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# Regex Tester

Test a regular expression against your own text — the browser's own engine, every match listed, runs in a disposable worker.
The browser’s own RegExp — what you test is what your page ships · every run in a disposable workerInsert sampleClearRegular expressionFlags

Valid flags: d g i m s u v y — no duplicates, and u/v are mutually exclusive.
Text to test the pattern against

No run yet.

- The browser’s own RegExp runs the pattern — no engine substitution, so behavior (including lookbehind, named groups, v-mode set notation) is exactly what your page ships.
- A native RegExp cannot be interrupted, so every run executes in a disposable worker: a pattern that backtracks catastrophically is terminated at the 5 -second deadline and reported — never a frozen tab, never a silent retry in the page. Environments without workers refuse to run it at all.
- Matches list the way matchAll does: the global flag is implied for listing, and zero-length matches advance by one so they are all reported, never dropped.
- Caps, stated before you hit them: 1,000 listed matches (the TRUE total always shows), 32 listed groups per match, 1,000,000 test-text bytes, 1,000 pattern characters.
Nothing in yet

Paste, drop, or type to begin. Everything stays on this device.

the d flag adds [start, end) spans to every group

## Next door in Developer

- [Glob tester](/dev/glob-tester)
- [Semver compare](/dev/semver)
[All developer tools](/dev)

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Canonical HTML: https://nutter.tools/dev/regex-tester
Markdown version: https://nutter.tools/dev/regex-tester/index.md
Plain-text version: https://nutter.tools/dev/regex-tester/index.txt
Agent index: https://nutter.tools/llms.txt