How do I test a regular expression online?

Type your pattern in the Regex field, toggle any flags you need, then type or paste text in the test area. Matches are highlighted instantly as you type. Click on any match card to see its position, length, and capture groups.

What regex flags are supported?

This regex tester supports all standard JavaScript flags: g (global — find all matches), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — dot matches newlines), and u (unicode — enable full Unicode support).

Is my text and regex private?

Yes, completely. All regex matching, replacing, and testing runs in your browser using JavaScript. Nothing is sent to any server. Your patterns and test strings never leave your device.

What regex presets are included?

The tool includes 20+ ready-to-use presets for common patterns: email addresses, URLs, phone numbers, IPv4/IPv6, hex colors, dates, credit card numbers, postal codes, HTML tags, JWT tokens, UUID, and more. Click any preset to load it instantly.

Regex Tester Online Free 2026 — Real-time Validator, Groups & Replace | YouKip

Developer Tool · Free & Private

Regex Tester
& Validator

Real-time · Highlighting · Groups · Replace · 20+ Presets

✓ 100% Free ✓ Match Highlighting ✓ Capture Groups

test.string — editor

matches0

chars0

lines0

groups0

replace.engine — backreferences

Replace with

$& = full match · $1 $2 = numbered groups · $<name> = named group

matches.results

⌨ Enter a pattern above and type test text

exec time—

first at—

history.patterns

No history yet — test a pattern to save it

cheatsheet.reference

Characters

.Any char except newline

\dDigit [0-9]

\wWord char [a-zA-Z0-9_]

\sWhitespace

\bWord boundary

Quantifiers

*0 or more (greedy)

+1 or more

?0 or 1 (optional)

{n,m}Between n and m

*?Lazy (non-greedy)

Groups

(abc)Capture group

(?:abc)Non-capture group

(?<n>abc)Named group

(?=abc)Lookahead

(?!abc)Negative lookahead

Anchors & Sets

^Start of string/line

$End of string/line

[abc]Character set

[^abc]Negated set

a|bAlternation (a or b)

Everything a regex engine needs

Real-time Matching

Every keystroke triggers an instant match. Zero delay, zero button clicks. See results as you type.

Match Highlighting

Toggle visual highlighting to color-code every match in your test text. Up to 5 distinct match colors.

Capture Groups

Numbered and named capture groups are extracted and displayed for every match. Full group inspection.

Replace Engine

Full JavaScript replace with backreferences. Use $&, $1, $2, or $<name> to build powerful transforms.

20+ Presets

Email, URL, phone, IP, hex color, date, UUID, JWT, credit card — click any preset to load it instantly.

100% Private

All matching runs in your browser. Your patterns and text are never sent anywhere. Zero tracking.

Keyboard Shortcuts

Ctrl+HToggle highlight

Ctrl+EnterApply replace

Ctrl+Shift+CCopy all matches

Ctrl+Shift+XClear test text

Ctrl+Shift+RReset replace

EscClear regex input

FAQ

What is a regex tester?

A regex tester lets you write and test regular expressions against sample text in real-time. It shows which parts match, highlights capture groups, displays positions and counts, and lets you test replace operations. This tool uses JavaScript's native regex engine.

What does the g flag do in regex?

The g (global) flag finds all matches in the string, not just the first one. Without it, the regex engine stops after the first match. Most practical use cases — counting occurrences, replacing all instances — require the g flag enabled.

How do I use capture groups in regex?

Wrap parts of your pattern in parentheses: (\d{4})-(\d{2})-(\d{2}) for a date. Group 1 captures the year, 2 the month, 3 the day. Use named groups with (?<year>\d{4}) for clarity. In the replace engine, reference them with $1, $2, or $<year>.

How does the replace engine work?

Enter your replacement string and click Apply. Use $& for the entire match, $1 $2 etc. for numbered groups, and $<name> for named groups. For example with pattern (\w+) and replacement [$1], every word becomes [word]. Click Reset to restore the original text.

Is my data private?

Completely. All processing runs in your browser using JavaScript. Your regex patterns and test strings never leave your device. No server, no analytics on your input, no logging. This tool also works fully offline after the first page load.

Free Regex Tester Online — JavaScript Regular Expression Engine 2026

The YouKip Regex Tester is the most complete free regex tool for JavaScript developers in 2026. Whether you're building form validation, parsing log files, processing API responses, or cleaning data, this tool gives you instant visual feedback for every pattern you write.

Features include real-time match highlighting, named and numbered capture group extraction, a full replace engine with backreferences, flag toggles (g, i, m, s, u), 20+ preset patterns, persistent history, and an interactive regex cheatsheet.

Everything runs in your browser — zero tracking, zero server, 100% private. Free forever, no account needed.