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Free Tab Toolsnothing uploaded

Runs in your browser · Last updated 4 September 2026

Regex Tester

Test a JavaScript regular expression against a string in the browser. Matches and capture groups stay on this device.

Matches

2

  • 0: Hello
  • 26: Python

How to use this tool

  1. Enter a pattern and flags.
  2. Paste the test string.
  3. Read match offsets and capture groups.

Worked example

The default \b[A-Z][a-z]+\b should highlight Hello, JavaScript, and Python in the sample sentence.

Frequently asked questions

Which engine?
JavaScript RegExp in this tab. Python, PCRE, and Java differ on lookbehind and possessive quantifiers.
Uploaded?
No. The haystack never leaves the browser.
Flags?
g i m s u y. g is added automatically so every match is listed.
How many matches?
The first 50 are shown. A runaway empty match stops at 500.
Is this a replacer?
No. Test and inspect groups. Rewrite in your editor.