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Regex Tester

Developer Tools

Test regular expressions with match highlighting

Quick Answer

Regex Tester: Test regular expressions with match highlighting. Regex Tester uses standard developer formulas to compute accurate results instantly.

Presets:

Pattern

//g
g=global i=ignoreCase m=multiline s=dotAll

Test string

Matches2
First index5
Flagsg
EngineJavaScript

Highlighted result

main 13812345678, backup 19987654321

Match list

#MatchIndexGroups
1138123456785—
21998765432125—

Syntax cheatsheet

TokenMeaning
\d \w \sdigit / word / whitespace
.any char except newline
* + ?0+ / 1+ / 0 or 1 times
{n,m}repeat n to m times
[abc] [^abc]set / negated set
^ $ \bstart / end / word boundary
( ) (?: )capture / non-capture group
a|balternation (or)

💡 Beware catastrophic backtracking with nested quantifiers like (a+)+ — it can freeze the page on crafted input. Prefer atomic, specific patterns.

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How to Use

  1. Paste or type content: drop code/text into the Regex Tester or fill the parameters.
  2. Choose mode/options: switch format, rules or processing as needed.
  3. Live output: results appear instantly — nothing is submitted, data stays in your browser.
  4. One-click copy: copy the output straight into your development environment.

Key Points

  • Regex Tester is a free online developer tool — open and use, no sign-up.
  • All calculations run locally in your browser; your data never leaves the device.
  • Key capability: Test regular expressions with match highlighting.
  • Results come with formulas and reference tables so you can verify every number.

Formula & How It Works

Regex Tester formula

Regex Tester uses standard developer formulas to compute accurate results instantly.

FAQ

How do I use the Regex Tester?
Open the page and fill in the input fields — results update automatically. Test regular expressions with match highlighting.
Are the results accurate?
Yes. Standard formulas and conversion factors are used and verified.
Is it free? Do I need to sign up?
Completely free. No registration, login or download required.
Does it work on mobile?
Yes. The responsive design works on phones, tablets and desktops.
Is my data saved?
No. Everything runs locally in your browser.

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Source & Updates

Based on RFC 4648, ECMA-262 and related specifications. Last updated: 2025-07

Last updated:

Formulas and content on this page are reviewed by the YiJianSuan team. For reference only — official sources prevail.

Maintained and periodically reviewed by the YiJianSuan editorial team — review process in ourEditorial Policy.

Cite this page: YiJianSuan. Regex Tester[EB/OL]. https://www.yijiansuan.com/en/c/dev/regex

Results provided by this tool are for reference only and do not constitute professional advice.