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Regex Tester

Runs JavaScript regular expressions in an isolated Web Worker with a 300 ms execution limit.

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How Regex Tester works

Runs JavaScript regular expressions in an isolated Web Worker with a 300 ms execution limit.

Try an example

Pattern \d+ against item42 → 42.

Good to know

Potentially expensive expressions are terminated. Max 100,000 text characters, 1,000 pattern characters and 1,000 matches. Flags follow JavaScript regex semantics.

Your privacy

Processing happens on this device for this tool. We do not upload your input, put it in share links or save it to your favourites. Closing this tab discards the working input; downloaded results remain wherever you save them.

When this tool is useful

Use the regex tester to try a pattern against deliberately chosen sample text before adding it to code or a validation rule.

How to use it

  1. Enter a pattern and choose the intended flags.
  2. Add small representative examples, including a case that must not match.
  3. Copy the pattern only after reviewing all matches and the timeout/error message.

Checks before you rely on the result

  • Regular expressions can be ambiguous and expensive; keep patterns bounded and avoid testing untrusted megabytes of text.
  • JavaScript regular-expression syntax and flags apply.
  • A match in a sample does not prove that a production validator is safe or complete.

This page is maintained with the tool implementation and its deterministic tests. If the result looks wrong, report the issue with a non-sensitive example.

Read the Regex Tester instructions

A useful next step

JSON Validator
JSON Formatter
Base64 Decode
Made for clarity. Built to be useful.Report an issue