Live JavaScript Regex Tester

Edit a regular expression and inspect its matches in sample text as you type. Test syntax and performance in your target runtime.

This guide and page information are in English. Some controls inside the interactive tool currently appear in Turkish.

This tool processes its main input in your browser and does not send it to an external API. Fonts and interface assets may load from external providers.

YULATOOLS · TOOL GUIDE

Live JavaScript Regex Tester

The live regex tester refreshes match highlighting as you edit a pattern or sample text. That quick feedback can help when drafting straightforward validation or extraction expressions.

The preview follows the browser's JavaScript regular expression behavior. Other languages and runtimes may differ; test against your real input limits and target engine before relying on a pattern in production.

When is it useful?

  • Drafting a pattern to find a username format in sample text.
  • Checking whether a date fragment can be matched in a log line.

How to use it

  1. Enter a pattern and select the flags the expression needs.
  2. Add sample text and inspect the highlighted matches.
  3. Try empty, long and unexpected inputs, then check the same pattern in its intended programming language.

Example

Input: \bcat\b with the sample text: 'a cat sat'

Output: Only the standalone word 'cat' is highlighted

Who is it for?

  • Developers drafting JavaScript regular expressions
  • People inspecting text extraction patterns
  • Teams checking a regex against representative samples

Privacy and limitations

Pattern matching runs in the browser and the sample text is not sent to an API by this tool. Avoid pasting sensitive data; complex patterns and long input can use significant browser time.

JavaScript Regular Expressions: Patterns, Flags and Testing

Frequently asked questions

Why do the highlighted matches change?

The preview recalculates as the pattern, flags or sample text changes. Check options such as case-insensitive, global and multiline matching.

Which regular expression engine does it use?

It uses the browser's JavaScript regular expression engine. Syntax and behavior are not guaranteed to match other languages.

Does this tool prove that a regex is safe?

No. Do not treat a preview as a security review. Test patterns against realistic production limits and avoid sharing sensitive sample data.

Can I paste a very long sample?

The browser's available resources set the practical limit, and some complex expressions may become slow on long input. Start with a small sample and expand carefully.