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Regex Lab - Test Regular Expressions Online

Test and debug regular expressions against logs, JSON, and text with real-time pattern matching and ReDoS protection. Perfect for DevOps and SRE teams.

Regex pattern & test data
Write or paste a regex and test it against real logs.
Regex pattern
Supports JavaScript-style regular expressions. Use \d, \w, groups( ), and character classes [ ].
Flags
Global matching is enabled by default so that all occurrences are highlighted.
Test data
Paste real log lines from Nginx, Kubernetes, application logs or JSON payloads. For sensitive data, scrub secrets before pasting.
Sample generators
These presets only change the test data. Use the cheat sheet on the right to load matching patterns.
Matches, groups & breakdown
See highlights, capture groups and a best-effort explanation.
Enter a regular expression to see how many matches it finds.
Captured groups
Add capturing groups ( ... ) to your pattern to see them listed here.
Regex breakdown (beta)

This is a best-effort explanation of common regex tokens (anchors, groups, character classes, quantifiers). Complex expressions may be simplified. Always rely on official documentation for critical use-cases.

Type a pattern to see a high-level summary here.
  • Start typing… Token-by-token explanations will appear here as you edit the pattern.
Log regex cheat sheet (click to load)
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Why Use Regex Lab?
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Testing regular expressions can be challenging, especially when working with production logs. Our Regex Lab provides a safe, interactive environment to test and debug your patterns with real-time feedback and ReDoS (Regular Expression Denial of Service) protection.

Whether you’re parsing Nginx logs, Kubernetes events, JSON data, or custom formats, this tool helps you craft the perfect regex pattern before deploying to production.

How to Use Regex Lab?
  • Enter Your Pattern: Type your regex pattern in the input field at the top
  • Choose Flags: Enable global (g), case-insensitive (i), or multiline (m) matching
  • Add Test Data: Paste your log data, JSON, or text in the test area
  • See Results: View real-time matches, groups, and pattern breakdown
  • Load Samples: Click sample buttons to load common log formats

Features
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ReDoS Protection
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Our tool automatically detects potentially dangerous regex patterns that could cause catastrophic backtracking:

  • Nested quantifiers like (a+)+ or (a*)*
  • Alternation with quantifiers like (a+|b+)+
  • Backreferences with quantifiers
  • Excessive repetition ranges (>1000)

Real-Time Matching
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  • Instant feedback as you type
  • Match highlighting in your test data
  • Capture group visualization
  • Match count and summary

Pattern Library
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Quick access to common regex patterns for:

  • Email validation
  • IP addresses
  • URLs and domains
  • Dates and times
  • Log severity levels
  • And more…

Common Use Cases
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Nginx Log Parsing
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Extract IP addresses, status codes, response times, and URLs from Nginx access logs.

Kubernetes Events
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Parse pod names, namespaces, timestamps, and error messages from kubectl output.

JSON Data Extraction
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Extract specific fields from JSON logs and API responses.

Error Log Analysis
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Find and group errors by severity, component, or error code.

Best Practices
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  • Start Simple: Begin with a basic pattern and refine it iteratively
  • Test Edge Cases: Include unusual inputs to ensure your pattern is robust
  • Watch for Performance: Pay attention to ReDoS warnings
  • Use Anchors: Use ^ and $ to match entire lines when needed
  • Escape Special Characters: Remember to escape .[]{}()*+?|^$\ when matching literally
  • Use Non-Capturing Groups: Use (?:...) instead of (...) when you don’t need to capture

FAQ
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Is my data sent to a server?
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No. All regex matching happens entirely in your browser. No data is transmitted to any server.

What regex flavor is supported?
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JavaScript regex (ECMAScript). Most patterns are compatible with other flavors, but some advanced features may differ.

Why am I seeing a ReDoS warning?
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Your pattern may cause exponential backtracking on certain inputs, which could freeze the browser. Simplify your pattern or avoid nested quantifiers.

Can I save my patterns?
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Currently, patterns are not persisted. Consider bookmarking the page or copying patterns to your notes.

How do I match across multiple lines?
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Enable the multiline (m) flag to make ^ and $ match line beginnings/endings, or use [\s\S]*? to match any character including newlines.