Proxy Checker is a subscription-based extension for Firefox designed for web developers and IT professionals who utilize web proxies. This tool simplifies the evaluation of proxy IP addresses, allowing users to input a list of HTTP proxies for thorough testing. Once the proxy list is submitted, the extension connects to each proxy to assess its performance and security features, ensuring that users have reliable access to web resources.

The extension provides a detailed report on each proxy's quality, which includes insights from various databases, DNS checks, and header leak evaluations. By generating a calculated quality score, Proxy Checker helps users identify poor-quality proxies that may cause disruptions or limitations in web access. This functionality is essential for those looking to optimize their proxy usage and make informed decisions about their network configurations.