Regex Tester & Debugger

Visual Match Highlighting

See exactly what your regex matches with color-coded highlighting. Unlike regex101 which shows matches in a separate panel, we highlight matches directly in your test string for instant visual feedback.

• Color-coded match highlighting in test string
• Match table showing all matches with positions
• Capture group extraction with group numbers
• Named capture group support

Find & Replace Mode

Test find & replace operations with live preview. Use capture group references ($1, $2) in replacement text and see results instantly before applying changes to your code.

• Live replacement preview as you type
• Capture group references ($1, $2, $3...)
• Named group references ($<name>)
• Copy result with one click

Test Case Management

Save test cases to validate your regex against multiple strings. Mark each test as "should match" or "should not match" and run all tests at once to verify your pattern works correctly across all scenarios.

• Add unlimited test cases
• Pass/fail indicators for each test
• Run all tests with one click
• Perfect for TDD regex development

Built-in Cheatsheet

Quick reference sidebar with all regex tokens, quantifiers, anchors, and special characters. No need to Google regex syntax—everything you need is right there in the tool.

• Character classes (\\w, \\d, \\s)
• Quantifiers (*, +, ?, {n,m})
• Anchors (^, $, \\b)
• Lookaround assertions
• Groups and alternation

What is a regular expression (regex)?

A regular expression (regex or regexp) is a sequence of characters that defines a search pattern, mainly for use in pattern matching with strings. Regex is used for text searching, validation (email, phone numbers), find & replace operations, and data extraction. It's supported in most programming languages including JavaScript, Python, Java, Go, PHP, and more.

What do the regex flags mean?

Flags modify how the regex pattern behaves. g (Global) finds all matches instead of stopping after the first. i (Ignore Case) makes matching case-insensitive. m (Multiline) makes ^ and $ match line boundaries instead of just string start/end. s (Dot All) makes . match newline characters.u (Unicode) enables full unicode support. y (Sticky) matches only from the lastIndex position.

How do I use capture groups in regex?

Capture groups are parts of your regex wrapped in parentheses that extract specific portions of matches. For example, in (\d{3})[-.](\d{3})[-.](\d{4})for phone numbers, the three groups capture area code, prefix, and line number separately. In replacements, reference groups with $1, $2, etc. Named groups use(?<name>pattern) and are referenced with $<name>.

What's the difference between greedy and lazy quantifiers?

Greedy quantifiers (*, +, {n,m}) match as much text as possible. For example, <.+> on "<a>link</a>" matches the entire string. Lazy quantifiers (*?, +?, {n,m}?) match as little as possible. <.+?> matches only "<a>" and "</a>" separately. Use lazy quantifiers when you want to match the shortest possible string.

How do I match special characters literally?

Special regex characters like . * + ? [ ] {} ( ) ^ $ | \\ have special meanings. To match them literally, escape them with a backslash. For example, to match a literal period, use\. instead of .To match "example.com" exactly, use example\.com. To match parentheses, use \( and \).

Why isn't my regex matching newlines?

By default, the dot (.) metacharacter doesn't match newline characters. To make . match newlines, enable the s (Dot All) flag. Alternatively, use [\s\S] or(.|\n) to explicitly match any character including newlines. For multiline matching where ^ and $ should match line boundaries (not just string start/end), enable the m (Multiline) flag.