Rubric is a free Chrome add-on developed by Rickard Andersson that allows users to inject custom HTTP request and response headers into their browser requests. This tool is particularly useful for web developers, as it enables them to test and debug their websites by simulating different scenarios.

With Rubric, users can easily add custom headers to their requests, providing them with greater control and flexibility during web development. By injecting custom headers, developers can simulate specific user-agent strings, modify cookie values, or manipulate request headers to test different server responses.

Furthermore, Rubric is also valuable for privacy and security researchers. It allows them to analyze how websites handle different headers and responses, helping them uncover potential vulnerabilities or privacy concerns.

Overall, Rubric is a powerful Chrome add-on that empowers web developers and researchers to inject custom headers into their browser requests. Its user-friendly interface and extensive customization options make it a valuable tool for testing, debugging, and privacy and security research.