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Regex Tester

The regex tester runs a JavaScript regular expression against your sample text and shows each match, its position and its capture groups. Matches are highlighted inline so you can see exactly what a pattern does before shipping it.

Options
Test text 0 characters
Matches

Your result will appear here.

Not sure where to start? Use Load example.

Results update automatically and are calculated on your device. Nothing you type is sent to a server.

Runs in your browser. Processing happens entirely in your browser. Nothing you enter is sent to Delimiter.live.

How to use the Regex Tester

  1. Type your regular expression without the surrounding slashes.
  2. Set flags — g for all matches, i for case-insensitive, m for multi-line anchors, s so a dot matches newlines, u for Unicode.
  3. Paste sample text and review the highlighted matches, their positions and capture groups.
  4. Optionally add a replacement to preview a substitution.

Example

Input
Pattern: \d{4}-\d{2}-\d{2}
Text: Due 2026-08-05.
Output
Match 1: 2026-08-05 at position 4

Common use cases

  • Checking a validation pattern against real examples before shipping it.
  • Working out why a log-parsing expression misses certain lines.
  • Building a capture-group replacement to reshape data.
  • Learning regular expressions by experimenting on a live example.

Limitations and things to watch for

  • The engine is the browser JavaScript regular-expression engine. Patterns written for PCRE, Python or .NET may behave differently — there are no possessive quantifiers, no recursion and no inline modifier groups, though lookbehind and named groups are supported in current browsers.
  • A pattern that can match an empty string with the g flag would loop forever, so it is detected and reported instead of run.
  • Catastrophic backtracking is possible with nested quantifiers on long inputs; execution is time-limited and reports a warning instead of freezing the tab.

Frequently asked questions

Which regex flavour does this use?
The JavaScript (ECMAScript) flavour, since it runs in your browser. It supports named capture groups, lookahead and lookbehind, and Unicode property escapes with the u flag, but not PCRE features such as recursion or possessive quantifiers.
Why do I only get one match?
Add the g flag. Without it a regular expression stops at the first match.
How do I use capture groups in the replacement?
Refer to them as $1, $2 and so on, or by name as $<name>. Use $& for the entire match.
Is my test data uploaded?
No. The pattern and the text both stay in your browser.

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