Regex Tester: instructions, examples and limits

What it does

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

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. 1

   Enter a pattern and choose the intended flags.

2. 2

   Add small representative examples, including a case that must not match.

3. 3

   Copy the pattern only after reviewing all matches and the timeout/error message.

How the result is produced

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

Important limits

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

Checks before sharing or relying 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.

Choosing the next step

Treat these tools as a local scratchpad. Validate the format before transforming it, keep secrets out of shared screenshots and remember that a decoded token is not an authenticated token. Use the smallest input that reproduces the problem.