How to use Regex Tester
- Enter a JavaScript pattern without the surrounding slashes.
- Paste the sample text and choose the flags you need.
- The matches update as you change the pattern or the sample. Read the match positions and capture groups.
- If the time limit stops a pattern, shorten the sample or revise the repetition.
Example: Regex Tester
Find email-like text in two lines.
You add
Pattern: (\w+)@(\w+)\.(\w+); text: [email protected] and [email protected]; Global on.
You get
Two matches with line and column positions and three capture groups per match.
Supported inputs and limits
Uses the browser's JavaScript regular-expression flavor, not PCRE or Python syntax. The pattern is capped at 200 characters, sample text at 100,000 characters and displayed matches at 2,000. A background worker is stopped after 1.5 seconds; timing depends on the visitor's device. Email-like matches are not email-address validation.
Where your input is processed
This tool processes your input in this browser. Your text and files are not uploaded to UseFreeTools. Check this tool's limits for anything it may save on your device.
Questions about Regex Tester
Why did a pattern work in another regex tool but fail here?
Regex flavors differ. This page uses JavaScript syntax and the selected JavaScript flags; PCRE-specific features may not compile.
Why did the pattern stop before showing matches?
Some patterns take too long on particular text. The background worker is stopped after the time limit so the page stays usable.
What does Global change?
Global asks for successive matches. With it off, the page reports the first match only.
Are match positions byte offsets?
No. Positions follow JavaScript text indexing, which counts UTF-16 code units. A character outside the basic multilingual plane may use two units.