Regex Tester
Free regex tester — free online regular expression testing tool with live matching. Test regex patterns for free. No registration required. Free regex validator and debugger online.Test and debug regular expressions with live matching, syntax highlighting, and named group support. Works entirely in your browser — nothing is sent to any server.
About the Regex Tester
Regular expressions (regex) are a powerful mini-language for matching, searching, and transforming text. This free online regex tester lets you write a pattern and instantly see all matches highlighted in amber inside your test string. Named capture groups are shown in a dedicated column so you can quickly verify complex patterns. Everything runs locally in your browser — no data ever leaves your machine.
How to Use
- Type your regex pattern into the Pattern field between the two slashes.
- Toggle the g i m s flags as needed. The g flag is always active to find all matches.
- Use the Quick presets to load common patterns for Email, URL, IPv4, Date, or Phone.
- Paste or type text into the Test String area — results update live on every keystroke.
- Scroll down to the Matches table to inspect each match's index, value, and any named groups.
Frequently Asked Questions
What regex flavour does this tester use?
This tool uses JavaScript's built-in RegExp engine, which follows the ECMAScript specification. It supports character classes, quantifiers, lookaheads/lookbehinds, and named capture groups.
What does the "g" flag do?
The global (g) flag tells the engine to find all matches rather than stopping after the first one. This tester always uses the g flag internally so the match count and table are always complete.
How do named capture groups appear?
If your pattern includes named groups such as (?<year>\d{4}), the Named Groups column in the match table will show each group name paired with its captured value for every match.
Is my data kept private?
Yes. All regex evaluation happens entirely in your browser using native JavaScript. No pattern, test string, or result is ever sent to any server or stored anywhere outside your current browser tab.
Why does my regex throw an error?
A red error banner appears when the browser's RegExp constructor cannot parse your pattern. Common causes include unescaped special characters, mismatched parentheses, or unsupported syntax. The banner shows the exact error message to help you fix it quickly.