Regex Tester – Test Regex Online (Free Tool)

Regex Tester evaluates a regular expression against sample text and shows every match with its capture groups, position, and length. Use it to author and debug regexes for validation, parsing, or search-and-replace before pasting them into your code. Matching uses the browser's RegExp engine so the behaviour exactly matches what your JavaScript runtime will see.

• Your data stays private — all processing happens locally in the browser
• No telemetry, no tracking pixels, no third-party scripts
• Open-and-go: bookmark the page once and never look for an alternative
• No telemetry on the tokens, payloads, or code you paste in
• Built for developer workflows: copy-friendly output, syntax-aware highlighting where useful

1. Paste the input you want to process
2. Adjust any optional flags or formatting settings
3. Run the conversion — everything happens locally in your browser
4. Copy the output for use in your project

• Authoring form validation patterns for email, phone, zip
• Building log-parsing regexes that extract timestamps and message bodies
• Designing search-and-replace patterns for code-editor refactors
• Verifying captured groups in API URL routing rules
• Teaching regex syntax — instant feedback makes anchors and quantifiers click

My regex matches in the tester but not in my code.

Check the flags. The tester supports g, i, m, s, u — make sure your code uses the same flags. Also verify your code escapes backslashes correctly (\\d in a string literal).

Pattern is "too greedy" and matches more than expected.

Use a non-greedy quantifier (.*? instead of .*), or constrain with character classes ([^"]* between quotes instead of .*).

Catastrophic backtracking — tester hangs.

Patterns with nested quantifiers like (a+)+ can blow up on certain inputs. Refactor to avoid nested quantifiers or use possessive matching where available.