Regex Tester

Write a regex pattern, paste your test text, and watch every match highlight live as you type. Stop guessing whether your pattern works — see it work.

What is Regex Tester?

A Regex Tester allows you to test regular expressions against sample text in real-time. Essential for developers building text processing, validation, and search functionality in their applications.

Formula

Pattern + Flags → RegExp → Execute against Test Text → Matches array

Common patterns:

- \d+ → one or more digits

- [a-zA-Z]+ → one or more letters

- ^…$ → anchors for start/end

- (…) → capture groups

How to Calculate

Enter your regex pattern (e.g., \d{3}-\d{4}).
Select flags: g (global), i (case-insensitive), m (multiline), s (dotall).
Type or paste test text in the text area.
View all matches highlighted with count.

Example

Pattern: ^[\w.-]+@[\w.-]+\.\w{2,}$ with test text: "Contact us at hello@example.com or support@test.org" matches both email addresses and displays them in the results list.

Key Benefits

Test regex patterns in real-time
See all matches highlighted
Support for common flags
Free no sign-up required

Common Mistakes to Avoid

Not escaping special characters (use \. instead of .)
Forgetting the g flag when expecting multiple matches
Using greedy quantifiers when lazy ones are needed
Overcomplicating patterns — simpler is often better

Pro Tips

Test with both matching and non-matching text
Use online regex references for complex patterns
Start simple and add complexity incrementally
Use named capture groups for readability

Key Terms Explained

Pattern: Search expression
Flags: Options modifying search behavior
Match: Found occurrence of pattern
Capture group: Parenthesized portion of pattern

Common Use Cases

Validating email addresses, phone numbers, URLs
Extracting patterns from text (dates, prices, IDs)
Search and replace operations in text editors
Input validation in web forms

Frequently Asked Questions

What is a regular expression?

A regex is a sequence of characters defining a search pattern. It is used for pattern matching in text, such as finding email addresses, validating input, or extracting data from strings.

What regex engine does this use?

This tool uses JavaScript's built-in RegExp engine, which supports most standard regex features including groups, lookaheads, quantifiers, and character classes.

What are common regex flags?

g (global): Find all matches, not just first. i (case-insensitive): Ignore case. m (multiline): ^ and $ match line boundaries. s (dotall): . matches newlines.

Why is my regex not matching?

Common issues: missing the g flag for multiple matches, not escaping special characters (., *, +, ?, [, ], (, )), or incorrect quantifier usage.

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