Regex tester with live highlighting
Type a pattern, paste test text, and every match highlights instantly with its capture groups listed in a table below — no Run button, no page reload. A recipe library covers the patterns people reach for constantly (email, URL, Indian mobile number, PIN code, date), and a runaway pattern is caught and stopped automatically instead of freezing the tab.
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This pattern nests quantifiers, a shape that can cause catastrophic backtracking on the wrong input. It runs in a background worker with a 0.8-second watchdog, so it can never freeze this tab — a runaway match is aborted automatically with a warning below.
{{ matchError }}
This pattern took too long against this text (likely catastrophic backtracking) and was stopped automatically. Try a smaller test string or a less nested pattern.
{{ explanation }}
{{ matches.length }} match{{ matches.length === 1 ? '' : 'es' }}{{ truncated ? ' (stopped at 5,000 — very repetitive input)' : '' }}
| # | Match | Groups |
|---|---|---|
| {{ i + 1 }} | {{ m.match }} |
—
${{ gi+1 }}={{ g ?? '—' }}
|
How to use this tool
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Type your pattern and pick flags
g for all matches, i to ignore case, m for multiline, s to let . match newlines.
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Paste test text
Matches highlight live; the table below lists every capture group by number.
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Use a recipe or the replace preview
Click a ready-made pattern from the recipe row, or switch on Replace to preview a substitution with $1-style group references.
Questions people ask
How do I test a regex online?
Type the pattern, paste some sample text, and matches highlight instantly — there is no Run button, and no text is ever sent anywhere; matching happens in a background worker inside your own browser.
What do the g, i and m flags mean?
g finds every match in the text instead of stopping at the first one; i makes matching case-insensitive; m makes ^ and $ match at the start and end of each line rather than only the whole string; s (dotAll) lets . match newline characters too.
What regex matches an Indian mobile number?
^[6-9]\d{9}$ — exactly ten digits, starting with 6, 7, 8 or 9, which is the valid starting-digit range for Indian mobile numbers. It is in the recipe row above, along with PAN, GSTIN, PIN code and a date pattern.
Why does my regex seem to freeze the page?
Nested quantifiers like (a+)+ can cause "catastrophic backtracking" against certain input — the matching engine explores an exponential number of paths trying to fail. This tool runs matching in a Web Worker with an 800ms watchdog, so a runaway pattern is stopped and flagged with a warning instead of ever freezing your tab.
Which regex flavor does this test against?
JavaScript (ECMAScript) — the same engine browsers and Node.js use. Most patterns transfer to other languages' regex flavors with only minor syntax differences (named groups and lookbehind support vary the most between engines).
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Bookmark this page — the tool keeps working offline, and your settings stay in this browser. Built by Dynamb Technologies, who make software for a living.