Mastering regular expressions can feel like learning a superpower for text manipulation, but writing and debugging them can be tricky. Our free Online Regex Tester simplifies the process by providing instant, live highlighting of all matches in your test string. See exactly what your pattern is matching as you type, and get it right the first time.

Live Regex Tester

Regular Expression

Test String

Matches

How to Use Our Regex Tester

Testing your regular expressions is an interactive, real-time process:

Enter your regular expression pattern in the first input field (between the slashes).
Enter any flags (like `g` for global or `i` for case-insensitive) in the small flags box.
Type or paste the text you want to test into the "Test String" area.
As you type, all matching parts of the string will be highlighted instantly.
The "Matches" box below will list all the individual matches found.

Example: Finding Email Addresses

To find all email addresses in a block of text, you could use the following pattern:

[\w\.-]+@[\w\.-]+\.\w+

With the `g` (global) flag, our tool would highlight `john.doe@example.com` and `jane.doe@sub.example.org` in a test string, and list them both in the matches box.

What is a Regular Expression (Regex)?

A Regular Expression (often shortened to "regex" or "regexp") is a special sequence of characters that defines a search pattern. It's like a super-powered version of the "Find" feature in a text editor. Instead of finding a literal word, you can search for abstract patterns, making it an incredibly powerful tool for developers, data scientists, and system administrators.

With regex, you can:

Validate that user input matches a specific format (like an email address, phone number, or zip code).
Find and replace specific pieces of text within a large document or code file.
Extract structured data from unstructured text (like pulling all URLs from a block of HTML).
Split strings into an array based on a complex delimiter.

This tool uses JavaScript's built-in regex engine, which is a common and powerful implementation used in millions of websites and applications.

Quick Regex Cheatsheet

Common Metacharacters:

. - Matches any single character except newline.
\d - Matches any digit (0-9).
\w - Matches any word character (alphanumeric + underscore).
\s - Matches any whitespace character (space, tab, newline).
\b - Matches a word boundary.

Quantifiers:

* - Matches 0 or more times.
+ - Matches 1 or more times.
? - Matches 0 or 1 time (makes the preceding token optional).
{n} - Matches exactly n times.
{n,} - Matches n or more times.
{n,m} - Matches between n and m times.

Groups and Ranges:

[...] - Character set. Matches any single character inside the brackets (e.g., [aeiou]).
(...) - Capturing group. Groups multiple tokens together.
(a|b) - Matches either 'a' or 'b'.

Common Flags:

g - Global. Finds all matches rather than stopping after the first.
i - Case-insensitive.
m - Multi-line. Allows start (^) and end ($) anchors to match the start/end of lines, not just the whole string.

Frequently Asked Questions (FAQ)

Q1: Is my data safe to paste into this tool?

Yes, 100%. This is a client-side tool, meaning all regex testing and highlighting happens locally in your web browser using JavaScript. Your text is never sent to our servers, ensuring it remains completely private.

Q2: What "flavor" of regex does this tool use?

This tool uses the JavaScript regex engine that is built into your web browser. While most regex flavors are very similar, there can be minor differences in syntax or feature support compared to other engines like PCRE (used in PHP), Python's `re` module, or .NET's regex engine.

Q3: What does the "g" flag do?

The `g` flag stands for "global." Without it, a regular expression will stop after finding the very first match in the string. With the `g` flag, the engine will continue searching through the entire string to find all possible matches. This is essential for tasks like "find and replace all."

Online Regex Tester with Live Highlighting & Cheatsheet