Regex Builder
Build common regular expressions step by step — then copy & test them on your data.
Pattern builder
Leave empty for “any length”.
Paste this into your code, or open it in the Regex Tester tool for deeper debugging.
Quick test
Matches are highlighted below.
What is a Regex Builder?
A regex builder helps developers construct regular expressions step by step without having to memorize the full syntax. Instead of writing a pattern from scratch, you can select rules such as “must contain digits”, “must start with a letter” or “must not contain spaces” and the tool generates the corresponding regular expression for you.
Why use a regex builder?
- Avoiding syntax errors when writing complex expressions
- Quickly generating patterns for validation rules
- Learning regex by seeing the pattern update in real time
- Sharing patterns with QA and backend engineers
- Standardizing input validation across an application
Common patterns you can build
- Email validation
- Phone number formats
- Usernames and login fields
- Transaction IDs and reference numbers
- Hex colors or UUIDs
- Alphanumeric token formats
Example: building a simple email regex
Steps:
- Allow alphanumeric characters before
@ - Require exactly one
@symbol - Allow a domain name with dots
- Require a TLD (2+ characters)
Generated expression:
^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$Unlike a pre-written snippet, a builder shows how each rule contributes to the final expression, making the learning curve much smoother for beginners.
Real-world usage scenarios
- Backend developers: input validation in API gateways or services
- Frontend developers: form validation for signup or checkout flows
- QA engineers: writing test patterns for automated validation tools
- Data engineers: extracting tokens or IDs from logs
- Security teams: sanitizing untrusted text or filtering payloads
Understanding flags
| g | Global — find all matches |
| i | Ignore case |
| m | Multiline mode |
| s | Dot matches newline |
| u | Unicode support |
Is this builder secure?
Yes — all building, compilation and test matching happens entirely in your browser. Nothing is uploaded or logged to a server, which makes the tool safe for testing production-like patterns or log fragments during development.
Related tools
- Regex Tester — test your generated expressions against sample text
- JSON Formatter — validate structured data before pattern matching
- Base64 — decode logs or tokens before applying regex filters
- JWT Decoder — extract and inspect claims that follow known patterns
A regex builder is an essential tool for developers and QA engineers who need to validate user input or extract structured tokens from text. Building patterns interactively helps reduce errors, improve maintainability and speed up development workflows.