What is a Regex Tester?
A regex tester (regular expression tester) is an interactive tool that lets you write and test regular expression patterns against sample text, with real-time match highlighting. Regular expressions (regex or regexp) are sequences of characters that define a search pattern — used to find, validate, extract, and replace text in strings. Regex is supported by virtually every programming language (JavaScript, Python, PHP, Java, Ruby…) and many text editors.
Developers use regex to validate email addresses and phone numbers in form inputs, extract data from API responses and log files, find and replace text in code editors, parse HTML and structured text, and sanitise user input. Regex can be notoriously difficult to write correctly from memory — our tester lets you experiment interactively, see highlighted matches in real time, and build confidence in your pattern before adding it to code.
How to Use the Regex Tester
- Enter your regular expression in the Regular Expression field (between the / / delimiters).
- Enter regex Flags (g for global, i for case-insensitive, m for multiline, s for dotAll).
- Optionally load a Quick Pattern example (email, URL, phone, IP, date, HEX color).
- Type or paste your Test String — matches are highlighted in yellow in real time with a match count and list.
Why Use Our Regex Tester?
- 100% Free — Test unlimited regex patterns.
- No Registration — No sign-up required.
- Browser-Based — Uses JavaScript's native RegExp engine — your text never leaves your device.
- Live Highlighting — Matches are highlighted in real time as you type — instant visual feedback.
- Quick Patterns — Load common patterns (email, URL, phone, IP address, date) with one click.
Frequently Asked Questions
g (global) — find all matches, not just the first. i (case-insensitive) — match regardless of letter case. m (multiline) — ^ and $ match start/end of each line, not just the whole string. s (dotAll) — the dot (.) matches newline characters too. Combine flags (e.g. "gi") for multiple behaviours simultaneously.
In most regex flavours, \d and [0-9] are equivalent — both match a single digit character 0–9. In some Unicode-aware engines, \d can also match digits from other scripts (Arabic-Indic, Devanagari). In JavaScript with the "u" flag, \d still matches only ASCII digits. For maximum clarity and portability, [0-9] is explicit; \d is a convenient shorthand.
The dot (.) in regex is a metacharacter that matches any single character except newlines. To match a literal dot (e.g. in an IP address like 192.168.1.1), escape it with a backslash: \. — so the pattern becomes 192\.168\.1\.1. Always escape metacharacters (. * + ? ^ $ {} [] | \) when you want to match them literally.
Without the "g" flag, String.match() returns only the first match. With "g", it returns all matches as an array. Similarly, String.replace() with "g" replaces all occurrences, not just the first. Without "g", String.matchAll() throws an error. This tester automatically adds "g" to your flags if not present to ensure all matches are highlighted.