🔍 Regex Tester

Free Online Regex Tester & Regular Expression Validator

Whether you are debugging a production bug at 2 AM or learning regex syntax for the first time, a reliable regex tester saves you hours of trial and error. EzyToolbox's free regular expression tester lets you paste any pattern, enter your test string, toggle flags, and instantly see every match highlighted — no sign-up, no install, no nonsense.

This guide explains how the tool works, covers how to test regex in the most popular languages, answers the most common "why is my regex not working?" questions, and gives you a quick-reference cheat sheet — all in one place.

What Is a Regex Tester?

A regex tester (also called a regex checker or regex validator) is an online tool that evaluates a regular expression pattern against a body of text and shows you exactly which parts match — in real time. Instead of writing test code locally, running it, reading console output, and iterating, you can iterate visually in seconds.

Regular expressions are sequences of characters that define a search pattern. They are used everywhere: form validation, log parsing, data extraction, find-and-replace operations in code editors, search filters in analytics platforms, and even router configuration. Because the syntax can be tricky, a dedicated regex match tester is an essential bookmark for every developer, data analyst, and DevOps engineer.

Our tool supports the three most common flags used in web-based regex testing: Case Insensitive (i), Multiline (m), and Singleline / Dotall (s). It also surfaces capture groups so you can see exactly what each group matches — a feature missing from many basic regex tools online.

How to Test a Regular Expression — Step by Step

1. Enter your pattern in the "Regular Expression Pattern" field. Do not include the surrounding slashes — just the pattern itself (e.g. \d{3}-\d{3}-\d{4}).
2. Choose your flags. Toggle Ignore Case if you want case-insensitive matching, Multiline if ^ and $ should match line boundaries, or Singleline if . should match newlines.
3. Paste your test string. This is the text you want to search within. You can use the "Load Sample" button for a quick demo.
4. See results instantly. Matches are highlighted as you type. Capture groups, match count, and character offsets are displayed below the test area.
5. Iterate. Tweak the pattern, re-run, and refine until it works perfectly — then copy it into your code.

How to Test Regex in Popular Programming Languages

Every language implements regular expressions slightly differently. Building your pattern here first — then copying it into your language of choice — prevents those frustrating "it works online but not in my code" moments.

🐍 Python Regex Tester

Python uses the built-in re module. The most common reason a Python regex fails is forgetting to use a raw string (r"..."), which causes backslashes to be interpreted by Python before the regex engine sees them.

import re

pattern = r"\d{3}-\d{3}-\d{4}"
text    = "Call us at 800-555-1234 or 212-867-5309"

matches = re.findall(pattern, text)
print(matches)  # ['800-555-1234', '212-867-5309']

# With capture groups
m = re.search(r"(\d{3})-(\d{3})-(\d{4})", text)
if m:
    print(m.group(1), m.group(2), m.group(3))
  

Use re.IGNORECASE, re.MULTILINE, and re.DOTALL as flags — they map exactly to the toggles in this tool.

🌐 JavaScript / JS Regex Tester

JavaScript regex lives in the language core — no imports needed. The JS regex tester above uses the same V8 engine that powers Node.js and Chrome, so patterns you build here work directly in your JavaScript code.

const pattern = /(\d{3})-(\d{3})-(\d{4})/g;
const text    = "Call 800-555-1234 or 212-867-5309";

let match;
while ((match = pattern.exec(text)) !== null) {
  console.log(`Full: ${match[0]}, Area: ${match[1]}`);
}

// Replace example
const masked = text.replace(/\d{3}-\d{3}-\d{4}/g, "XXX-XXX-XXXX");
console.log(masked);
  

The global flag (g) is implicit when using this tool — all matches are found, not just the first.

