Precision-engineered regex tester for the modern web.
About Regex tester
Regex tester is a regex workspace built for developers who refuse to guess. Write a pattern, paste a sample input, and the tool shows you every match in real time with named groups, capture indices and a human-readable breakdown of what the pattern is actually doing. It tests against ECMAScript, PCRE and Python-compatible flavours so you can verify a regex once and know it will behave consistently across the languages in your stack. Because everything runs on-device, you can safely test against sample data that contains credentials or PII.
Problems This Tool Solves
Regexes that "work in one language" often silently misbehave in another. - Regex tester tests your pattern against JavaScript, PCRE and Python flavours and flags incompatible constructs.
Debugging a failing regex by trial-and-error is slow and frustrating. - Regex tester explains every token in the pattern and highlights exactly why a match did or did not happen.
Regex catastrophic backtracking can freeze a server on production input. - Regex tester analyses your pattern for exponential backtracking risk and warns you before you ship.
Pasting data into an online tool means trusting a third-party server with your content. - Regex tester runs 100% inside your browser — nothing you paste is transmitted, logged, or stored.
How to Use
Enter your pattern - Write or paste a regex, with flag toggles for global, case-insensitive, multiline and unicode.
Paste your input - Drop any sample text — long logs, CSV dumps or multi-line documents.
Inspect matches live - Every match highlights in the input with captured groups annotated in a side panel.
Export code - Generate a ready-to-paste regex literal for your target language with escaping handled.
Why This Tool Is Better
Cross-flavour validation - Tests the same pattern against JavaScript, PCRE and Python to catch incompatibilities early.
Readable token breakdown - Each character class, quantifier and group is annotated so you can debug without a reference manual.
Private testing - Because everything is local, you can test against real production samples that contain tokens or PII.
Category: Dev & Encoding Tools
This tool runs entirely in your browser. No data is sent to any server. Try the Regex tester now - it is free.