Easily test your regular expressions with this free online Regex Tester. Validate, highlight, and replace patterns in real time — built for developers, learners, and QA professionals.
Regex Tester (Light Mode)
What is the Regex Tester?
The Regex Tester is an online tool that helps you test, debug, and visualize regular expressions (regex). Regular expressions are powerful text-matching patterns used in programming languages, data validation, and search systems to find or replace specific text patterns. With this free tool, you can quickly input your regex pattern, test text, and see all matched results instantly.
Why Do You Need a Regex Tester?
Regular expressions can be complex and tricky to debug. A Regex Tester lets you instantly see what your pattern matches — helping you avoid syntax errors, infinite loops, and incorrect captures. It saves time and effort for developers, testers, data scientists, and students learning pattern matching.
Some Facts About Regular Expressions
✔️ Regex is supported in almost all major programming languages including JavaScript, Python, PHP, Java, and C#.
✔️ They are used in search engines, data validation, log parsing, and web scraping.
✔️ A well-optimized regex can process large text files efficiently.
✔️ Regex is case-sensitive by default but can be made case-insensitive using the i flag.
Real-Life Examples of Regex Use
1️⃣ Validate an email: ^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$
2️⃣ Find all dates in YYYY-MM-DD format: \d{4}-\d{2}-\d{2}
3️⃣ Match all hashtags: (?<=\s|^)#(\w+)
4️⃣ Replace all numbers in a sentence with “X”: \d+
How to Use the Regex Tester Online
1. Enter your pattern in the input box (e.g. \d+).
2. Select flags such as g for global or i for case-insensitive search.
3. Add your test text in the text area.
4. Click “Run” to see matches highlighted instantly.
5. Optionally, use the Replace Preview section to visualize text replacements.
Why Use This Regex Tester?
This tool offers a clean, modern, and responsive interface designed specifically for WordPress. It supports live highlighting, capture group breakdown, and replacement previews. You can also copy results or export your regex test as a JSON file. It works entirely on your browser—no data is uploaded or stored externally.
General Information & History
The concept of regular expressions dates back to the 1950s, when mathematician Stephen Kleene introduced them as a way to describe regular languages. Later, regex became part of Unix systems and evolved into modern implementations found in JavaScript, Python, and other programming languages.
Regex Formulas & Syntax Examples
✔️ Match digits: \d+
✔️ Match words: \w+
✔️ Match whitespace: \s+
✔️ Match start of line: ^
✔️ Match end of line: $
✔️ Capture groups: (...)
✔️ Non-capturing groups: (?:...)
✔️ Optional elements: ?
✔️ Repetitions: + (1 or more), * (0 or more)
Tips for Writing Effective Regex
✅ Start simple and test often.
✅ Use flags like g, i, and m to control matching behavior.
✅ Escape special characters like ., [, and ( when needed.
✅ Avoid overly complex patterns to prevent performance issues.
✅ Use online testers like this one to validate before deploying your regex into code.
FAQ – Regex Tester Online
What does this Regex Tester do?
It evaluates your regex pattern against input text, highlights matches, and shows captured groups in real time.
Can I use it for programming languages like Python or JavaScript?
Yes! The Regex Tester uses JavaScript regex syntax, which is similar to most modern languages.
Is this tool free?
Yes, it’s completely free and works directly in your browser with no login required.
Can I share my regex pattern?
Yes, you can copy your pattern or export the session as a JSON file for sharing.
Does it support multiline or case-insensitive patterns?
Yes, you can use flags like m for multiline and i for case-insensitive matching.
Disclaimer
This tool is provided for educational and testing purposes only. While it accurately simulates JavaScript’s regex engine, syntax may slightly differ in other languages. Always verify your regex in the actual environment where it will be used.