☕ Java Regex Tester

Java's java.util.regex package is PCRE-compatible for most common patterns. Double-escape backslashes in Java string literals: \d becomes "\\d".

import java.util.regex.*;

Pattern p = Pattern.compile("(\\d{3})-(\\d{3})-(\\d{4})");
Matcher m = p.matcher("Call 800-555-1234 today");
while (m.find()) {
    System.out.println("Match: " + m.group(0));
    System.out.println("Area code: " + m.group(1));
}
  

🔷 C# / .NET Regex Tester

The .NET regex tester (C#) uses System.Text.RegularExpressions. .NET has some unique features like named capture groups with (?<name>...) syntax and balancing groups.

using System.Text.RegularExpressions;

string pattern = @"(?<area>\d{3})-(?<exchange>\d{3})-(?<number>\d{4})";
string text    = "Call 800-555-1234";

Match m = Regex.Match(text, pattern);
if (m.Success) {
    Console.WriteLine(m.Groups["area"].Value);   // 800
    Console.WriteLine(m.Groups["number"].Value); // 1234
}
  

🐹 Golang Regex Tester

Go uses the regexp package, which is based on RE2 syntax — not PCRE. This means lookaheads and lookbehinds are not supported. If your pattern uses those, it will not compile in Go even if it works in the browser.

import (
    "fmt"
    "regexp"
)

re := regexp.MustCompile(`(\d{3})-(\d{3})-(\d{4})`)
matches := re.FindAllString("Call 800-555-1234", -1)
fmt.Println(matches) // [800-555-1234]
  

⚙️ PCRE Regex Tester (Perl Compatible Regular Expressions)

PCRE is the gold standard for advanced regex features: lookahead, lookbehind, atomic groups, possessive quantifiers, and named backreferences. PHP, Perl, Apache, Nginx, and many other tools use PCRE. Our tester uses a JavaScript engine that supports the most common PCRE features. If you need full PCRE2 support (e.g. for PHP's preg_match), test the core logic here and validate edge cases in a PCRE-specific environment.

🖥️ Bash Regex Tester

Bash uses POSIX Extended Regular Expressions (ERE) with the [[ =~ ]] operator or PCRE with grep -P. Note that \d is not valid in POSIX ERE — use [0-9] instead.

# POSIX ERE in bash
phone="800-555-1234"
if [[ $phone =~ ^[0-9]{3}-[0-9]{3}-[0-9]{4}$ ]]; then
    echo "Valid phone number"
fi

# PCRE via grep
echo "Call 800-555-1234" | grep -oP '\d{3}-\d{3}-\d{4}'
  

Google Analytics Regex Tester

Marketers and analysts use regex in Google Analytics 4 (GA4) and Google Search Console to filter traffic, segment audiences, and create custom reports. GA4 uses RE2-style regex (similar to Go), so lookaheads are not available there.

Common Google Analytics regex use cases include:

• Exclude internal traffic: ^192\.168\.|^10\.
• Group similar pages: ^/blog/ to capture all blog URLs
• Filter by campaign source: google|bing|duckduckgo
• Match specific query parameters: [?&]utm_medium=email

Build and validate your analytics filters here, then paste them directly into your GA4 property settings.

Regex Tester with Capture Groups

Capture groups are one of the most powerful regex features. They let you extract specific portions of a match — not just confirm that the match exists. Wrap part of your pattern in parentheses ( ) to create a group.

Our tool shows each capture group value individually below the match count — making it easy to verify data extraction logic before writing a single line of production code.

You can also use named capture groups ((?<name>...)) for more readable patterns, especially useful in Python, .NET, and modern JavaScript.

Regex Tester Multiple Lines (Multiline Mode)

By default, ^ matches the start of the entire string and $ matches the end. Enable the Multiline (m) flag to make them match the start and end of each individual line instead — essential when testing patterns against multi-line log files, CSV data, or any text with newlines.

Regex Cheat Sheet — Quick Reference

Copy these patterns directly into the tester above to see how they work:

Ready-to-Use Regex Patterns for Common Tasks

Click "Load Sample" in the tool above to see these in action:

Frequently Asked Questions

Pro Tips for Writing Better Regular Expressions

• Be specific, not greedy. Use character classes ([a-z]) over wildcards (.) wherever possible to prevent over-matching.
• Anchor when you mean it. If a pattern should match the whole string, use ^...$. Without anchors, a password pattern like [A-Z]\d will match anywhere inside the string.
• Use non-capturing groups for grouping without capturing. (?:http|https) is faster than (http|https) when you don't need the group value.
• Test edge cases. After your happy-path test works, try empty strings, very long strings, strings with special characters, and strings that almost match.
• Comment complex patterns. In Python, use re.VERBOSE to add inline comments and whitespace to long patterns for maintainability.
• Watch for ReDoS. Patterns with nested quantifiers like (a+)+ can cause catastrophic backtracking on malicious input. Always test with long, near-matching strings before deploying to production.