What is a regex tester?

A regex tester is an online tool that lets you write a regular expression pattern, paste test text, and instantly see which parts of the text match your pattern.

Which regex engine does this tester use?

This tester uses the JavaScript ECMAScript RegExp engine, the same engine used in modern browsers and Node.js.

How do I test a regular expression online?

Enter the pattern, paste a test string, choose the flags you need, and review the live match preview, match count, positions, and capture groups.

Can I use capture groups in Replace mode?

Yes. Use $1, $2, and later group references in the replacement field to reuse captured values in the replacement output.

What do the regex flags g, i, m, s, and u do?

g finds all matches, i ignores case, m treats each line separately for ^ and $, s lets dot match newlines, and u enables Unicode-aware matching.

What is the difference between a match and a global match?

Without g, JavaScript stops after the first match. With g enabled, it scans the full string and returns every occurrence.

Why is my regex pattern not matching anything?

Common causes include missing flags, anchors that are too strict, unescaped special characters, case sensitivity, or a pattern that is valid but does not fit the test text.

Is my pattern or text uploaded?

No. Matching and replacement run locally in your browser. Your pattern, test string, and replacement text are not uploaded.

Regex Tester Online Test, debug, validate, extract, and replace JavaScript regular expressions

Choose a common pattern for email, phone, URL, dates, or numbers, or write your own regex to inspect matches, capture groups, positions, and replacement output directly in the browser.

Pattern Finder

/pattern/g 0 matches

Pattern

Flags

//g

Test String

Quick Examples

PrivateProcessed LocallyNo Uploads

All processing happens in your browser No data is stored or sent to any server

What Is a Regular Expression?

A regular expression is a compact search pattern used to match, validate, extract, or replace text. This tester uses the JavaScript RegExp engine, so results match browser and Node.js behavior.

How To Use This Regex Tester

Use this as a regex validator, regex debugger, regex pattern tester, and regex replace tester for JavaScript-style regular expressions.

Enter a regular expression pattern in the Pattern field without the surrounding slashes.
Paste the text, log line, API response, or form value you want to test in the Test String field.
Toggle flags such as g for all matches or i for case-insensitive matching.
Review highlighted matches, positions, lengths, and capture groups in the preview and details panels.
Switch to Replace mode to preview replacement output with $1, $2, and other capture references.

Regex Flags Explained

g

Global. Finds every match instead of stopping after the first result.

i

Case-insensitive. Matches uppercase and lowercase letters without treating them as different.

m

Multiline. Makes ^ and $ match the start and end of each line.

s

DotAll. Lets the dot character match newline characters too.

u

Unicode. Enables stricter Unicode-aware matching and property escapes in supported browsers.

Common Regex Patterns

Email address

[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}

URL

https?:\/\/[^\s]+

Phone number

$?\d{3}$?[\s.\-]?\d{3}[\s.\-]?\d{4}

Numbers only

\d+

Date in YYYY-MM-DD format

\d{4}-\d{2}-\d{2}

Replace with capture groups

Use a pattern like (\d{4})-(\d{2})-(\d{2}) and replace with $3/$2/$1 to turn 2026-07-02 into 02/07/2026.

Why Regex Patterns Fail

The pattern is invalid

Unclosed parentheses, broken character classes, and invalid quantifiers can stop a regex from compiling. The tester shows the browser error below the Pattern field.

Special characters are not escaped

Characters such as ., +, *, ?, and \ have special meaning. Escape them when you want a literal match.

Only one match appears

Enable the g flag when you want every occurrence. Without it, JavaScript returns only the first match.

Case or line boundaries do not match

Use i for case-insensitive text and m when ^ or $ should work across multiple lines.

Greedy quantifiers match too much

Patterns such as .+ match as much as possible. Add ? after the quantifier, such as .+?, when you need a lazy match.

JavaScript Regex Compatibility

This online regex tester uses JavaScript regular expressions, also called ECMAScript RegExp. That makes it a good fit for frontend validation, browser scripts, Node.js services, and JavaScript test cases.

Regex syntax is not identical across every language. PCRE, Python, PHP, Ruby, Java, and .NET can support features or edge behavior that differs from JavaScript. When building for another engine, use this tester for quick pattern feedback and confirm advanced features in your target runtime.

Developer And Tester Use Cases

Find common patterns faster: load email, phone number, URL, number, alphanumeric, date, or password examples from Pattern Finder.
Extract values from text: provide a pattern and paste logs, API output, form data, or copied text to list every matching value.
Validate before coding: test form rules for emails, IDs, dates, slugs, and custom inputs before adding them to frontend or backend validation.
Debug match problems: check flags, escaping, anchors, case sensitivity, greedy matching, and invalid regex syntax.
Inspect capture groups: verify date parts, IDs, domains, file extensions, or log fields before using them in parser logic.
Preview replacements: test redaction, date reformatting, cleanup, masking, and capture-group replacements before applying them to real data.
Prepare documentation and tests: copy tested patterns and matched outputs into README files, API docs, QA tickets, or unit tests.