Regex Builder
Build and test regular expressions visually.
Common Templates
Why use this builder?
Demystifying Regular Expressions
Overview
Regular expressions are a tiny domain-specific language for matching text patterns. They turn problems like 'find all email addresses' or 'extract date strings' into one-liners — but the cryptic syntax intimidates many developers. This builder helps you compose regex patterns visually, see live matches on test text, and learn the syntax piece-by-piece. It supports JavaScript's regex flavor (closest to most other modern engines).
How to Use (Step by Step)
- 1
Type your pattern in the regex box
Live highlighting shows every match in your test string as you type. No need to press anything — the matches update with each character.
- 2
Test against sample input
Paste real data into the test area. Tweak the pattern until matches look right; the hover tooltip explains what each part of the regex does.
- 3
Copy the pattern for your language
JavaScript, Python, Java, PHP, .NET — each has small dialect differences. The export menu adapts your tested pattern to the language you need.
How It Works
Type a pattern in the regex field; type test text in the test area. As you type, the tool highlights every match in real time. Groups and named groups are color-coded. The tool generates explanation text for each part of your pattern ('\d+ matches one or more digits') and warns about common mistakes (greedy quantifiers, missing escapes, unintended character classes).
When to Use This
Validating form input (email format, phone numbers, postal codes). Extracting data from log files. Find-and-replace in code editors. Building URL routing patterns. Parsing user-entered text. Sanitizing HTML or SQL. Splitting CSV with quoted fields. Designing regex for use in another tool (sed, grep, your code).
Frequently Asked Questions
Most common issue: greedy quantifiers. '.*' matches as much as possible; use '.*?' for lazy matching. Also check for character class issues — '[a-z]' doesn't match uppercase; '[a-zA-Z]' or the 'i' flag does.
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Demystifying Regular Expressions
Overview
Regular expressions are a tiny domain-specific language for matching text patterns. They turn problems like 'find all email addresses' or 'extract date strings' into one-liners — but the cryptic syntax intimidates many developers. This builder helps you compose regex patterns visually, see live matches on test text, and learn the syntax piece-by-piece. It supports JavaScript's regex flavor (closest to most other modern engines).
How to Use (Step by Step)
- 1
Type your pattern in the regex box
Live highlighting shows every match in your test string as you type. No need to press anything — the matches update with each character.
- 2
Test against sample input
Paste real data into the test area. Tweak the pattern until matches look right; the hover tooltip explains what each part of the regex does.
- 3
Copy the pattern for your language
JavaScript, Python, Java, PHP, .NET — each has small dialect differences. The export menu adapts your tested pattern to the language you need.
How It Works
Type a pattern in the regex field; type test text in the test area. As you type, the tool highlights every match in real time. Groups and named groups are color-coded. The tool generates explanation text for each part of your pattern ('\d+ matches one or more digits') and warns about common mistakes (greedy quantifiers, missing escapes, unintended character classes).
When to Use This
Validating form input (email format, phone numbers, postal codes). Extracting data from log files. Find-and-replace in code editors. Building URL routing patterns. Parsing user-entered text. Sanitizing HTML or SQL. Splitting CSV with quoted fields. Designing regex for use in another tool (sed, grep, your code).
Frequently Asked Questions
Most common issue: greedy quantifiers. '.*' matches as much as possible; use '.*?' for lazy matching. Also check for character class issues — '[a-z]' doesn't match uppercase; '[a-zA-Z]' or the 'i' flag does.