logs failing for routine CI storage.

2. List the saved log files under the artifact root.

   $ find artifacts/device-logs -name "*.log"
   artifacts/device-logs/ios.sim.debug.2026-06-18 13:15:20Z/startup.log
   artifacts/device-logs/ios.sim.debug.2026-06-18 13:15:20Z/Login/test.log

   startup.log covers app launch and early device output. test.log covers the device output captured while the named test was running.

3. Open the per-test device log.

   $ cat "artifacts/device-logs/ios.sim.debug.2026-06-18 13:15:20Z/Login/test.log"
   13:15:24.102 ExampleApp[9312] LoginScreen mounted
   13:15:25.441 ExampleApp[9312] API POST https://api.example.net/session -> 401
   13:15:25.448 ExampleApp[9312] LoginScreen rendered authentication error
   ##### snipped #####

   Open the log for the failing test folder first. That file usually contains the app-side error closest to the Detox assertion failure.

4. Open the startup log when the app fails before the test body runs.

   $ cat "artifacts/device-logs/ios.sim.debug.2026-06-18 13:15:20Z/startup.log"
   13:15:20.871 ExampleApp[9312] Launching with Detox session
   13:15:21.036 ExampleApp[9312] Loaded launch arguments
   13:15:21.284 ExampleApp[9312] Detox ready

   Check startup.log for launch arguments, early native crashes, cleartext-network blocks, and app initialization errors.

5. Search the per-test log for the app-side signal that matches the Detox failure.

   $ grep -n "LoginScreen" "artifacts/device-logs/ios.sim.debug.2026-06-18 13:15:20Z/Login/test.log"
   1:13:15:24.102 ExampleApp[9312] LoginScreen mounted
   3:13:15:25.448 ExampleApp[9312] LoginScreen rendered authentication error

   Keep the matching test.log with the failed test output when filing an app bug. Add screenshots or video only when the log does not show the visible state clearly.
   Related: How to save Detox test artifacts
   Related: How to capture screenshots in Detox tests
   Tool: Application Log Pattern Analyzer