Regex Tester
Test your regular expressions against a string with real-time match highlighting and detailed results. Fast, private, and runs entirely in your browser.
\dDigit\wWord character\sWhitespace[a-z]Lowercase letter[A-Z]Uppercase letter^patternStart of stringpattern$End of string*0 or more+1 or more?0 or 1.Any character(group)Capture group(?:group)Non-capturing group\/Escape characterWhat is a Regular Expression?
A regular expression (often shortened to regex or regexp) is a sequence of characters that specifies a search pattern in text. It's a powerful tool used in programming and text editing to find, replace, and validate strings. Regex patterns can range from simple character matches to complex patterns involving various operators, quantifiers, and groupings.
When to Use a Regex Tester
A regex tester is an essential utility for developers, data analysts, and anyone working with text data. It provides a sandbox to build, debug, and refine regular expressions before implementing them in code. Use a tester to validate form inputs (like emails or phone numbers), parse log files, scrape data from websites, or perform complex find-and-replace operations in your editor. This tool helps you see exactly what your pattern is matching in real-time, saving you from frustrating trial-and-error in your application.
What is a Regex Tester?
A regex tester is an interactive tool that lets you write, test, and debug regular expressions against sample text in real time. Regular expressions, often shortened to regex or regexp, are powerful pattern-matching sequences used across virtually every programming language and text processing tool. They can match, search, extract, and replace text based on complex patterns, but their compact syntax can be difficult to read and write correctly. Our regex tester on caseconverter.co.uk provides instant visual feedback as you type your pattern, highlighting all matches in your test string and showing capture groups, match positions, and flags. All processing happens in your browser using JavaScript's built-in RegExp engine, so your data stays private and results appear without any server round-trip.
How to Use the Regex Tester on caseconverter.co.uk
Using the regex tester on caseconverter.co.uk is intuitive. Type your regular expression pattern into the pattern input field at the top. Enter or paste your test string into the text area below. The tool immediately highlights all matches in your test string as you type. You can toggle regex flags like global (g), case-insensitive (i), and multiline (m) using the flag buttons. The results panel shows each match with its position, length, and any captured groups. You can also use the replace field to test substitution patterns and see the replacement result in real time.
When to Use a Regex Tester
The regex tester is essential for developers working with text processing, data validation, or search functionality. Use it when building form validation rules, writing search-and-replace operations, parsing log files, extracting data from structured text, or building URL routing patterns. It is also an excellent learning tool for anyone studying regular expressions, as the instant visual feedback helps you understand how patterns match text. QA engineers use it to verify that validation patterns catch edge cases correctly.
Frequently Asked Questions
Which regex flavour does this tool use?
The tool uses JavaScript's built-in RegExp engine, which follows the ECMAScript specification. This is compatible with regex patterns used in most web development contexts, including Node.js, TypeScript, and browser-based JavaScript.
Can I test regex with flags?
Yes. You can toggle the global (g), case-insensitive (i), multiline (m), dotAll (s), and unicode (u) flags using the buttons provided. The tool updates matches in real time as you change flags.
Does it show capture groups?
Yes. When your pattern includes capturing groups using parentheses, the tool displays each group's matched content separately, making it easy to verify that your groups capture the correct portions of text.
Can I use this for regex in other languages?
JavaScript regex syntax is very similar to regex in Python, Java, C#, and PHP. Most patterns you test here will work in those languages with minimal or no changes. However, some advanced features like lookbehind assertions may behave differently across languages.