Regex Tester – Test Regular Expressions Online
Test and debug regular expressions in real-time. Our free regex tester shows matches highlighted, explains your pattern, and supports JavaScript, Python, and PCRE flavors—all in your browser.
What Is a Regex Tester?
A regex (regular expression) tester lets you build and test patterns against sample text. See what matches, debug issues, and refine your expressions before using them in code—saving time and preventing bugs.
Features
| Feature | Description |
|---|---|
| Real-Time Matching | See matches as you type |
| Match Highlighting | View all matches in context |
| Group Extraction | See captured groups |
| Multiple Flavors | JavaScript, Python, PCRE |
| Flag Options | Global, case-insensitive, multiline |
| Error Messages | Helpful syntax error feedback |
How to Use This Tool
Step 1: Enter Your Pattern
Type your regex pattern in the Pattern field.
Step 2: Paste Test Text
Enter the text you want to test against.
Step 3: Select Options
Choose flags: global (g), case-insensitive (i), multiline (m).
Step 4: Review Matches
See all matches highlighted in your test text.
Common Regex Patterns
| Pattern | Matches | Use Case |
|---|---|---|
\d+ | Numbers | Find digits |
[A-Za-z]+ | Words | Find letters |
\b\w+@\w+\.\w+\b | Emails | Email validation |
https?://\S+ | URLs | Find links |
\d{3}-\d{3}-\d{4} | Phone (US) | Phone numbers |
| `^\s+ | \s+$` | Whitespace |
Regex Syntax Reference
Anchors
| Pattern | Meaning |
|---|---|
^ | Start of line/string |
$ | End of line/string |
\b | Word boundary |
\B | Not word boundary |
Character Classes
| Pattern | Meaning |
|---|---|
[abc] | a, b, or c |
[^abc] | Not a, b, or c |
[a-z] | Any lowercase letter |
. | Any character (except newline) |
\d | Digit [0-9] |
\D | Non-digit |
\w | Word char [a-zA-Z0-9_] |
\W | Non-word char |
\s | Whitespace |
\S | Non-whitespace |
Quantifiers
| Pattern | Meaning |
|---|---|
* | 0 or more |
+ | 1 or more |
? | 0 or 1 |
{3} | Exactly 3 |
{3,} | 3 or more |
{3,5} | 3 to 5 |
Groups & Capturing
| Pattern | Meaning |
|---|---|
(abc) | Capture group |
(?:abc) | Non-capturing group |
(?<name>abc) | Named group |
\1 | Backreference to group 1 |
Regex Flags
| Flag | Name | Effect |
|---|---|---|
g | Global | Find all matches |
i | Case-insensitive | Ignore case |
m | Multiline | ^/$ match line starts/ends |
s | Dotall | . matches newlines |
u | Unicode | Full Unicode support |
Common Use Cases
Email Validation
^[\w.-]+@[\w.-]+\.\w+$
Matches: [email protected]
Phone Numbers
\(?(\d{3})\)?[-.\s]?(\d{3})[-.\s]?(\d{4})
Matches: (555) 123-4567, 555.123.4567
Date Formats
\d{1,2}[/-]\d{1,2}[/-]\d{2,4}
Matches: 12/25/2024, 1-1-24
IP Addresses
\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b
Matches: 192.168.1.1
Frequently Asked Questions
Why doesn't my regex match?
Common causes:
- Missing global flag (
g) for multiple matches - Unescaped special characters (
.,*,?) - Anchors (
^/$) preventing partial matches - Case sensitivity without
iflag
What's the difference in regex flavors?
Different programming languages have slightly different regex engines. JavaScript lacks certain features (lookbehind in older versions), while PCRE (Perl) supports more advanced features.
How do I match actual special characters?
Escape them with backslash: \. matches literal period, \\ matches backslash.
What are greedy vs. lazy quantifiers?
- Greedy (
*,+): Match as much as possible - Lazy (
*?,+?): Match as little as possible
Can I test replacement patterns?
Yes! Our tool supports testing replacement strings with captured groups ($1, $2, etc.).
Pro Tips
- Start simple — Build patterns incrementally
- Use non-capturing groups —
(?:)when you don't need captures - Be specific —
\dis better than.when matching numbers - Test edge cases — Try empty strings, special chars, Unicode
- Use named groups — Makes complex patterns readable
Common Mistakes
| Mistake | Problem | Fix |
|---|---|---|
email.com | Matches emailXcom | Use email\.com |
\d* | Matches empty strings | Use \d+ |
.* | Too greedy | Use .*? |
| No anchors | Partial matches | Add ^ and $ |
Related Tools
Explore more developer utilities:
- Find & Replace — Search and replace
- Text Compare — Diff comparison
- JSON Validator — Validate JSON
- Base64 Encoder — Encode/decode
- URL Encoder — URL encoding
Test your regular expressions above with real-time matching and syntax highlighting. Essential for developers working with pattern matching.