Regex Tester — Test and Debug Regular Expressions Online for Free

Our free online Regex Tester lets you write, test, and debug regular expressions in real time. Paste any text, type your pattern, and see matches highlighted instantly — with full support for capture groups, named groups, and all standard JavaScript flags. Everything runs in your browser, so your data never leaves your device.

What Is a Regular Expression?

A regular expression (regex) is a sequence of characters that defines a search pattern. Developers use regex to find, validate, extract, and replace text in strings. Regex is built into virtually every programming language — JavaScript, Python, Java, PHP, Go, and more — making it one of the most universal tools in a programmer's toolkit.

Despite its power, regex syntax is notoriously difficult to read. A pattern like ^(?:\+?(\d{1,3}))?[-. (]*(\d{3})[-. )]*(\d{3})[-. ]*(\d{4}) is incomprehensible at first glance, yet it reliably matches international phone numbers. That is exactly why a visual regex tester matters: it shows you exactly what your pattern matches, where it matches, and why — in real time.

Without a tester, developers resort to trial and error, running code over and over to see if a pattern works. Our tool eliminates that cycle by giving you instant feedback as you type your pattern and test string.

How to Use This Regex Tester

Getting started takes just a few seconds:

1. Enter your regex pattern in the pattern input field at the top. The tool uses the standard /pattern/flags syntax — just type the pattern between the slashes.
2. Paste or type your test string in the text area. This is the text you want to match against.
3. Toggle flags using the buttons below the pattern. Available flags include Global (g), Case Insensitive (i), Multiline (m), DotAll (s), and Unicode (u).
4. Review highlighted matches — every match is visually highlighted in the test string with a yellow background.
5. Inspect capture groups — the Match Details panel shows each match's index, capture groups, and named groups.
6. Copy results — click the Copy button to copy all match information to your clipboard.

All of this happens instantly in your browser. No network requests, no server processing, no data stored anywhere.

Key Features

Feature	Benefit
Real-time matching	See results as you type — no submit button needed
Match highlighting	Every match is visually highlighted in the test string
Capture groups	View all captured groups with their index and value
Named groups	Supports (?<name>...) syntax with labeled output
Flag toggles	Switch g, i, m, s, and u flags with one click
Error feedback	Invalid patterns show a clear, descriptive error message
Zero data transfer	All processing happens locally in your browser

Unlike many regex testers that send your patterns and test strings to a remote server, our tool runs entirely in your browser using JavaScript's built-in RegExp engine. This makes it safe for testing patterns against sensitive data like log files, API responses, or user input.

Common Regex Patterns

Here are some frequently used patterns you can test right away:

Pattern	What It Matches
\d+	One or more digits
[a-zA-Z]+	One or more letters (no accents)
^https?://	Strings starting with http:// or https://
\b\w+@\w+\.\w+\b	Simple email addresses
#[0-9a-fA-F]{3,6}	Hex color codes like #ff0000
(\d{4})-(\d{2})-(\d{2})	Dates in YYYY-MM-DD format with capture groups
(?<protocol>https?)://(?<domain>[^/]+)	Named groups extracting protocol and domain

If you need to generate a QR code containing a URL you just validated, try our QR Code Generator. For encoding data to safely include in URLs, use the Base64 Encoder.

Real-World Use Cases

Form Input Validation

Every web form needs validation — email addresses, phone numbers, ZIP codes, passwords. Regex patterns define what valid input looks like. Use this tester to fine-tune your validation patterns before deploying them to production. A well-tested regex prevents bad data from entering your database.

Data Extraction and Scraping

When working with log files, API responses, or raw HTML, regex helps extract specific values like IP addresses, timestamps, or URLs. Paste your raw data into the test string, write your pattern, and instantly see if it captures exactly what you need.

Search and Replace Preview

Before running a bulk find-and-replace operation in your code editor, test the pattern here to make sure it matches the right text — and only the right text. This prevents accidental modifications to similar but unrelated strings.

Learning Regular Expressions

Regex syntax is dense and unforgiving. This tool makes it visual and interactive. Start with simple patterns like \d+ and gradually build complexity, seeing exactly what changes with each character you add.

Tips for Writing Better Regex

• Start simple and build up. Write a pattern that matches one case first, then add complexity for edge cases.
• Use \b for word boundaries. Without it, cat matches inside concatenate. With \bcat\b, it only matches the standalone word.
• Prefer named groups. (?<year>\d{4}) is far more readable than remembering that group 1 is the year.
• Use [\s\S] instead of . for multiline matching. Or simply enable the DotAll (s) flag to make . match newlines.
• Avoid catastrophic backtracking. Patterns with nested quantifiers like (a+)+ can freeze on certain inputs. Test with realistic data to catch performance issues early.
• Test edge cases. Empty strings, very long inputs, special characters, and Unicode — make sure your pattern handles them gracefully.
• Use character classes wisely. \d is shorter than [0-9], and \w is shorter than [a-zA-Z0-9_]. Prefer the shorthand.

Frequently Asked Questions

Is this Regex Tester free to use?

Yes. The tool is completely free, requires no account, and has no usage limits. Use it as often as you need.

Does the tool store my patterns or test strings?

No. All regex matching runs entirely in your browser using JavaScript's built-in RegExp engine. Your patterns and text are never sent to any server. It is safe to use with sensitive data.

Which regex flavor does this tool use?

This tester uses the JavaScript (ECMAScript) regex engine. Most patterns are compatible with PCRE (PHP), Python's re module, and Java's java.util.regex. However, some advanced features like lookbehind assertions and Unicode property escapes may behave differently across engines.

What regex flags are supported?

The tool supports five standard JavaScript flags: g (global — find all matches), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — . matches newlines), and u (unicode — enables full Unicode support).

Can I test patterns with capture groups?

Yes. The Match Details panel displays every capture group for each match, including both numbered groups and named groups using the (?<name>...) syntax.

Why does my pattern work on other testers but not here?

Different regex engines have different features and syntax. If you are coming from a PCRE or Python tester, some features like atomic groups, conditional patterns, or inline modifiers may not be supported in JavaScript's regex engine. Check the MDN RegExp documentation for JavaScript-specific behavior.