# Regex Benchmark

Compare performance of different regex patterns, identify bottlenecks, and detect degenerate cases

> Canonical page: https://elysiatools.com/en/tools/regex-benchmark

- **Category:** Development

- **Keywords:** regex, benchmark, performance, testing, optimization, regexp, comparison

## Overview

## Regex Performance Benchmarking Tool

This tool helps you:
- **Compare multiple regex patterns** to find the fastest one
- **Identify performance bottlenecks** in your regular expressions
- **Detect degenerate cases** that cause catastrophic backtracking
- **Get optimization recommendations** for better performance

## Features
- Accurate timing with warmup phase for JIT optimization
- Statistical analysis (avg, min, max, median)
- Performance tier classification (fast/medium/slow/very-slow)
- Automatic detection of common anti-patterns
- Degenerate case testing for edge cases

## Usage
1. Enter multiple regex patterns (one per line)
2. Provide test input strings (one per line)
3. Set iterations and warmup runs
4. Choose regex flags (e.g., 'gi', 'm')
5. Run benchmark to compare performance

## Performance Tips
- Use non-capturing groups `(?:...)` instead of capturing groups
- Avoid nested quantifiers like `(.*)+`
- Use atomic groups `(?>...)` or possessive quantifiers to prevent backtracking
- Be specific with character classes instead of `.\*`
- Anchor patterns with `^` and `$` when possible

## Inputs

- **Regex Patterns** (textarea): Enter multiple regex patterns (one per line) Example: .* \[a-z\]+ \d{3}-\d{3}-\d{4}
- **Test Inputs** (textarea): Enter test strings (one per line) Example: hello world 123-456-7890 test@example.com
- **Regex Flags** (text): Flags to apply to all patterns (e.g., gi, m, i)
- **Iterations** (number): Number of iterations per test (1-10000)
- **Warmup Runs** (number): Warmup iterations for JIT optimization (0-1000)
- **Regex Engine** (select)
- **Include Degenerate Cases** (checkbox)

## When to use

- When selecting the fastest regex pattern for data validation or parsing tasks in code.
- When troubleshooting performance bottlenecks in applications that rely on regular expressions.
- When testing new regex patterns to ensure they do not exhibit degenerate behavior under load.

## How it works

- Input multiple regex patterns and corresponding test strings into the tool's interface.
- Configure parameters such as iteration count, warmup runs, and regex flags to simulate real-world conditions.
- Execute the benchmark to receive detailed performance metrics including average, min, max, and median times.
- Analyze results to identify performance tiers (fast/medium/slow/very-slow) and get optimization recommendations.

## Use cases

- Optimizing regex for log file parsing in a monitoring system to reduce processing time.
- Comparing validation patterns for user input in a web form to improve application responsiveness.
- Testing security-related regex for input sanitization to prevent ReDoS (Regular Expression Denial of Service) attacks.

## Frequently asked questions

### What regex engines are supported?

The tool supports JavaScript (V8) and simulated Python regex engines for benchmarking.

### How does the warmup phase improve accuracy?

Warmup runs allow JIT optimization in JavaScript, leading to more realistic and stable performance measurements.

### Can I test patterns with different flags like case-insensitive matching?

Yes, you can specify regex flags such as 'i' for case-insensitive or 'g' for global matching in the configuration.

### What are degenerate cases in regex?

Degenerate cases are patterns with nested quantifiers that cause exponential backtracking, leading to severe performance issues.

### How can I use the results to optimize my regex?

The tool provides performance classifications and tips, such as using non-capturing groups or atomic groups to prevent backtracking.

## Related tools

- [Java Regex Tester](https://elysiatools.com/en/tools/java-regex-tester): Test java.util.regex patterns online: (?…) named groups, possessive quantifiers and atomic groups, Pattern flags, ASCII vs UNICODE\_CHARACTER\_CLASS \\d semantics, and ready-to-paste Java code.
- [PCRE2 Regex Tester](https://elysiatools.com/en/tools/pcre-regex-tester): Test PCRE2 patterns online: every named-group syntax ((?P), (?), (\\u0027n\\u0027)), possessive quantifiers, atomic groups, \\A \\z \\h shorthands, plus pcre2grep and C API snippets.
- [Regex Cheat Sheet](https://elysiatools.com/en/tools/regex-cheat-sheet): A searchable, localized cheat sheet for regular expression syntax — character classes, anchors, quantifiers, groups & references, lookarounds, escape sequences, and flags — with a built-in quick tester
- [Image Difference](https://elysiatools.com/en/tools/image-difference): Calculate the difference between two images to identify changes or create comparison masks
- [API Breaking Changes Detector & Migration Planner](https://elysiatools.com/en/tools/api-breaking-changes-detector-migration-planner): Compare two OpenAPI 3.x schemas, identify breaking changes, grade client impact, and suggest migration or compatibility strategies
- [BGP Community Regex Tester and Looking-Glass Explainer](https://elysiatools.com/en/tools/bgp-community-string-regex-tester-and-looking-glass): Validate RFC 8294 BGP community regex patterns against a set of communities, match sample AS-paths, and generate Cisco/Juniper/FRR route-policy output.
- [Regex Linter](https://elysiatools.com/en/tools/regex-linter): Detect error-prone and risky regex patterns, check for catastrophic backtracking, unanchored patterns, and provide rewrite suggestions
- [CURB-65 vs PSI vs SMART-COP (Pneumonia Severity Comparison)](https://elysiatools.com/en/tools/curb-65-vs-pneumonia-severity): Compare three pneumonia severity scores side-by-side from one set of inputs to support concordance reading. CURB-65 (0-5: Confusion, Urea, RR, BP, age ≥65) — quick bedside triage; PSI/PORT (Fine 1997, 5 risk classes) — the most accurate mortality stratification, more complex; SMART-COP (0-10, 2 points each for SBP <90 and hypoxia, 1 point each for multilobar CXR, albumin <3.5, RR ≥25, tachycardia ≥125, confusion, pH <7.35) — predicts need for ICU respiratory/vasopressor support. Each score has a different focus: CURB-65 is fast; PSI is more precise; SMART-COP identifies who needs ICU. The tool reports each score's total/category/interpretation and an agreement analysis (whether all three point to outpatient/admission/ICU). When scores disagree, favor the more conservative disposition. Derived from Lim 2003, Fine 1997, Charles 2008. Not medical advice.

## Samples

- [Regex Pattern Alternatives](https://elysiatools.com/en/samples/regex-alternatives): Multiple ways to write the same regex pattern with different trade-offs in readability, performance, and accuracy
- [Regex Replace Samples](https://elysiatools.com/en/samples/regex-replace): Collection of common and useful regex replacement patterns for text transformation and data cleaning
- [Risky Regex Patterns](https://elysiatools.com/en/samples/risky-regex): Collection of regex patterns that demonstrate security vulnerabilities, performance issues, and common anti-patterns to avoid
- [Regex Named Capture Groups](https://elysiatools.com/en/samples/regex-named-groups): Collection of regex patterns using named capture groups for extracting structured data from text. Named groups make patterns more readable and maintainable by assigning meaningful names to captured portions.

## Related content

- [Regex Testing, Visualization, and Safety Workflow](https://elysiatools.com/en/hubs/regex-utility): Build reliable regular expressions by learning syntax, testing matches, visualizing structure, previewing replacements, benchmarking alternatives, and scanning for ReDoS risk.