Regex Tester
Test a regular expression against sample text online for free, with live match highlighting, capture groups, and flag support. Nothing sent to a server.
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Flags
Contact us at hello@example.com or support@example.org for help.
Your files are processed locally in your browser and are not uploaded to our servers.
How to use Regex Tester
- 1
Type or paste a regular expression pattern — no need to add the surrounding slashes.
- 2
Toggle flags like case-insensitive or multiline as needed.
- 3
Type or paste sample text — matches highlight instantly as you type.
- 4
Check the match details list below for each match's position and captured groups.
Common uses
- Building and debugging a regex before dropping it into code
- Checking whether a pattern matches real sample data, including edge cases
- Understanding what a regex found in a chunk of text, including capture groups
Supported formats and limitations
Accepts text, up to one file at a time.
- Uses your browser's native JavaScript regex engine — patterns rely on JavaScript regex syntax, which differs in some details from PCRE, Python, or other regex flavors.
- A pathological pattern with catastrophic backtracking can make matching slow or freeze this tab, the same way it would in any JavaScript environment — there's no execution timeout.
Frequently asked questions
No. Matching runs entirely in your browser using JavaScript's native RegExp — nothing is sent to a server.
No — just type the pattern itself. The slashes shown around the input are just a visual reminder of the flags applied.
Case insensitive (i), multiline (m), dot-matches-newline (s), and unicode (u). Matches are always found globally so every occurrence is shown, not just the first.
The pattern isn't valid JavaScript regex syntax — the error message shown is the browser's own explanation of what's wrong (e.g. an unterminated group or invalid flag combination).