Opal DevTools is a free Chrome extension that integrates a Ruby REPL directly into the browser's developer tools. This tool allows users to execute Ruby code in real-time while interacting with any web page. Key features include Pry-like commands for navigating and exploring objects, multi-line input support, and command history accessible via arrow keys. The extension auto-injects the Opal runtime, making it easy to work with pages that already have Opal loaded.

Users can access the Opal REPL by opening the DevTools and selecting the dedicated tab. It supports various commands such as 'ls' for listing methods and 'cd' for changing context. However, it is important to note that the extension may not work on pages with strict Content Security Policies that block 'unsafe-eval'. This tool is open-source and prioritizes user privacy by executing all code locally.