Regex Tester

What Is a Regex Tester?

This free regex tester lets you test regular expressions against any text in real time. It shows match count, lists all matched strings, and displays clear error messages for invalid patterns — all as you type, with no button press needed. Whether you are a developer writing input validation, a data analyst extracting patterns, or a student learning regex syntax, this regex tester makes pattern testing instant and transparent.

In fact, regex is notoriously difficult to write correctly without testing. Even experienced developers test patterns before using them in production code. This regex tester eliminates trial and error by showing live results and listing every match individually.

How Does This Regex Tester Work?

This regex tester applies your pattern and flags to the test string using JavaScript’s built-in RegExp engine. It finds all matches using the global flag, counts them, and lists the first 20 matched strings individually. Any invalid regex syntax is caught immediately and shown as a clear amber error message — the regex tester never fails silently.

Regex Flags in This Regex Tester

• g (global): Find all matches in the string, not just the first. This regex tester uses g by default to show all results.
• i (case-insensitive): Match regardless of letter case. The pattern “hello” with the i flag matches “Hello”, “HELLO”, and “hello”.
• m (multiline): Makes ^ and $ match the start and end of each line, not just the beginning and end of the whole string.
• s (dotAll): Makes the dot (.) match newline characters as well as all other characters.
• u (unicode): Enables full Unicode support, including correct handling of surrogate pairs and Unicode escape sequences.

Quick Pattern Presets in This Regex Tester

This regex tester includes one-click presets for the most common patterns. Click any preset to load it instantly and test it against your string.

• Email: Matches standard email address formats. Not 100% RFC-compliant but covers virtually all real-world addresses.
• URL: Matches http and https URLs including query strings and fragments.
• Date (YYYY-MM-DD): Matches ISO 8601 date format. Useful for validating date fields in forms and APIs.
• HEX Colour: Matches 6-digit hex colour codes with a # prefix. Useful for CSS parsing and design tooling.
• Integer: Matches any sequence of digits. Combine with ^ and $ anchors in this regex tester for full-string matching.

Is This Regex Tester Accurate?

This regex tester uses JavaScript’s ECMAScript RegExp engine — the same engine used in Node.js, Chrome, Firefox, and Safari. According to the MDN Regular Expressions guide, JavaScript regex supports the full ECMAScript standard. Minor differences exist between JavaScript regex and PCRE (used in PHP and Perl) — always verify critical patterns in your target environment, but for most use cases this regex tester gives accurate results.

Common Regex Tester Mistakes to Avoid

• Forgetting the g flag: Without g, the regex tester only shows the first match. Add g to the flags field to see all matches.
• Unescaped special characters: Characters like . * + ? ( ) [ ] { } ^ $ | \ have special meaning in regex. Use a backslash to match them literally — for example, \. to match a literal dot instead of “any character”.
• Case sensitivity: Regex is case-sensitive by default. Add the i flag in this regex tester to match regardless of case.
• Greedy vs lazy quantifiers: By default, * and + are greedy — they match as much as possible. Add ? after them (.*?) to make them lazy and match as little as possible.

Regex Tester — Frequently Asked Questions