Regex Tester. Test ECMAScript regular expressions with exact global, Unicode, capture, index, and replacement behavior plus conservative backtracking-risk refusal.
A quick decision brief for this specific tool
Test String plus Pattern Library, Regular Expression, Flags, Replace Pattern (optional)
Match Results
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Test one ECMAScript regular expression with exact flag semantics, bounded input, capture and replacement evidence, while refusing common catastrophic-backtracking shapes and disclosing that heuristic screening is not a sandbox.
Confirm first-versus-global behavior, indices, groups, Unicode and replacement semantics in the same engine family as production.
Enter pattern/test text, set exact flags, inspect matches and groups, toggle replacement and save the record.
Can reproduce the result without assuming PCRE, Python or Java compatibility.
Prevent a browser demo from being treated as a safe regex execution service.
Test known dangerous structures, confirm conservative refusal, document length/resource bounds, and require a terminable isolated production engine.
No untrusted pattern is approved solely because this page returned quickly.
Verify zero-length iteration across surrogate pairs and operate every flag/result control without visual-only meaning.
Test emoji with `gu`, read positions and warnings, copy evidence and use Project save.
Gets finite, correctly indexed results and named controls with no hidden safety claim.
Outputs and checklists are planning aids. Review the linked current authorities and the records, terms, instructions, and requirements that apply to your exact situation before a consequential decision.
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Patterns are evaluated using JavaScript's RegExp engine (ECMAScript standard). Syntax follows JS conventions: \d for digits, \w for word characters, ^ and $ for anchors, and (?...) for groups and lookaheads.
The available flags are g (global), i (case-insensitive), m (multiline anchors), s (dotAll), and u (Unicode). With g off, matching and replacement stop after the first match; with g on, results are capped at 500.
Quantifiers (*, +, ?, {n,m}) control how many times a preceding element repeats. By default they are greedy (match as much as possible). Append ? for lazy matching (match as little as possible).
Updated: July 2026
Use a bounded pattern to find email-like substrings for later application-level validation; a regex match does not prove deliverability, ownership, or standards compliance.
→ Highlights candidate substrings and records exact match indices
Use a capture group to pull ISO dates (YYYY-MM-DD) from server log lines.
→ Group 1 captures each date match
Test a pattern that accepts common US phone formats with optional country code and separators.
→ Matches (555) 123-4567 and +1-555-123-4567
Characters like . * + ? [ ] ( ) { } | \ ^ $ have special meaning. Use \ to match them literally. A dot (.) matches any character; \. matches a literal period.
Python, Java, PCRE, and JavaScript differ on features like lookbehind support and word boundaries. Test with the engine your production code uses — this tool uses JavaScript RegExp.
Build and debug regular expressions without leaving your browser. Enter a pattern and test string to see all matches, capture groups, and match indices highlighted in real time — essential for validation, parsing, and search-and-replace tasks.
