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Regex Tester

Run a regex test online with live match highlights, match counts, indexes, and JSON results.

⌘ Runs in browser ◴ No data stored ⌁ Free

Concept

Regex testing validates matching intent before applying extraction rules

Regex Tester helps you verify pattern intent, flags, and capture behavior in the browser before using it on real data.

For email, URLs, or log formats, define the match intent first, then iteratively adjust the pattern with realistic sample text to reduce false matches.

Run the regex to review match counts, index ranges, and captured groups at once, so you can confirm whether each extracted fragment is truly the target.

This tool follows browser JavaScript RegExp rules. Check against the same assumptions on production input, especially for large strings or complex patterns where performance and false positives are common.

Use case

Use it to validate filter, parse, and format checks before automation or data extraction workflows.

Pattern, flags, and captures

g changes global matching behavior, i/m/s/u affect case, line, dotAll, and Unicode matching, and capture groups define which text parts are extracted.

Result review

Use highlighted matches and JSON output to verify match boundaries and captured values before copying results downstream.

Performance and false positives

Start with small samples, then scale to large inputs to catch slow patterns and unexpected over-matches before deploying.

If matching becomes slow or unstable, simplify the pattern, tighten anchors, and retest with real edge cases.

Regex and test text
Match results
Match count, indexes, and values appear as JSON.

How to use

  1. 1 Enter your regular expression pattern.
  2. 2 Turn on the g, i, m, s, or u flags as needed.
  3. 3 Paste the test string and review the regex test matches.
  4. 4 Adjust the pattern using the error message or highlighted results.

Common use cases

  • Email or ID pattern checks
  • Log string regular expression matching tests
  • JavaScript RegExp g/i/m/s/u flag result comparison

Frequently asked questions

Which regular expression options are supported?

Enter a pattern and test string, then toggle the g, i, m, s, and u flags. When the global flag is enabled, all matches are shown.

How are regex test matches displayed?

Matched text is highlighted, and the result includes the match count plus each match start and end position. You can paste into or clear the test string field.

Which regex syntax does it use?

It uses the browser JavaScript RegExp syntax. Invalid patterns are shown as errors, and without the g flag only the first match is found.

Related workflow

Regex TesterFit the pattern against sample text first to define what should match. → Cron GeneratorIf the pattern runs on a schedule, clarify that timing with a Cron expression. → Diff ViewerAfter changing the pattern or test text, compare how the result changed.