Writing regular expressions from memory is painful — even experienced developers test and iterate in a live environment. Our free regex tester online gives you real-time match highlighting, capture group visualization, and a full match table as you type your pattern. Supports JavaScript, Python, PHP, and PCRE regex flavors. Paste your test string, type your regex, and see every match highlighted instantly — no page reload, no account, no data sent to any server. Whether you're writing email validation, parsing log files, extracting data from text, or building a search feature, this tool cuts regex development time dramatically.
How to Use the Regex Tester
- Enter your regex pattern in the pattern field (without the surrounding slashes)
- Set your flags — g (global), i (case-insensitive), m (multiline), s (dotAll) using the flag checkboxes
- Paste your test string in the text area below
- Matches highlight automatically — each match is highlighted in the test string as you type
- Review the match table to see full matches, capture groups, and their positions
- Select regex flavor (JavaScript, Python, PHP) to switch between flavor-specific syntax
What Is a Regex Tester?
Regular expressions (regex) are patterns that describe sets of strings. They're used in virtually every programming language for searching, validating, extracting, and replacing text. A regex tester is an interactive tool that shows you the results of a regex against a sample input in real time — so you can iterate on your pattern without writing, running, and re-running code.
The key advantage of an online regex tester over testing in code is speed: you see the match result instantly as you type each character of your pattern. This makes it much faster to debug why a pattern isn't matching, identify edge cases, and verify that your regex handles all the input variations you need to handle.
Common regex use cases
- Input validation — email addresses, phone numbers, postal codes, credit card numbers
- Log parsing — extracting timestamps, IP addresses, error codes from log files
- Data extraction — pulling URLs, prices, or specific fields from unstructured text
- Search and replace — finding patterns in code editors and transforming text in bulk
- URL routing — matching URL patterns in web frameworks like Express, Django, Laravel
Why Use PromptSpace's Regex Tester?
- ✅ Real-time matching — matches highlight instantly as you type your pattern
- ✅ Capture group visualization — each capture group is shown with its matched text and position
- ✅ Multiple flavors — JavaScript, Python, PHP/PCRE with flavor-specific syntax handling
- ✅ Match table — see all matches with start/end positions at a glance
- ✅ Flag support — global, case-insensitive, multiline, dotAll, Unicode flags
- ✅ Free, no signup, browser-side
Frequently Asked Questions
What regex flavors are supported?
The tester supports JavaScript (ECMAScript), Python (re module), and PHP/PCRE regex. Each flavor has slight syntax differences — for example, Python uses (?P<name>) for named groups while JavaScript uses (?<name>). Select your flavor to get accurate results.
How do I match a literal dot, bracket, or other special character?
Escape it with a backslash: . matches a literal dot, [ matches a literal bracket, ( matches a literal parenthesis. In the regex tester, you enter the pattern without surrounding slashes — just the pattern itself, like d{3}-d{4}.
Why does my regex match too much or too little?
Check your quantifiers: * is greedy and matches as much as possible, while *? is lazy and matches as little as possible. Also check your anchors: ^ matches start of string (or line with m flag), $ matches end. Missing anchors often cause patterns to match inside longer strings when you only want full-string matches.
Can I save and share my regex patterns?
The tester generates a shareable URL containing your pattern, flags, and test string — copy the URL from your browser's address bar to share your exact regex setup with a colleague.
Related Free Tools
- Free JSON Validator — Validate JSON schemas that often use regex patterns for string validation
- Free URL Encoder/Decoder — Encode strings that regex patterns will be matched against in URLs
- Free Hash Generator — Generate test strings to verify your regex handles hashed values correctly
