Regex Tester - Live Matches & Flags | Free Online Tool

A regex tester lets you paste a pattern and sample text, then shows matches and capture groups instantly. Use it to validate patterns before you ship them in code, search, or form validation.

1. Enter a pattern: Paste a regex without surrounding slashes (e.g., \w+@\w+\.\w+).
2. Set flags: Start with g (global). Add i for case-insensitive, m for multiline, u for Unicode.
3. Test text: Paste sample input below; results show live with indices and groups. Copy the clean JSON output if you need to log or share.

• Instant feedback: See matches and errors as you type.
• Capture awareness: View indices and named groups to confirm structure.
• Privacy-first: All parsing runs in your browser; no text is uploaded.

Use case 1: Validate an email-ish pattern

Pattern: ^[\\w.-]+@[\\w.-]+\\.[A-Za-z]{2,}$
Paste a few addresses and confirm only valid ones match.

Use case 2: Extract IDs from URLs

Pattern: /posts/(?<id>\\d+)
Paste several URLs; check that id is captured correctly.

Use case 3: Clean up logs

Pattern: ERROR\\s+(?<code>\\d{3})
Paste log lines and verify the code group.

Basic example

Pattern: cat
Text: concatenate catalog cat
Output shows all cat matches with their indices.

Advanced example

Pattern: (?<user>[A-Za-z0-9_]+)@(example|textavia)\\.com
Flags: gi
Text: multiple email addresses → output lists matches and named group user.

Invalid flag or pattern

If the regex fails to compile, you’ll see Invalid regex: with the JS engine’s message. Fix the pattern or remove unsupported flags.

Empty matches in global mode

Zero-length matches can loop; this tool advances the index automatically. If you see unexpected repeats, adjust the pattern to avoid empty matches.

• Start simple, then add anchors (^, $) and groups.
• Use non-greedy quantifiers *? +? when you want the smallest match.
• Prefer named groups ((?<name>...)) for clarity; check them in the JSON output.
• Turn on m for multiline anchors and u when working with emoji or accented text.

• Format JSON output with the JSON formatter.
• Minify patterns inside code with the JSON minifier if needed.
• Compare two patterns’ outputs with the diff tool.

All regex evaluation happens locally in your browser using JavaScript’s RegExp engine. Your text and patterns are not uploaded or stored.