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Free RegEx Tester & Builder Online
Free RegEx Tester & Builder Online is a free online tool by US AI. Test patterns live. It runs completely in your browser — no signup, no download, works on mobile and desktop.
📖 How to use
- Type a pattern, set flags or pick a preset, then test it live against your text. Matches are highlighted.
- Open the tool with the button above — it loads instantly.
- Your work stays on your device; nothing is uploaded anywhere.
✨ Why use this tool?
US AI's free regex tester & builder online is fast, private and 100% free forever. Bookmark this page and share it with anyone who needs it.
❓ Frequently asked questions
How do I test a regular expression?
Type your pattern, pick flags like g, i, or m (or start from a preset), then test it live against your text — every match is highlighted instantly.
Which regex syntax does the tester use?
It uses the JavaScript RegExp engine — the same syntax used in web development, Node.js, and most modern programming languages.
Can I build regex patterns on my phone?
Yes. The tester works in any mobile or desktop browser with no signup and no app to install.