Regex Tester
Test regular expressions live
Free forever — no sign-up, nothing uploaded. Files never leave your device.
Regex Tester
Test regular expressions live
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Browse filesdocument.pdf
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report.pdf
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About this tool
Write a regex, see matches highlighted in your text, and test flags and capture groups.
The Regex Tester is a live environment for writing and debugging JavaScript regular expressions. As you type, it highlights every match directly in your test text and lists match details, capture groups, and index positions instantly — no test button, no round trips.
It runs the full JavaScript (ECMAScript) regex engine, including named capturing groups, lookahead and lookbehind assertions, the dotAll (s), unicode (u), and indices (d) flags, and Unicode property escapes like \p{L}. Catastrophic-backtracking patterns — the kind that can bring a regex engine to its knees — are detected and paused behind an explicit confirmation, so the tool never freezes your browser without warning.
Flag toggles, a quick-reference panel for common tokens, and per-match capture group breakdowns make it easy to debug even the most tangled patterns. Everything stays in your browser — patterns and test strings are never sent to a server.
Key features
Everything you get with Regex Tester — no premium upsell.
Live match highlighting as you type the pattern
Full JavaScript regex engine with all flags (g, i, m, s, u, d, y)
Numbered and named capture group results with index positions
Supports lookahead, lookbehind, Unicode properties, and advanced constructs
Client-side only — patterns and test strings never leave your browser
Quick-reference panel for common regex tokens and shortcuts
Catastrophic-backtracking guard that pauses suspicious patterns before they can freeze the page
How to use Regex Tester
Follow the steps below to use the tool.
- 1
Enter Your Regex Pattern
Type your regular expression into the pattern field. Surrounding slashes are optional — add them only if you prefer, and the pattern inside is used automatically.
- 2
Set Flags
Toggle flags with the checkboxes: global (g), case-insensitive (i), multiline (m), dotAll (s), unicode (u), indices (d), and sticky (y).
- 3
Provide Test Input
Paste or type your test string into the input area. Matches are highlighted live as you type.
- 4
Review Match Details
Inspect the match results table for full match text, numbered or named capture groups, and character index positions. Use the token quick-reference panel to look up any syntax you need.
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Launch Regex TesterFrequently asked questions
Quick answers before you launch the tool.
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