Regex Tester
Test and debug regular expressions with live match highlighting.
Runs in your browser
Your files and text are processed locally in your browser and are not uploaded.
About Regex Tester
A Regex Tester is a utility that compiles regular expression patterns and tests them against target strings. It highlights matches and identifies capture groups, helping developers validate patterns for input validation, text search, and web development.
Definition: Regular Expression (Regex)
A sequence of characters that forms a search pattern. It is used in pattern matching, search-and-replace operations, and data validation across programming languages.
Inputs and Outputs
Required Inputs
- Regular ExpressionThe search pattern (e.g., ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,5}$).
- FlagsSelect checkboxes for global (g), case-insensitive (i), multiline (m), and single line (s).
- Test StringThe text block to test and match against the regex pattern.
Expected Outputs
- Matches HighlightedTest string with highlighted matches.
- Capture Groups ListList of match details and capture groups.
- Syntax ValidationReal-time compile error alerts for invalid regex syntax.
Who Uses the Regex Tester?
Form Validation Development
Build and test patterns to validate email addresses, phone numbers, zip codes, and password strength.
Log Analysis
Create patterns to parse log files, extract IP addresses, extract timestamps, or find specific error messages.
Data Extraction
Write capture group patterns to extract text from HTML, XML, CSV, or markdown payloads.
Search-and-Replace Logic
Develop search patterns to perform complex search-and-replace operations in text editors.
How to Use the Regex Tester
- 1Enter your regex pattern in the expression input field (exclude the slashes).
- 2Select your required flags (like global 'g' or case-insensitive 'i') from the toggles.
- 3Enter your test text in the text area below.
- 4Review the highlighted matches and capture groups shown in the results panel.
Quick Facts
Privacy & Security Guarantee
All regular expression testing runs entirely in your local browser engine. No search strings or expressions are uploaded to Zynocode servers.
Frequently Asked Questions
What do the regex flags g, i, and m do?
Flags modify search behavior: 'g' (global) returns all matches instead of stopping after the first one; 'i' (case-insensitive) ignores capitalization; 'm' (multiline) treats beginning and end characters (^ and $) as working across multiple lines.
Which regex engine does this tool use?
This tool uses the browser's native JavaScript RegExp engine. While JavaScript regex is similar to PCRE (Perl Compatible Regular Expressions), some advanced features (like lookbehinds) may differ depending on your browser version.
How do I escape special characters in regex?
Characters like ., *, +, ?, ^, $, (, ), [, ], {, }, |, and \ have special meanings in regex. To match these characters literally, escape them with a backslash (e.g., use \. to match a literal period).
What are capture groups?
Capture groups are defined by wrapping a part of the regex pattern in parentheses `(...)`. They isolate parts of the matched string for search-and-replace operations or extraction.
Can this tool cause browser crashes from infinite loops?
Certain regex patterns (especially nested quantifiers like `(a+)+`) can cause catastrophic backtracking, making the browser lag. If this happens, your browser may prompt you to stop the page execution.
Are my test strings sent to Zynocode's servers?
No. The regex compilation and testing are executed locally in your browser. Your regex patterns and test strings are never sent over the internet.