CZF

CZF Tools

Privacy-first tools for web teams

Developer Tools

Regex Tester

Test regular expressions against sample text and inspect matches.

Pattern and flags inputs
Match list with positions
No signup or server processing required

Pattern setup

Use standard JavaScript regex patterns and flags.

Matches

Review values and match positions to understand the pattern.

team@example.com

Index: 0

support@czftools.com

Index: 30

Common use cases

  • Checking patterns during form validation work
  • Testing search-and-replace logic before coding it
  • Teaching teammates what a regex actually matches

FAQ

Which regex engine does this use?

It uses the browser's JavaScript regular expression engine, which matches many frontend use cases closely.

Can I test flags like global or case-insensitive?

Yes. You can enter standard JavaScript regex flags such as g, i, and m.

How it works

A browser-based regex playground for quickly checking patterns, flags, and match positions. The result is produced immediately so you can review it before copying or using it elsewhere.

Privacy

The tool is designed to process ordinary input in your browser. Avoid pasting passwords, private keys, access tokens, personal records, or other sensitive production data into any online utility.

Limitations

This utility handles the focused workflow described on this page. Check the result before production use, especially when an input depends on a vendor-specific format, security rule, or external standard.

Learn the essentials

Understanding Regex Tester

A regular expression describes a text pattern. Testing against representative input helps reveal incorrect matches, missing edge cases, and escaping problems before the pattern is used in an application.

Build patterns in small steps

Start with the smallest literal match, then add groups, repetition, boundaries, and alternatives one at a time. This makes failures easier to explain than beginning with one large expression.

Flags change the result

Case-insensitive, multiline, global, and dot-all modes can materially change what a pattern matches. Record the required flags with the expression instead of treating them as an afterthought.

Avoid unsafe assumptions

A regex that works on sample text may still behave poorly on unexpected or very large input. Authentication, HTML parsing, and complex validation often require a dedicated parser or library rather than one expression.

Related guide

Regex Groups, Captures, and Replacements

A practical guide to grouping regular expressions, reusing captured text, and avoiding common replacement mistakes.

Read the guide →