100% Client-side processing. Your data never leaves your browser.
Test regular expressions with real-time match highlighting, capture group extraction, replace output, and cheatsheet insertions.
A secure, browser-based utility for interactive regular expression testing and visualization. Test your patterns and sensitive text safely without sending data to external servers.
Instantly color-codes matched text as you type the pattern, flags, or test string. Groups defined by parentheses () (Group 1, Group 2, etc.) are extracted individually in a list to simplify complex pattern verification.
Type a replacement string to see the result updated in real time, and copy it with a single click. A sidebar cheatsheet lets you quickly insert common patterns like email addresses, URLs, and digits.
All parsing, highlight rendering, and replacements are executed locally inside your browser via JavaScript. Your test string or pattern is never sent over the network.
A Regex Tester (also called a Regular Expression Tester or Regex Checker) is a tool that lets you verify in real time which parts of your input text match a given regular expression pattern. Developers searching for "regex tester" or "regex online" all share the same core need: they want to see the behavior of their regex patterns with their own eyes.
Regular expressions are an incredibly powerful mechanism. With just a few characters, you can search, extract, replace, and validate strings. But that power comes at a cost: poor readability. Once a pattern grows even slightly complex, it can become nearly indecipherable — often jokingly referred to as "black magic." Even the original author may struggle to explain what a pattern matches just a few weeks later.
Regex-specific bugs deserve special attention. A classic example is the greedy match problem. If you try to extract HTML tags with a pattern like <.*>, the .* will match as much text as possible, potentially spanning multiple tags and capturing unintended content. Similarly, a self-written regex for email validation may contain a single typo or oversight that lets invalid input slip through.
The scariest part? Many of these issues only become apparent after the code is deployed. Discovering that a production validation isn't working correctly and scrambling to issue an emergency fix is a scenario every developer wants to avoid. By using a browser-based regex tester to verify pattern behavior in real time before integrating it into your codebase, you can significantly reduce debugging lead time.
Once you enter both a regex pattern and a test string, matching locations are dynamically highlighted with every keystroke. Since you can see the updated result every time you tweak the pattern, there is no need for the traditional "save, run, check the output" loop. This real-time regex testing experience is at the heart of our tool's philosophy: "know the answer the moment you think of the question."
For example, when building a regex for phone number or email validation, an effective workflow is to prepare both valid and deliberately invalid test strings, then observe the regex match behavior for both simultaneously. Even for common requirements like email regex validation, testing against real input data in real time dramatically reduces the risk of overlooking unexpected edge cases.
Portions of a regex enclosed in () are called "capture groups," used to extract specific parts of a matched string. However, when groups are nested or numerous, visually tracking which group extracts what becomes challenging.
Our tool highlights each regex capture group in a different color, allowing you to instantly see which () corresponds to which extracted text. In practical log analysis, regex patterns often extract elements like timestamps, log levels, and message bodies into separate capture groups. With our tool, you can confirm that each group extracts the intended text as you build the pattern.
The "Replace" feature also operates in real time. Beyond simple string replacement, it supports capture group references like $1 and $2, letting you see the output before executing the replacement in your actual code.
This directly addresses the need for regex replace online. Practical use cases include log cleansing (bulk removal of unwanted text), standardizing CSV delimiters, and normalizing phone number formats (e.g., unifying hyphen usage). By testing replacement behavior before integrating it into production scripts, you can prevent unintended data corruption.
Flags that control regex behavior (global g, case-insensitive i, multiline m, etc.) can be toggled intuitively using checkboxes. Since you can compare how the match results change with and without each flag in real time, this is also an excellent way to learn the practical effect of each flag hands-on.
Regex testing often involves sensitive input: production server logs, phone numbers or email addresses from customer lists, and source code containing credentials. Many organizations have security policies that explicitly prohibit pasting confidential data into external online services.
All text and regex patterns entered into our tool are processed exclusively within your browser via JavaScript. No data is ever transmitted to an external server. You can verify this first-hand by opening your browser's Developer Tools (Network tab) while using the tool. Because no server communication ever occurs, there is structurally no risk of your data being stored, logged, or analyzed by any third party.
No account registration or app installation is needed. Whether you use it daily as a JavaScript regex tester, simply open the URL in your browser and start working instantly. There are no distracting ads, and the convenience of one-click access from your bookmarks makes it a natural part of any developer's daily workflow. As a free regex tool, we impose no feature restrictions or usage limits — everything is available indefinitely, at no cost.
A Regex Tester is a tool that lets you verify in real time which parts of your input text match a given regular expression pattern. Also known as a Regular Expression Tester or Regex Checker, it provides features such as match highlighting, visual capture group extraction, and replacement simulation — giving you a comprehensive view of your regex behavior.
No, it is never transmitted. All text and regex patterns entered into our tool are processed exclusively within your browser using client-side JavaScript. They are never sent to or stored on our servers or any third-party servers. You can verify this yourself by opening your browser's Developer Tools (Network tab) to confirm that no external requests are made.
Yes, both are supported. Capture groups enclosed in () are each highlighted in a distinct color, letting you see at a glance which part is being extracted. Additionally, when you enter a replacement pattern using group references like $1 or $2, the output is displayed in real time so you can verify behavior before integrating it into production code.
Yes. You can test your patterns against commonly used regex samples — such as email addresses, URLs, and phone numbers — directly within the tool. Instead of writing a pattern from scratch, you can start from a sample and adjust it to fit your specific requirements. This approach reduces the learning curve while helping you build the right pattern efficiently.
