How to Test Regular Expressions Online
- 1
Enter your regex pattern
Type or paste your regular expression into the pattern field. The tool accepts any valid JavaScript regex syntax including character classes, quantifiers, groups, and lookaround assertions. - 2
Set regex flags
Toggle the flags you need: Global (g) to find all matches, Case Insensitive (i) to ignore letter casing, Multiline (m) so ^ and $ match line boundaries, and Dot All (s) so the dot matches newline characters. - 3
Add your test string
Paste or type the text you want to test against your pattern. You can add multiple test strings to validate your regex against different inputs simultaneously. Matches are highlighted in real time as you type. - 4
Review matches and capture groups
Inspect the highlighted matches in the output panel. Each match shows its position index and any captured groups. Adjust your pattern or flags until the results match your expectations, then copy the working regex into your code.
Common Use Cases
Email Validation
Data Extraction
Search and Replace
Log Parsing
Why use our Regex Tester?
Regular expressions are one of the most powerful text processing tools in a developer's toolkit. This free online regex tester lets you write, test, and debug regex patterns with instant visual feedback. Every match is highlighted in real time as you type, and capture groups are displayed with their index positions so you can verify extraction logic before writing a single line of code.
The tool runs JavaScript's regex engine, which covers the vast majority of real-world patterns. Most regex syntax -- character classes, quantifiers, alternation, lookahead, lookbehind, and named groups -- is shared across JavaScript, Python, PHP (PCRE), Java, and Go. If your pattern works here, it will almost certainly work in your target language. For differences between engines, always consult the documentation for your specific runtime.
Whether you are validating user input, parsing log files, extracting data from HTML, or building search-and-replace transformations, testing patterns interactively saves significant debugging time. Pair this tool with the Glob Pattern Tester for file path matching, or use the Diff Checker to compare before-and-after results of a regex replacement. All processing runs entirely in your browser -- nothing is uploaded to any server, so your data stays private.