Pattern is invalid
remove slash delimiters and inspect escaped backslashes, brackets and unsupported PCRE constructs.
JavaScript Regex Tester
Test a JavaScript regular expression against sample text and inspect every match, index and capture group before putting it in code.
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A JavaScript regex tester runs an ECMAScript RegExp pattern against input text and reports matches, positions and capture groups. Enter the pattern without surrounding slashes and select flags such as g, i, m or s; PCRE-only syntax may not work in JavaScript.
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How to use it
Enter the source data: Enter a pattern without leading/trailing slash delimiters, then paste synthetic test text that includes expected matches and non-matches.
Choose the relevant settings: Select flags deliberately. Use g for all matches, i for case-insensitive matching, m/s for line behavior, and type u/y only when the runtime supports the intended semantics.
Review and verify the result: Inspect highlighted matches, indices and capture groups. Add edge cases and long adversarial strings before copying the expression into production code.
Key capabilities
- Runs JavaScript ECMAScript RegExp patterns.
- Supports common flags and typed u/y flags where available.
- Highlights live matches in the sample text.
- Lists match indices and capture groups.
- Includes starter patterns with explicit non-authoritative labeling.
Best use cases
- Debug a front-end validation or extraction pattern.
- Teach capture groups, anchors and flags with visible matches.
- Prepare tested expressions before using find/replace in the scratchpad.
Limits and safety notes
- Regex syntax differs by engine. JavaScript does not implement every PCRE feature, and a pattern that matches examples may still reject valid real-world data or allow invalid data. Avoid using a simple regex as the sole security boundary.
- The core transformation runs in the current browser component. Browser extensions, clipboard history, downloaded files and site-wide diagnostics remain separate exposure points, so never enter production secrets unless you have reviewed the complete environment.
Troubleshooting
Only the first match appears
enable the global flag when multiple non-overlapping matches are required.
Browser freezes on long input
simplify nested quantifiers and ambiguous alternation; add a performance warning and test safeguards.
Frequently asked questions
Should I include /slashes/ around the pattern?
No. Enter only the pattern body in this interface; choose flags separately.
Is this a PCRE regex tester?
No. The target engine is JavaScript ECMAScript RegExp. PCRE recursion, possessive quantifiers, conditionals and other engine-specific syntax may be unsupported.
Are the built-in email or URL patterns fully valid?
They should be described as starter examples only. Real email/URL syntax and product requirements are broader than a compact preset.
Is it safe and private?
The calculation runs in this browser component, but that alone is not a complete privacy guarantee. Use non-production data unless you have also reviewed extensions, clipboard history, downloads and site diagnostics.
Does it work on mobile?
The layout adapts to narrow screens. File selection, camera access, clipboard actions and downloads still depend on the permissions and capabilities of the mobile browser.
Related tools
Use the tool
Build a small test suite of matching, non-matching and adversarial inputs, then copy the expression only after checking the target JavaScript runtime.