Regex Tester & Generator

What is a Regex Tester?

A regex tester is a tool that lets you write a regular expression pattern and instantly see which parts of a test string it matches. It highlights all matches, shows capture group values, and updates in real time as you type, eliminating the need to run code just to verify a pattern.

How to Use the Regex Tester

1. Type or paste your regular expression into the Pattern field (without the surrounding slashes).
2. Toggle the flags you need — g for global (find all matches), i for case-insensitive, m for multiline, or s for dotall mode.
3. Enter the text you want to test against in the Test String area.
4. Matches appear automatically in the results panel, along with their index positions and any capture group values.
5. Use the Common Patterns library to load pre-built patterns for emails, URLs, phone numbers, and more.
6. Copy the finalized pattern with the copy button for use in your code.

Common Use Cases

• Form validation: Build and test patterns for email addresses, phone numbers, or postal codes before embedding them in your app.
• Log parsing: Extract timestamps, error codes, or IP addresses from large log files.
• Search and replace: Prototype complex find-and-replace operations before running them in an IDE or script.
• Data scraping: Validate patterns used to extract structured data from HTML or plain text.
• URL routing: Test route patterns for web frameworks that use regex-based routing.
• Learning regex: Experiment with syntax and flags interactively to understand how regular expressions work.

Why Use an Online Regex Tester?

Writing regular expressions without live feedback is slow and frustrating. Running a script to check each tweak adds friction to what should be a quick iteration loop. An online regex tester shows you exactly which characters matched, which capture groups were populated, and where the match starts and ends — all without leaving your browser. The built-in pattern library also gives beginners a solid starting point for the most common matching tasks.

Frequently Asked Questions

What regex flavour does this tester use?

This tool uses JavaScript's built-in RegExp engine, which follows the ECMAScript standard. It supports most common syntax — character classes, quantifiers, anchors, lookaheads, and named capture groups — but does not support lookbehinds in older browsers or POSIX-specific syntax.

What does the global (g) flag do?

Without the global flag, the regex stops after the first match. With g enabled, it finds every non-overlapping match in the entire test string and returns them all, which is the most common behaviour needed for search, replace, and extraction tasks.

How do I match a literal dot or bracket?

Special regex characters like ., [, ], (, ), *, +, and ? must be escaped with a backslash to be treated as literals. For example, to match a period use \., and to match a literal opening parenthesis use \(.

Related Tools

Explore more free developer tools: JSON Formatter — format and validate JSON. Diff Checker — compare two blocks of text to find differences. URL Encoder — encode special characters for use in URLs.