Add Pattern Blocks
Pattern Builder
Click blocks above to build your pattern
Drag blocks to reorder them
Generated Pattern
/<empty>/gFlags
Privacy Guaranteed
All regex building and testing happens entirely in your browser. No data is sent to any server.
About RegEx Builder
Build and test regular expressions visually with our free online regex builder. Features an intuitive block-based pattern creator where you can click to add characters, quantifiers, groups, anchors, and lookarounds. See your pattern explained in plain English as you build. Test your regex against sample text with real-time match highlighting, capture group extraction, and find-and-replace mode. Export your regex to JavaScript, Python, PHP, and more. Includes a comprehensive library of common patterns for emails, URLs, phone numbers, dates, and more. All processing happens locally in your browser - your data never leaves your device.
Understanding Regex Flags
gGlobal
Find all matches in the string, not just the first one. Essential for finding multiple occurrences.
iCase Insensitive
Match both uppercase and lowercase letters. "Hello" matches "hello", "HELLO", "HeLLo".
mMultiline
Makes ^ and $ match the start and end of each line, not just the entire string.
sDotAll
Makes the dot (.) match newline characters too. Useful for matching across lines.
uUnicode
Enable full Unicode support. Required for matching emoji and non-ASCII characters correctly.
ySticky
Match only from the lastIndex position. Useful for parsing and tokenizing.
Common Use Cases
- Form Validation: Validate email addresses, phone numbers, passwords, and other user input
- Data Extraction: Extract specific patterns from log files, documents, or API responses
- Search and Replace: Find and replace text patterns in code editors and documents
- URL Routing: Define route patterns in web frameworks
- Syntax Highlighting: Match code tokens for syntax highlighting in editors
Regex Tips
- Start simple: Build your pattern incrementally, testing each part
- Use non-greedy quantifiers: Add
?after*or+to match as few characters as possible - Escape special characters: Use
\before. * + ? ^ $ { } [ ] \ | ( ) - Use character classes:
\d,\w,\sare shorter than[0-9],[a-zA-Z0-9_],[ \t\n\r] - Use named groups:
(?<name>pattern)makes regex more readable and maintainable - Test edge cases: Always test empty strings, very long strings, and special characters
Frequently Asked Questions
How do I use the visual pattern builder?
Click on pattern blocks in the Build tab to add them to your regex. Each block represents a regex component like characters, quantifiers, groups, or anchors. You can reorder blocks by dragging them and configure each block's options.
What regex flags are supported?
We support all JavaScript regex flags: g (global - find all matches), i (case-insensitive), m (multiline - ^ and $ match line starts/ends), s (dotAll - . matches newlines), u (unicode - full Unicode support), and y (sticky - match from lastIndex).
What are capture groups?
Capture groups are portions of a regex pattern enclosed in parentheses (). They capture the matched text for later use. Named groups use (?<name>pattern) syntax and can be referenced by name instead of number.
How does the replace mode work?
Replace mode lets you test regex replacement operations. Use $1, $2, etc. to reference capture groups in your replacement string, or $<name> for named groups. $& inserts the entire match.
Is my data safe when using this tool?
Yes! All regex building and testing happens entirely in your browser using JavaScript. Your patterns and test strings are never sent to any server, ensuring complete privacy.
Can I export my regex to different programming languages?
Yes! Use the Export panel to copy your regex as a JavaScript literal, a string for new RegExp(), or code snippets for Python, PHP, and other languages.