Run one unchanged pattern against one unchanged input under baseline and comparison flags, then inspect both match lists.
Submit the example or replace it with your own values. User matching runs only in a disposable browser worker.
Explicit ECMAScript behavior
Flags can change enumeration, case handling, anchors, dot behavior, Unicode parsing, indices, and starting-position rules. Holding pattern and text constant makes the flag set the only intentional variable.
Flags can change enumeration, case handling, anchors, dot behavior, Unicode parsing, indices, and starting-position rules. Holding pattern and text constant makes the flag set the only intentional variable.
Each side is compiled independently and reports its own flags, match count, match boundaries, captures, and truncation state. A syntax error on either flag set fails the comparison instead of silently dropping an option.
Any operation that runs a user pattern is isolated in a disposable Web Worker. Tool Swim terminates that worker after 500 ms, caps patterns at 4 KiB and text at 256 KiB, and never runs user matching on the interface thread.
Pattern, flags, text, replacement, matches, and explanations stay in the current browser tab. The public tool makes no developer API request, stores no preset, and works without an account or telemetry.
