What do regex flags like g, i, m, and s mean?

"g" (global) finds all matches instead of just the first. "i" (case-insensitive) ignores letter case. "m" (multiline) makes ^ and $ match line boundaries within the text. "s" (dotAll) makes "." match newline characters as well.

Why is my regex not matching anything?

Common causes include unescaped special characters (like . or *), case sensitivity (try the "i" flag), anchors (^ or $) that do not align with your text, or a missing "g" flag when you expect to see multiple matches listed. Double-check that your pattern does not include the surrounding slashes — enter only the expression itself.

Do I need to wrap my pattern in forward slashes?

No. Type only the expression (e.g. [a-z]+), not the /pattern/flags literal form used in JavaScript source code. The tool displays the slashes and active flags separately for clarity.

Is it safe to paste sensitive text into this regex tester?

Yes. All matching runs entirely in your browser using client-side JavaScript. Your pattern and test text are never sent to a server. As a general precaution, avoid pasting production secrets or personal data into any online tool.

What regex flavor does this tool use?

This tool uses JavaScript's native RegExp engine, which follows ECMAScript regular expression syntax. Most common patterns work the same across languages, but advanced features like lookbehind or named capture groups depend on your browser's JavaScript version.

Why does my pattern show a syntax error?

A syntax error means the expression is not valid JavaScript regex — often caused by an unclosed bracket or parenthesis, an invalid quantifier, or a misplaced backslash. The error message points to the problem so you can correct the pattern.

Regex Tester - Test Regular Expressions Online

Overview

Regex Tester is a free tool on ToolifHub for building and debugging regular expressions against sample text in real time. Type a pattern, toggle flags (g, i, m, s), and paste test text to see every match highlighted instantly in context. A match-details panel lists each result with its character index and any capture groups, while invalid patterns surface a clear syntax error message so you can fix the expression before shipping it. One-click example buttons load ready-made patterns for email addresses, URLs, Indian phone numbers, hex colors, and digit extraction — useful when you're learning regex or validating a pattern quickly. Everything runs locally in your browser using JavaScript's native RegExp engine, so your test strings never leave your device.

About Regex Tester

Build and test regular expressions with real-time match highlighting, support for all standard flags (g, i, m, s), and a library of common pattern examples for email, URL, phone number, hex color, and digit extraction. See every match highlighted in context, review match index and capture groups, and catch invalid patterns instantly with clear syntax error messages — all without leaving your browser.

Key Features

Live match highlighting in the test text as you type

Toggle standard regex flags: g (global), i (case-insensitive), m (multiline), s (dotAll)

One-click example patterns for email, URL, phone (India), hex color, and digits

Match details panel showing matched text, index position, and capture groups

Instant syntax error feedback for invalid regular expressions

100% free with no sign-up — all testing happens locally in your browser

Benefits

Debug a regex pattern in seconds instead of writing a throwaway script

Visually confirm which parts of a string match before using the pattern in production code

Understand how flags change matching behavior by toggling them and watching results update live

Learn common regex patterns from built-in examples you can load and modify

Keep sensitive log excerpts, user input, or API responses private since nothing is sent to a server

How to Use Regex Tester

Enter your regular expression in the Pattern field (without surrounding slashes)

Toggle the g, i, m, and s flags to match your intended behavior

Paste or type sample text in the Test Text area

Review highlighted matches in the output panel and check the match count

Open Match Details to see each match, its index, and any capture groups

Load a Common Example to start from a proven pattern, then adjust it for your use case

Use Cases

Backend Developers

Validate input-validation patterns for emails, URLs, or IDs before adding them to server-side code.

Frontend Developers

Test form-validation regex against real user input samples without opening DevTools or a REPL.

QA & Testers

Confirm that a search-and-replace or log-parsing pattern matches the expected strings in sample data.

Data Engineers

Prototype extraction patterns for cleaning or parsing semi-structured text before writing a pipeline.

Students & Learners

Experiment with regex syntax and flags using built-in examples to see how patterns behave on real text.

Regex Tester

Overview

About Regex Tester

Key Features

Benefits

How to Use Regex Tester

Use Cases

Backend Developers

Frontend Developers

QA & Testers

Data Engineers

Students & Learners

Frequently Asked Questions

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