Free regex tester — free online regular expression testing tool with live matching. Test regex patterns for free. No registration required. Free regex validator and debugger online.
Test and debug regular expressions with live matching, syntax highlighting, and named group support. Works entirely in your browser — nothing is sent to any server.
Pattern
//
Flags
Quick
Test String
!
Match Highlight
Matching results will appear here
Matches
#
Index
Match
Named Groups
What the Regex Tester Does and Why It Matters
The Regex Tester lets you build and debug regular expressions against sample text, highlighting matches in real time and explaining what the pattern does. You can experiment with flags and capture groups and see results immediately.
Regular expressions are powerful but easy to get subtly wrong. Testing against real sample text — and seeing exactly what matches — is far faster and safer than guessing, especially before you put a pattern into production code.
How to Use Regex Tester
Enter your regular expression pattern.
Set any flags you need (global, case-insensitive, multiline).
Paste sample text to match against.
Watch matches highlight in real time as you edit.
Inspect capture groups and the explanation of the pattern.
Copy the working pattern into your code.
Supported Inputs and Limitations
What you provide
A regular expression pattern
Matching flags (g, i, m, etc.)
Sample text to test against
What you get
Highlighted matches in the sample text
Capture-group results
A plain-language explanation of the pattern
Known limitations
Regex flavours differ; a pattern tuned here uses JavaScript semantics, which can vary from PCRE or other engines.
Catastrophic backtracking in a poorly written pattern can be slow on large input.
It tests matching behaviour, not the performance characteristics of your final environment.
Privacy and Security
Pattern testing runs entirely in your browser; your expression and sample text are never sent to NovaTools and nothing is stored. You can test against real (non-secret) sample data privately.
Frequently Asked Questions
Which regex flavour does this use?
It uses the JavaScript regular-expression engine. Most syntax is portable, but features like look-behind support or named groups can differ from PCRE, Python, or other engines.
Why is my pattern matching too much or too little?
Common causes are a greedy quantifier that should be lazy, a missing or extra flag (such as global or multiline), or unescaped special characters. Watching the live highlights usually reveals which.
Is my sample text uploaded?
No. Matching happens locally in your browser, so your pattern and test data stay on your device.
Regular expressions (regex) are a powerful mini-language for matching, searching, and transforming text. This free online regex tester lets you write a pattern and instantly see all matches highlighted in amber inside your test string. Named capture groups are shown in a dedicated column so you can quickly verify complex patterns. Everything runs locally in your browser — no data ever leaves your machine.
How to Use
Type your regex pattern into the Pattern field between the two slashes.
Toggle the g i m s flags as needed. The g flag is always active to find all matches.
Use the Quick presets to load common patterns for Email, URL, IPv4, Date, or Phone.
Paste or type text into the Test String area — results update live on every keystroke.
Scroll down to the Matches table to inspect each match's index, value, and any named groups.
Frequently Asked Questions
What regex flavour does this tester use?
This tool uses JavaScript's built-in RegExp engine, which follows the ECMAScript specification. It supports character classes, quantifiers, lookaheads/lookbehinds, and named capture groups.
What does the "g" flag do?
The global (g) flag tells the engine to find all matches rather than stopping after the first one. This tester always uses the g flag internally so the match count and table are always complete.
How do named capture groups appear?
If your pattern includes named groups such as (?<year>\d{4}), the Named Groups column in the match table will show each group name paired with its captured value for every match.
Is my data kept private?
Yes. All regex evaluation happens entirely in your browser using native JavaScript. No pattern, test string, or result is ever sent to any server or stored anywhere outside your current browser tab.
Why does my regex throw an error?
A red error banner appears when the browser's RegExp constructor cannot parse your pattern. Common causes include unescaped special characters, mismatched parentheses, or unsupported syntax. The banner shows the exact error message to help you fix it quickly.
Recommended next reading
Use these practical guides to understand when this tool is the right choice, what to check before exporting, and which workflow usually comes next.
