Regex Tester

WHAT IT DOES This tool lets you test regular expressions interactively. You enter a regex pattern, choose flags (global, case-insensitive, multiline, dotall, unicode, sticky), and provide test text. The tool applies the regex, shows all matches with their index positions, displays capture groups, and highlights matches directly in the test text. It also shows syntax errors with clear messages and provides a match count. Perfect for developers, data analysts, or anyone working with pattern matching and text processing. WHERE IT RUNS Runs on any website—no per-site configuration needed. Works entirely in the browser, so your regex and test text never leave your machine. The panel can be opened on any page, making it a convenient tool for quick regex testing without opening a separate tool or terminal. HOW TO USE Install the userscript via BotGentz, then open the panel. Enter your regex pattern in the first input field (without delimiters—just the pattern). Select the flags you need using the checkboxes: g (global), i (case-insensitive), m (multiline), s (dotall), u (unicode), y (sticky). Enter your test text in the large text area. The tool automatically tests the regex as you type (debounced) and displays results. You can also click "Test Regex" manually. The output shows a match count, the pattern and flags used, and a list of all matches with their index positions and capture groups. "Copy Matches" copies the full results to your clipboard. TECHNICAL MECHANISM The tool uses JavaScript's native RegExp constructor to compile the pattern with the selected flags. It first validates the pattern—if the constructor throws an error, the tool catches it and displays a clear error message. For testing, it uses either regex.exec() with the global flag to iterate through all matches, or regex.exec() once without global. When the global flag is set, it loops through exec() results until null, capturing the match index, value, and any capture groups. Zero-length matches are handled by incrementing lastIndex to prevent infinite loops. For highlighting, the tool builds a string by inserting tags around each match, escaping all text content to prevent XSS (PLAYBOOK-A §6 rule 3). All flags are stored in settings and persist across sessions via GM_setValue. THE PANEL The floating panel is built with BotGentz's BGPanel framework. It is draggable—click and drag the panel header to reposition it anywhere on the screen. The panel remembers its position per site via the settings dropdown. It can be collapsed to a small bubble icon by clicking the minimize button, preserving screen space. The panel can be closed and reopened via the BotGentz toolbar. Press the Escape key to quickly close the panel. The panel automatically adjusts its layout for different screen sizes. PLEASE NOTE Requires the free BotGentz extension. This tool processes text entirely in your browser and does not send any data to external servers. Regex patterns and test text are not stored or logged anywhere—only your flag preferences and settings are saved locally via GM_setValue. The tool uses JavaScript's regex engine, so it supports all standard JavaScript regex features but may differ from other implementations (PCRE, Python, etc.). Websites change frequently; if the tool stops working on a particular site, the script may need updating.