Regex Tester Online

What is a regular expression (regex)?

A regular expression, or regex, is a sequence of characters that defines a search pattern. It is commonly used to search, match, validate, extract, and replace text in programming languages, databases, text editors, and command-line tools.

What is a Regex Tester?

A Regex Tester is a tool that allows you to write regular expressions and instantly see which parts of your input text match. It helps developers debug, validate, and improve regex patterns before using them in applications.

Which regex flavor does this tool use?

This tool uses the JavaScript (ECMAScript) regular expression engine, which is supported by all modern web browsers and Node.js.

Which regex flags are supported?

You can enable the following JavaScript regex flags: g (Global matching), i (Case-insensitive matching), m (Multiline mode), and s (DotAll mode). These flags can be enabled individually or combined depending on your matching requirements.

Are capture groups displayed?

Yes. Both numbered capture groups and named capture groups are displayed for every successful match, making it easier to understand how your regular expression captures data.

Does this tool support lookaheads and lookbehinds?

Yes. JavaScript regular expressions support positive and negative lookaheads, and modern JavaScript environments also support lookbehinds where available.

What are character classes?

Character classes define sets of characters that can match a single position in text. Examples include \d for digits, \w for word characters, \s for whitespace, and custom ranges such as [A-Z].

What are quantifiers?

Quantifiers specify how many times a character or group may appear. Common examples include *, +, ?, and {n,m}, allowing patterns to match repeated text efficiently.

What are anchors in regex?

Anchors match positions rather than characters. For example, ^ matches the beginning of a line, while $ matches the end of a line.

Can I validate email addresses and URLs?

Yes. This tool is commonly used to test patterns for validating email addresses, URLs, phone numbers, usernames, passwords, dates, postal codes, and many other text formats.

Why isn't my regex matching?

A pattern may fail because of incorrect syntax, missing flags, greedy matching, character escaping, or differences between regex flavors. Testing your pattern with sample input can help identify the issue.

Does this tool modify my text?

No. The Regex Tester only analyzes and highlights matches. Your original text remains unchanged.

Does this tool support Unicode characters?

Yes. JavaScript regular expressions support Unicode, allowing you to test patterns against multilingual text, accented characters, emoji, and many international character sets.

Is my data uploaded to a server?

No. All regular expression matching happens locally in your browser. Your text, regex patterns, and test data are never uploaded or stored on any server.

Can I use this tool offline?

Yes. Once the webpage has loaded, all regex matching and highlighting run locally in your browser without requiring an internet connection.

Who can benefit from this Regex Tester?

This tool is useful for web developers, backend developers, QA engineers, DevOps engineers, data analysts, cybersecurity professionals, students, educators, and anyone who works with text processing or regular expressions.

Which programming languages use regular expressions?

Regular expressions are supported by JavaScript, TypeScript, Python, PHP, Java, C#, Go, Ruby, Rust, Kotlin, Swift, Perl, and many other programming languages. While syntax varies slightly between regex engines, the core concepts remain similar across platforms.

Why should I test regex before using it?

Testing regular expressions helps prevent incorrect matches, reduces bugs, improves validation accuracy, simplifies debugging, and ensures your pattern behaves correctly before deploying it in production code.