Free Regex Tester
Test and debug regular expressions — 100% free in your browser.
Free How to use Regex Tester
Developer utilities perform pure text transformations—JSON formatting, Base64 encoding, hash generation, JWT decoding, regex testing, and code minification—entirely in JavaScript within your browser. No snippets, tokens, or configuration payloads are sent to a backend because these tools operate on strings already present in the page. That design is ideal when you are inspecting production JWTs, hashing passwords for comparison, or minifying proprietary templates: your input stays in local memory and is discarded when you navigate away. The tools are deterministic and offline-capable once the page has loaded.
What Regex Tester does and when to use it
Regex Tester lets you experiment with regular expressions against sample strings, highlighting matches and capture groups for data validation, log parsing, and refactor-safe find-replace planning. It beats editing code blindly when patterns grow complex with lookaheads and named groups.
Support engineers extract ticket IDs from emails, data engineers prototype field extractors, and students learn pattern syntax interactively with immediate feedback on failing cases.
How this tool works
The tester compiles patterns with JavaScript RegExp engines in the browser, running global and multiline flags you toggle in the UI. Match indices colorize substrings; group extracts populate side panels.
Test strings never leave your session. Catastrophic backtracking on evil patterns can freeze the tab—use possessive quantifiers sparingly and test modest input sizes first.
Step-by-step instructions
Enter a regex pattern and flags, paste a sample string, and observe highlighted matches. Refine the pattern until edge cases pass, then copy the working expression into your codebase.
Tips and best practices
Include negative test cases—strings that should not match—to avoid overfitting.
Remember JavaScript regex flavors differ slightly from PCRE used in other languages.
Learn more: Base64, Hashes, JWTs, and Developer Encoding Tools
Regex Tester FAQ
Answers to common questions about Regex Tester.
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