Regex Tester
Test JavaScript regular expressions with live match highlighting, capture group inspection, and a replace mode. Free, in your browser.
Pattern
//
Test text
3 matches
Drop us a line at hello@snaptxt.app, or hanuman@example.com.
Old contact: support@old.co.uk
Not an email: just-text-here.
Capture groups
| # | Match | $1 | $2 | $3 |
|---|---|---|---|---|
| 1 | hello@snaptxt.app | hello | snaptxt | app |
| 2 | hanuman@example.com | hanuman | example | com |
| 3 | support@old.co.uk | support | old.co | uk |
Your text and pattern stay on your device.
Matching uses the browser’s native JavaScript RegExp engine. Nothing is sent to a server.
How to use it
- 1Type your pattern between the / / slashes. Toggle flags below (g, i, m, s, u, y).
- 2Paste your test text on the left. Every match is highlighted in the panel on the right as you type — the count of matches updates live.
- 3If your pattern has capture groups, the table below the matches shows each group's value per match (numbered $1, $2 … and named groups too).
- 4Switch to Replace mode to test a substitution. Use $1, $2 for capture groups, $& for the whole match, and $<name> for named groups.
- 5On Chrome with the Prompt API enabled, describe what to match in plain English and on-device Gemini Nano writes the regex — or hit Explain to get a Gemini Nano breakdown of what your current pattern does.
Common use cases
- Sanity-check a regex before pasting it into a codebase or config file.
- Extract emails, IDs, or URLs out of a chunk of unstructured text using capture groups.
- Rehearse a search-and-replace before running it on a real document.
- Teach or learn regex by watching the highlights update with every keystroke.
- Diagnose why a pattern is matching too much (or too little) with the live match count.
- Skip the regex memorization — describe what to match in English and let on-device AI write it.
Frequently asked questions
- Can the AI write a regex from a description?
- Yes — on Chrome with the Prompt API enabled, a panel above the pattern lets you type something like "match a US phone number with optional country code" and Gemini Nano writes the regex on-device. The /pattern/flags literal is parsed out of the response and loaded straight into the pattern field so you can test it immediately. The whole exchange happens on your machine; nothing is sent to a remote service.
- How does the Explain button work?
- It feeds your current pattern (plus a few sample matches from the test text) to Chrome's on-device Gemini Nano and streams back a 3–6 sentence plain-English description: what it matches, the role of each token, and any backtracking or unicode pitfalls. Only visible on browsers that support the Prompt API.
- Which regex flavor is this?
- ECMAScript / JavaScript regex — the same engine that runs in browsers and Node.js. It's close to PCRE but with a few differences: no possessive quantifiers, no atomic groups, look-behind is supported in modern browsers.
- Is my pattern or test text sent anywhere?
- No. The page uses the browser's built-in RegExp engine. Nothing is uploaded.
- What do the flags do?
- g (global) finds every match instead of just the first. i (case-insensitive). m (multiline) makes ^ and $ match at line breaks. s (dotall) makes . match newlines. u (unicode) enables full Unicode escapes like \p{...}. y (sticky) only matches starting at lastIndex — rarely used outside parsers.
- Why is my regex matching too many things?
- Usually because of greedy quantifiers (* and + match as much as possible). Use the lazy form (*? and +?) to stop at the first satisfying match. Anchors (^, $, \b) also help by tying the pattern to a specific position.
- Capture group $1 is empty — why?
- If your regex contains an alternation (a|b), only the branch that actually matched will fill its groups. Branches that didn't match return undefined for their groups. Either restructure the pattern, or check the named group instead.
- Is there a match limit?
- The page caps at 5,000 matches per pattern to keep the UI responsive. If you're seeing the cap, narrow your pattern.
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