Regex Tester
Test regular expressions against sample text with live matches and capture groups.
/…/gWhy use our Regex Tester?
Live Match Highlighting
Type a pattern and see matches update instantly — no save button, no server round trip.
JavaScript RegExp Engine
Test patterns exactly as they run in browsers and Node.js with native RegExp semantics.
Capture Group Visibility
Inspect numbered groups and named captures so extraction logic is clear before you ship code.
What is a Regex Tester?
A regex tester is a developer tool that lets you write regular expressions against sample text and see which substrings match. Regular expressions are compact patterns for searching, validating, and extracting structured data from strings — used in form validation, log parsing, URL routing, and data cleanup.
Our free online regex tester uses the JavaScript RegExp engine in your browser. Toggle flags like global (g), ignore case (i), multiline (m), and dotAll (s), then review live highlights, match counts, and capture groups. Everything runs locally so test data never leaves your device.
Regex Tester Capabilities
- Pattern input:Write and edit regular expressions with immediate feedback on syntax errors.
- Test string:Paste logs, HTML, JSON, emails, or any sample text to match against.
- Flags g/i/m/s:Enable global, ignore case, multiline, and dotAll modes like production RegExp.
- Live matches:See highlighted matches and a match list update as you type.
- Capture groups:View numbered and named groups for each match to design extractors.
- Browser-only:100% client-side — patterns and sample text are never uploaded.
Common Use Cases
Form Validation Rules
Prototype email, phone, and password patterns before adding them to frontend or API validators.
Log Parsing
Extract timestamps, request IDs, and error codes from server log excerpts.
URL & Path Routing
Test route patterns for Express, Next.js, or nginx location blocks.
Data Cleanup
Find duplicate whitespace, unwanted characters, or malformed tokens in CSV exports.
HTML & Markup Scraping
Iterate on patterns for tags, attributes, and inline content before writing parsers.
Interview & Learning
Practice lookahead, groups, and quantifiers with instant visual feedback.
How to Use the Regex Tester
Enter Your Pattern
Type a regular expression in the pattern field. Slashes are optional — the tool treats input as a RegExp body.
Set RegExp Flags
Toggle g, i, m, and s flags to mirror how the pattern will run in your JavaScript code.
Paste Test Text
Add sample strings, logs, or documents into the test input area.
Review Matches & Groups
Scan highlighted matches and expand capture groups to confirm extraction logic.
Benefits of Using a Regex Tester
Faster Pattern Iteration
Avoid edit-compile-run loops when tuning complex expressions.
Accurate JS Semantics
Results match browser and Node RegExp behavior, not a different regex dialect.
Clear Group Debugging
See exactly which substring lands in each capture before writing replace logic.
Private Test Data
Keep production logs and customer PII on your machine during pattern development.
No Install Required
Test regex in the tab you already have open — no IDE plugin or CLI setup.
Completely Free
Unlimited testing with no signup, rate limits, or paywall.
Regex Testing Tips
- •Start simple: Match a literal substring first, then add anchors, groups, and quantifiers incrementally.
- •Use the right flags: Multiline (^/$ per line) and dotAll (. matches newlines) change results dramatically — enable them when needed.
- •Prefer non-greedy quantifiers: Use *? and +? when parsing HTML or nested structures to avoid over-matching.
- •Name your groups: Named captures (?<name>...) make replacement strings and code easier to read.
- •Escape metacharacters: Dots, brackets, and parentheses are special — escape them when matching literals.
- •Test edge cases: Include empty strings, Unicode, and line breaks in sample text before shipping validators.
Start Testing Regex Patterns Now
Whether you are validating forms, parsing logs, or extracting data from messy strings, our free regex tester gives you live JavaScript RegExp matches with full flag and capture group support. Iterate on patterns in seconds without leaving your browser.
Scroll up, enter your pattern and test text, and see matches highlight instantly. No registration required, completely free, and your data stays 100% private on your device.
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Frequently Asked Questions
Which regex flavor does this tester use?
It uses the JavaScript RegExp engine built into your browser — the same semantics as Node.js and modern frontend code.
What do the g, i, m, and s flags mean?
g finds all matches (not just the first), i ignores case, m makes ^ and $ match line boundaries, and s lets . match newline characters.
Are my patterns and test text uploaded?
No. All matching runs entirely in your browser. Nothing is sent to a server.
Can I see capture groups?
Yes. Each match shows numbered and named capture groups so you can verify extraction before using the pattern in code.
Why does my pattern work here but fail in another tool?
Different languages use different regex engines (PCRE, .NET, Python). This tool reflects JavaScript only — always test in the engine you deploy.
Does the global flag affect the results list?
Yes. Without g, only the first match is returned. With g, the tool finds every non-overlapping match in the test string.
Is this regex tester free?
Yes. Free unlimited use with no registration or downloads.
Can I test multiline strings?
Yes. Paste multiline text and enable the m and/or s flags when your pattern needs line-based anchors or dot-all behavior.