Regex Tester Online
Regex Tester Online: free, instant and private. The pattern is compiled by the browser’s own engine, so the result matches what JavaScript will do in your code.
How the Regex Tester Online works
The Regex Tester Online takes Regular expression, Flags (g, i, m...), Test text and returns the answer instantly — no button to hunt for, no page reload. The pattern is compiled by the browser’s own engine, so the result matches what JavaScript will do in your code. An invalid pattern returns the engine’s exact error message instead of failing silently.
Enter your own numbers to replace the example values; the result panel updates as you type. Everything runs in this single page, so nothing you enter leaves your device.
Formula used
pattern compiled with your flags, then matched against the test text
| Symbol | Meaning |
|---|---|
| pattern | the regular expression body, without slashes |
| flags | g, i, m, s, u or y |
| test text | the input to match against |
The pattern is compiled by the browser’s own engine, so the result matches what JavaScript will do in your code. An invalid pattern returns the engine’s exact error message instead of failing silently.
Inputs used: Regular expression, Flags (g, i, m...), Test text.
Worked example
Take the default example — regular expression of [a-z]+, flags (g, i, m...) of gi, test text of 2026-09-24:
- matchCount: 0
- matches:
Frequently asked questions
- What formula does the Regex Tester Online use?
- It uses pattern compiled with your flags, then matched against the test text, where pattern is the the regular expression body, without slashes; flags is the g, i, m, s, u or y; test text is the the input to match against.
- Is the Regex Tester Online free?
- Yes. There is no signup, no usage limit and no watermark — the checker runs entirely in your browser.
- How do I read the result?
- The pattern is compiled by the browser’s own engine, so the result matches what JavaScript will do in your code. An invalid pattern returns the engine’s exact error message instead of failing silently.
- Does the Regex Tester Online store or send my data?
- No. Every calculation happens locally in the page, so the numbers you type are never uploaded or logged.
- Does it work on a phone and offline?
- Yes — the page is a single lightweight file that adapts to any screen size. Once it has loaded it keeps working without a network connection.