How to profile pure Dart code

Need to profile a Dart script without Flutter? Use the --observe flag to connect to DevTools.

dart run --observe --pause-isolates-on-start <filename>.dart

This will:

1. Start the Dart VM Observatory (a web-based debugger)
2. Pause execution before your code runs
3. Print a URL like http://127.0.0.1:8181/

Open that URL in Chrome, then click “Open DevTools” to access:

• CPU Profiler — see which functions consume the most time
• Memory — track allocations and find leaks
• Timeline — visualise async operations and isolate activity

The --pause-isolates-on-start flag ensures you don’t miss profiling the startup phase. Without it, your code might finish before you connect.

For production profiling, also consider:

# Profile with AOT compilation (closer to real-world performance)
dart compile exe <filename>.dart -o app
./app

This won’t have the Observatory, but gives accurate timings for AOT-compiled code.