# Regex Tester Test regular expressions against text > Canonical page: https://elysiatools.com/en/tools/regex-tester - **Category:** Development - **Keywords:** regex, tester, test, regular expression, regex tester ## Overview The Regex Tester is a streamlined utility designed to help developers and data analysts validate regular expression patterns against sample text in real-time. By providing an immediate visual breakdown of matches, groups, and flags, this tool ensures your regex logic is accurate before you implement it in your codebase. ## Inputs - **Regex Pattern** (text): Enter regex pattern... - **Flags** (text): g, i, m, etc. - **Test Text** (textarea): Enter text to test against... - **Show All Matches** (checkbox) ## When to use - Validating complex search patterns for data extraction or text processing tasks. - Debugging regex syntax errors when your application fails to capture expected strings. - Testing how different regex flags, such as global or case-insensitive, affect your matching results. ## How it works - Enter your regular expression pattern into the Regex Pattern field. - Input the target text you wish to analyze in the Test Text area. - Apply optional flags like 'g', 'i', or 'm' to refine your search behavior. - View the highlighted matches and capture groups instantly to verify your logic. ## Use cases - Extracting email addresses or phone numbers from unstructured log files. - Validating user input formats like dates, postal codes, or usernames. - Refactoring large blocks of text by identifying specific patterns for replacement. ## Frequently asked questions ### What regex engine does this tool use? This tool utilizes the standard JavaScript RegExp engine, which is compatible with most modern web browsers and Node.js environments. ### Can I use capture groups in my patterns? Yes, the tool supports standard capture groups, and you can view the captured content in the results output. ### What do the flags 'g', 'i', and 'm' do? 'g' enables global matching, 'i' makes the search case-insensitive, and 'm' enables multiline mode. ### Is my data stored on your servers? No, all regex testing is performed locally in your browser, ensuring your input text remains private. ### Why is my regex not matching anything? Check for syntax errors, ensure your flags are correct, and verify that your pattern logic matches the structure of your test text. ## Related tools - [PCRE2 Regex Tester](https://elysiatools.com/en/tools/pcre-regex-tester): Test PCRE2 patterns online: every named-group syntax ((?P), (?), (\\u0027n\\u0027)), possessive quantifiers, atomic groups, \\A \\z \\h shorthands, plus pcre2grep and C API snippets. - [Regex Debugger](https://elysiatools.com/en/tools/regex-debugger): Step through how a regular expression matches a string position by position: visualize match attempts, partial successes, backtracks, and captures — a learning tool for understanding regex behavior, not just the final result - [AI Regex Explainer](https://elysiatools.com/en/tools/ai-regex-explainer): Use AI to break down regular expressions into readable explanations - [C# Regex Tester (.NET)](https://elysiatools.com/en/tools/csharp-regex-tester): Test .NET/C# regular expressions online with named groups ((?…)), IgnoreCase/Multiline/Singleline options, match highlighting, capture-group tables, a ready-to-paste C# snippet and an IgnorePatternWhitespace preview. - [Java Regex Tester](https://elysiatools.com/en/tools/java-regex-tester): Test java.util.regex patterns online: (?…) named groups, possessive quantifiers and atomic groups, Pattern flags, ASCII vs UNICODE\_CHARACTER\_CLASS \\d semantics, and ready-to-paste Java code. - [Python Regex Tester (re module)](https://elysiatools.com/en/tools/python-regex-tester): Test Python re patterns online: (?P…) named groups, (?P=name) backreferences, VERBOSE patterns, findall behavior, and \\g replace templates — plus ready-to-paste Python code. - [Regex Cheat Sheet](https://elysiatools.com/en/tools/regex-cheat-sheet): A searchable, localized cheat sheet for regular expression syntax — character classes, anchors, quantifiers, groups & references, lookarounds, escape sequences, and flags — with a built-in quick tester - [Regex to String Generator](https://elysiatools.com/en/tools/regex-to-string-generator): Generate random strings that match a given regular expression pattern ## Samples - [Regex Replace Samples](https://elysiatools.com/en/samples/regex-replace): Collection of common and useful regex replacement patterns for text transformation and data cleaning - [Common Regex Patterns](https://elysiatools.com/en/samples/regex-samples): Commonly used regular expression patterns for validation and matching - [Regex Pattern Alternatives](https://elysiatools.com/en/samples/regex-alternatives): Multiple ways to write the same regex pattern with different trade-offs in readability, performance, and accuracy - [Regex Named Capture Groups](https://elysiatools.com/en/samples/regex-named-groups): Collection of regex patterns using named capture groups for extracting structured data from text. Named groups make patterns more readable and maintainable by assigning meaningful names to captured portions. ## Related content - [Regex Testing, Visualization, and Safety Workflow](https://elysiatools.com/en/hubs/regex-utility): Build reliable regular expressions by learning syntax, testing matches, visualizing structure, previewing replacements, benchmarking alternatives, and scanning for ReDoS risk.