Regex Tester
Test regular expressions with live match highlighting and group breakdown
Common Patterns
[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}URL
https?://[^\s]+Phone
\(?\d{3}\)?[\s.-]?\d{3}[\s.-]?\d{4}Hex Color
#[0-9A-Fa-f]{6}IP Address
\b(?:\d{1,3}\.){3}\d{1,3}\bWhat is Regex Tester?
Regular expressions (regex) are one of the most powerful — and most frustrating — tools in a developer's toolkit. A single pattern can validate an email address, extract all URLs from a document, parse log timestamps, or sanitize user input. But regex syntax is notoriously difficult to read and write correctly, especially with lookaheads, backreferences, and non-greedy quantifiers. Our free Regex Tester gives you an interactive environment to write, test, and debug regular expressions against real text with live feedback. As you type your pattern, every match is highlighted in the test string instantly — no need to click a button or run code. The tool displays all matches in a list, shows captured groups by index and name, and clearly indicates when a pattern has no matches. It supports all JavaScript regex flags: global (g), case-insensitive (i), multiline (m), dotAll (s), and unicode (u). Whether you are writing input validation for a web form, building a text parser, crafting a find-and-replace pattern for a code editor, or learning regex syntax for the first time, this tool makes the process visual and immediate.
How to Use Regex Tester
- 1
Enter Your Pattern
Type your regular expression in the pattern field — without the surrounding slashes. Select any flags you need (g for all matches, i for case-insensitive, m for multiline). The tool validates your pattern syntax immediately.
- 2
Paste Your Test String
Enter the text you want to test against — an email address, a log file excerpt, a URL, a block of HTML, or any string. Matches are highlighted in real time as you type in either field.
- 3
Inspect Matches and Groups
See every match highlighted in the text. The matches panel lists each match with its position index and the value of any captured groups (parentheses), so you can verify your pattern captures exactly what you intended.
Use Cases
Validating Form Input Patterns
Before writing a regex for email validation, phone number formatting, or password rules in production code, test it here against a set of valid and invalid examples. Catch edge cases — like an email with a plus sign or a phone number with country code — before they reach your users.
Parsing Log Files and Structured Text
Server logs, access logs, and application logs follow consistent patterns that regex can parse far more efficiently than manual string splitting. Build and test your log parsing pattern here against sample lines, then copy it directly into your log processing script, ELK pipeline configuration, or monitoring tool.
Writing Find-and-Replace Patterns for Code Editors
VS Code, Sublime Text, and JetBrains IDEs all support regex in their find-and-replace dialogs. When you need to rename variables across a codebase, reformat imports, or restructure JSX props, write and test the pattern here with real code samples before running a global replacement that could affect hundreds of files.
Features
Live Match Highlighting
Every match is highlighted in the test string in real time as you type, giving you immediate visual feedback without needing to run or submit anything.
Captured Group Breakdown
Displays each match with its captured groups listed by index (e.g., Group 1, Group 2) and by name for named capture groups (e.g., (?<year>\d{4})).
All JavaScript Regex Flags
Toggle global (g), case-insensitive (i), multiline (m), dotAll (s), and unicode (u) flags individually to see how they change the matching behaviour.
Syntax Error Detection
Invalid regex patterns are caught immediately with a clear error message, so you know whether your pattern is syntactically broken or just matching nothing.
Match Count and Position
Shows the total number of matches and the character index of each match in the test string — useful when writing parsers that need position information.
Frequently Asked Questions
This tool uses JavaScript's built-in RegExp engine, which follows the ECMAScript regex specification. JavaScript regex is broadly compatible with other modern flavours but has some differences: it does not support lookbehind in older environments (though modern browsers do), does not natively support atomic groups or possessive quantifiers, and uses a different syntax for named capture groups ((?<name>...)) compared to Python or .NET ((?P<name>...)).
Without the global flag, a regex stops after finding the first match. With the global (g) flag, it finds all non-overlapping matches in the test string from left to right. For most real-world use cases — extracting all URLs, validating that all tokens in a string match a pattern — you want the global flag enabled.
A capturing group is a part of your regex wrapped in parentheses, e.g., (\d{4}). The text matched inside the parentheses is captured and can be accessed separately from the full match. Named groups use (?<name>...) syntax. They are essential for extracting specific parts of a match — for example, capturing the year, month, and day separately from a date string like 2024-03-15.
Common reasons: (1) the pattern is case-sensitive and the text uses different capitalisation — add the i flag; (2) the anchors ^ and $ match start/end of the entire string but you have multiline text — add the m flag; (3) special characters like ., *, (, ) are not escaped with a backslash when you want to match them literally; (4) the quantifier is greedy and consuming more than you expect — try adding ? after * or + to make it non-greedy.
.* is a greedy quantifier — it matches as many characters as possible while still allowing the overall pattern to match. .*? is a non-greedy (lazy) quantifier — it matches as few characters as possible. For example, against the string <b>bold</b> and <i>italic</i>, the pattern <.*> greedy matches the entire string from first < to last >, while <.*?> matches each individual tag separately.
Need a Professional Website?
JAIDOO EMPIRE builds fast, SEO-optimised websites for businesses worldwide. All free tools are built and maintained by our team.
Start Your Project
