Regex Tester

Test and debug regular expressions with real-time match highlighting

Regular expressions (regex) are sequences of characters that define search patterns. This tester helps developers validate regular expression matches with real-time text highlighting and sub-group captures.

How to use Regex Tester

  1. Enter Pattern. Input your regular expression pattern.
  2. Enter Test String. Type standard text to see match highlights.

Features

  • Offline Processing: Computes operations instantly in your local browser client.
  • One-Click Copy: Instantly copy inputs or outputs to your clipboard.
  • Precision Outputs: Processes inputs immediately to provide clean, error-free results.

Why use this tool

  • Visual Validation: Instantly see matches highlighted in yellow.
  • Flag Support: Supports global (g), case-insensitive (i), and multi-line (m) flags.

Frequently asked questions

How do I test a regular expression online?

Enter your pattern, type or paste a test string and every match is highlighted immediately with a running count. Use the global toggle to find all matches instead of only the first, and the case-insensitive toggle to ignore letter case.

Which regex flavor does this tester use?

It runs the JavaScript (ECMAScript) regular expression engine built into your browser. Syntax such as lookahead, named groups and lazy quantifiers works, but features from other flavors, like Python inline flags or PCRE recursion, may not, so results can differ from your language.

Why does my regex only find one match?

Without the global flag, a regex stops after the first match. Turn on Global Search (g) to highlight every match in the text. If you still see too few matches, check that the pattern is not anchored with ^ or $ and that case sensitivity is what you expect.

What does an Invalid regular expression error mean?

The pattern has a syntax problem in JavaScript, such as an unclosed bracket or parenthesis, a quantifier with nothing before it like *abc, or an unescaped special character. Escape literal characters like . ? + ( ) [ ] with a backslash.

What is the difference between greedy and lazy matching?

Greedy quantifiers like .* match as much as possible, while lazy ones like .*? match as little as possible. On the text <b>one</b><b>two</b>, the pattern <b>.*</b> matches the whole string, but <b>.*?</b> matches each tag pair separately.

How do I match a literal dot or other special character?

Put a backslash before it. A plain . matches any character, so use \. to match a real full stop. The same applies to * + ? ( ) [ ] { } | ^ $ and the backslash itself. Inside a character class such as [.] most of these are already literal.

Is my data shared when using the Regex Tester?

No. Toolskyt operates under a zero-server policy. All calculations, data formatting, and file exports are executed locally on your machine.

Do I need to sign up or pay to use the Regex Tester?

No, this tool is 100% free. There are no limits, sign-ups, subscriptions, or hidden charges required.

Is it safe to paste API tokens or private JSON data here?

Yes, absolutely. The tool executes 100% inside your local browser memory space. No inputs are sent to any servers.

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