Regex Tester Online — Test & Debug Regular Expressions Free [2026]
Test and debug regular expressions online. Real-time match highlighting, group capture, flags support (g, i, m, s). Free regex tester with explanation.
What is Regex Tester?
How to Use Regex Tester
1. Enter your regular expression pattern in the "Regex" field (without slashes). 2. Select flags: g (global), i (case-insensitive), m (multiline), s (dotAll). 3. Paste or type your test string in the "Test String" area. 4. Matches are highlighted in real time as you type. 5. Scroll down to see captured groups and full match details. Tip: Start simple and build up your pattern incrementally — test after each change.
How Regex Tester Works
Common Use Cases
- Validating email addresses, phone numbers, or postal codes
- Extracting structured data from unstructured text
- Writing find-and-replace patterns in code editors
- Building input validation rules for web forms
- Parsing log files to extract specific fields
- Learning and experimenting with regex syntax
Frequently Asked Questions
What regex flavor does this tester use?▼
This tester uses JavaScript (ECMAScript) regex syntax, which is compatible with most modern programming languages. JavaScript regex supports: character classes, quantifiers, groups, lookahead/lookbehind, backreferences, and Unicode with the u flag. It does NOT support possessive quantifiers or atomic groups.
What do the flags g, i, m, s mean?▼
g (global): find all matches, not just the first. i (case-insensitive): match regardless of upper/lower case. m (multiline): ^ and $ match line starts/ends, not just string start/end. s (dotAll): . matches newlines in addition to other characters. Combine flags as needed, e.g., gi for global case-insensitive search.
How do I match a literal dot or parenthesis?▼
In regex, . * + ? ( ) [ ] { } \ ^ $ | are special characters. To match them literally, escape with a backslash: \. matches a literal dot, \( matches a literal open parenthesis. In a character class [ ], most special characters lose their meaning and don't need escaping.
What is a capture group?▼
A capture group ( ) extracts a specific part of a match. For example, (\d{4})-(\d{2})-(\d{2}) matches a date and captures the year, month, and day separately in groups 1, 2, and 3. Use (?:...) for a non-capturing group when you need grouping for quantifiers but don't need to capture the value.
Why does my regex work here but not in my code?▼
Common causes: (1) Backslash escaping — in JavaScript string literals, write \\d for \d (double-escape). In regex literals /\d/, no extra escaping needed. (2) Flags — ensure you're using the same flags in code as in the tester. (3) Engine differences — Python, PHP, Java have slightly different regex flavors. Test in the same language environment for final validation.
Related Tools
Explore More Free Tools
Discover more tools from our network — all free, browser-based, and privacy-first.