Regex Tester with Explanation

Regex Tester with Explanation

Test regular expressions live with highlighted matches and groups in your browser, no account.

Flags
Try:

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Cheat sheet

            
          

          
Click a token to insert it at the cursor.

        
        
      

    


    

      
How it works

      
      
    
        
  1. Type a pattern and flags. Write a JavaScript regular expression, toggle g, i, m, s, u or y, or start from a ready pattern or the cheat sheet.
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  2. Paste your test text. Matches light up as you type, the match list shows every index, length and group, and the explanation spells out each token.
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  3. Replace and take it with you. Write a replacement with $1 or $<name>, then copy or download the result, or copy the pattern as a /literal/.
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Questions, answered

      
      

        Is my pattern or test text uploaded anywhere?
        
No. Regex Tester with Explanation runs entirely in your browser. Your pattern and text stay in memory on your device, are matched by your browser's own engine, and are never sent to a server, so pasting real log lines is safe. The share link keeps the pattern after the # sign, a part of the address browsers never send to any server. You can disconnect from the internet and it keeps working.

      

      

        Which regex flavor does it test?
        
JavaScript (ECMAScript), the one used by browsers and Node.js, because matching runs on the built-in RegExp engine. PCRE-only features such as possessive quantifiers, atomic groups, recursion or \A and \Z are not supported and show an error. Lookbehind works in current browsers but not in some older Safari versions.

      

      

        What happens if my pattern is too slow?
        
Matching runs in a background worker. If a job takes longer than about one second, usually because of nested quantifiers like (a+)+ on text that almost matches, the worker is stopped and a warning appears. The page stays responsive, so you can fix the pattern straight away.

      

      

        Is it really free?
        
Yes. It is open source under the MIT license, with no account, no limits and no ads. If it saves you a paid subscription, you can say thanks on Ko-fi.

      

      

        Does it work offline?
        
Yes. After your first visit the page is cached by a service worker, so it loads without a connection. You can also install it from your browser's menu as an app.

      

      

        Was this written by AI?
        
Yes. Regex Tester with Explanation was generated by Claude Code from a written specification inside an automated pipeline, with a test suite that runs in a real browser. The full source is on GitHub, so you can read every line before you trust it with your text.

      

      
    


    

      

        
Built by one person, given away for free

        
Regex Tester with Explanation is a free alternative to paid tools like regex101. If it earns a place in your bookmarks, a coffee keeps the updates coming.

        ☕ Support Or on Ko-fi