Axonix Tools

Regex Tester Online

Powerful regex tester online. Test, debug, and visualize your regular expressions with real-time highlighting and validation.

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Test String

Match Preview

0 Matches Found
The quick brown fox jumps over the lazy dog

Built With Care

“This tester uses your browser's native JavaScript RegExp engine (V8/SpiderMonkey) for bit-perfect accuracy. Results match exactly what your production code will produce — no approximation, no translation layer.”

Regex Tester

Type a regex and test it against sample text. Matches highlight live with index tooltips, and invalid patterns show an instant error message. Supports JavaScript regex syntax with flags, presets, and instant error detection.

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How to Use Regex Tester
  • 1Type or paste your regular expression pattern into the 'Regular Expression' input field.
  • 2Add optional flags like 'g' (global) or 'i' (ignore case) in the 'Flags' box.
  • 3Enter the text you want to test in the 'Test String' area.
  • 4Matches will be highlighted in real-time in the 'Match Preview' panel.
  • 5Hover over any highlighted match to see its specific index within the string.
  • 6Use a preset (email, URL, date, phone) to get started with a proven pattern.
Key Features
  • Live Highlighting: See match results instantly as you type your pattern or text.
  • Error Validation: Detailed error messages for invalid regex syntax to help you debug.
  • Common Presets: Quick-load samples for email, URL, date, and phone number validation.
  • Flag Support: Full support for JS regex flags (g, i, m, s, u, y).
  • Browser-native RegExp engine: Accurate pattern matching identical to your production code.
  • Match Index Display: Hover any match to see its exact position in the test string.

Regex Tester Specs

Limits

  • JavaScript flavor of regex only
  • Test strings up to practical paste size

Formats

  • Output: match list, groups, highlights
  • Flags: g, i, m, s, u

Defaults

  • Global flag on
  • Highlight matches inline

How it works

  • JavaScript RegExp engine

Honest caveats

  • PCRE features (lookbehind supported in modern JS) — atomic groups are not
  • ReDoS risk on pathological patterns

Real Ways People Use This

Pattern Validation

Verify that your regex patterns match the expected input before deploying them in code.

Form Validation Testing

Test email, phone, and URL validation patterns against edge cases like empty strings and long inputs.

Data Extraction

Build and refine regex patterns for extracting specific data from text strings.

Log & Error Parsing

Develop patterns for extracting timestamps, error codes, and IP addresses from application logs.

Important Notes
  • Regex patterns that work in JavaScript may behave differently in other engines (PCRE, RE2, .NET).
  • Overly broad patterns can produce false positives and expensive backtracking on long strings.
  • Escaping rules differ between regex literals and string-based patterns in application code.
Quick Checklist
  • 1Test pattern against both valid and intentionally invalid sample inputs.
  • 2Verify flags (`g`, `i`, `m`, etc.) match your production parser behavior.
  • 3Benchmark tricky patterns on long input before deploying to hot paths.

Questions That Usually Come Up

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