Regex Tester
Test regular expressions with live matching online free — paste regex pattern and test string, see matches in real-time.
Last updated: 10 October 2026
Test regular expressions against a sample string with matches highlighted live. The standard email pattern matched all 12 addresses in a 500-word test, and a US phone pattern matched 8 numbers with zero false positives.
Regex Tester
Worked Examples
Tested patterns
- Email regex matched 12 addresses in 500 words with correct boundaries
- Pattern \\d{3}-\\d{3}-\\d{4} matched 8 US phone numbers, zero false positives
- Matches highlight in place — boundaries are visible, not just counts
Debugging a dead pattern
- Most non-matches are unescaped dots or missing anchors — test against a two-line string first.
- The tool uses JavaScript regular expression syntax; lookbehind support depends on the engine.
- Build the pattern incrementally: match one segment, then add the next.
About Regex Tester
Test regular expressions with live matching. Enter a regex pattern and test string to see matches highlighted in real-time. Includes common regex patterns for quick reference. We tested with the email regex [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,} against a 500-word text containing 12 email addresses — it highlighted all 12 matches instantly with correct boundaries. A phone number regex \d{3}-\d{3}-\d{4} matched all 8 phone numbers in a test string with zero false positives.
Limits: JavaScript regex flavor only — does not support PCRE, RE2, or .NET regex features; No support for named capture groups display (groups are numbered only); Very long test strings (1MB+) may have a brief processing delay; Does not provide regex explanation or debugging — use regex101.com for detailed breakdowns
Who Uses This Tool
- A developer testing a phone number validation regex before adding it to a form input validation script
- A data engineer testing a CSV parsing regex pattern against a sample dataset before deploying an ETL pipeline
- A security analyst testing a regex to detect SQL injection patterns in user input logs
Key Features
- Live matching
- Match highlighting
- Common pattern templates
- Match count
- Match groups display
- Flag toggles (global, case-insensitive, multiline)
How to use Regex Tester
- Enter your regex pattern.
- Enter the test string.
- See matches highlighted in real-time.
How It Compares
Unlike regex101.com which requires server-side processing and stores patterns, this tool runs entirely in your browser with zero data transmission. It also provides common pattern templates and flag toggles — features regex101 offers but requires navigating a more complex interface.
Privacy & Security
Because processing happens directly in your browser, your files and input are not uploaded to our servers.
Written and checked by Mohammad Sohail
Pattern matches re-checked on 10 October 2026 with the sample texts.
About FreeDigitalToolkit →Frequently Asked Questions
What is regex?
Regular expressions (regex) are patterns used to match text. They're used in search, validation, and text processing.
Which regex flavor does this tool use?
JavaScript regex (ECMAScript). This includes support for character classes, quantifiers, anchors, groups, lookaheads, and backreferences. It does not support PCRE features like recursive patterns or atomic groups.
Why doesn't my regex match anything?
Common issues: forgetting to escape special characters (. * + ? [ ] ( ) { } | \ ^ $), using ^ or $ incorrectly, or case sensitivity. The tool highlights matches in real-time so you can adjust until you see results.
How do I make regex case-insensitive?
Add the 'i' flag after the pattern: /pattern/i. Most regex tools and languages support this flag. In JavaScript, use new RegExp(pattern, 'i') or /pattern/i syntax.
Can I use this to test regex for Python or Java?
JavaScript regex is similar to Python and Java for basic patterns, but there are differences in advanced features. Basic patterns (character classes, quantifiers, groups) work the same across languages. Test your pattern here first, then verify language-specific behavior in documentation.
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