Regex Tester Online Free
Tests a regular expression in the browser. Enter a pattern, optional flags (g, i, m, s, u, y), and a test string, then read match text and index. Matching uses the browser RegExp constructor. This is not a replace-all tool and not a file-grep tool.
Regex tester online free
Flags
Allowed flags: g, i, m, s, u, y. Unknown flags and duplicates fail closed.Client-side only. Uses the browser RegExp constructor. This is not a replace-all tool and not a file-grep tool. The pattern, flags, and test string are not sent to a server.
How to use
- Enter a pattern such as foo+ (no surrounding slashes).
- Toggle flags g, i, m, s, u, or y, then paste a test string.
- Read matches as text (match text and index). Zero matches is an empty result, not an error. Nothing is sent to a server.
Results
Enter a regular expression to test.
Runs in your browser. Nothing is uploaded.
Frequently asked questions
How does this regex tester run matching?
It uses the browser RegExp constructor: new RegExp(pattern, flags). Matches are found with RegExp.prototype.exec. With the g flag it returns every match; without g it returns the first match or none. This is the same regular-expression engine as your browser or Node, not a separate dialect.
Which flags are allowed?
Only g, i, m, s, u, and y (any unique subset). g is global (all matches). i is case-insensitive. m is multiline ^ and $. s lets dot match newline. u is Unicode. y is sticky. Unknown flags such as d or x fail closed. Duplicate flags such as gg also fail closed.
What is the difference between an empty pattern and an empty test string?
An empty pattern fails closed. A whitespace-only pattern also fails closed. An empty test string is valid when the pattern is valid: you get zero matches and no error. The test string is not trimmed, so a leading space is part of the text.
Is this a replace-all or file-grep tool?
No. This page tests a pattern against one string and lists matches as text (match text and index). It does not replace, rewrite, or search across files. There is no replace field and no folder or grep-across-files mode.
Is my pattern sent to a server? Do I need an account?
No. Matching runs in your browser. The pattern, flags, and test string are not sent to a server. There is no signup, and Tallymill does not save what you type. Refreshing the page clears the form.
Is this an exploit helper?
No. This is a client-side regex tester for ordinary match checks. It is not an exploit helper, payload cookbook, or ReDoS recipe list. Invalid patterns fail closed. Match text is shown as text only.
Is there a size limit?
Yes. A pattern or test string larger than 100KB (100 × 1024 UTF-8 bytes) is rejected. Empty patterns fail closed. Empty test strings are allowed when the pattern is valid. Nothing is sent to a server either way.