Charles

Charles is a specialized HTTP proxy, HTTP monitor, and reverse proxy tool designed for web developers and software engineers to inspect, debug, and control all HTTP and HTTPS traffic flowing between a client machine and remote servers. It captures every request and response exchanged by applications such as browsers, mobile apps, and API clients, presenting them in a structured, real-time interface. Users can examine raw headers, cookies, caching directives, query parameters, and response bodies including JSON, XML, images, and binary data. The tool supports SSL/TLS interception (SSL proxying) by dynamically generating certificates, allowing developers to decrypt and view encrypted HTTPS traffic for debugging purposes. This is critical for troubleshooting authentication flows, verifying certificate chains, and ensuring secure data transmission in staging environments. Charles also provides advanced traffic manipulation features. With breakpoints, users can pause a request or response, modify headers or body content on the fly, and then resume the exchange to test client or server behavior under altered conditions. The "Map Remote" and "Map Local" functions let developers redirect requests to different servers or local files without changing application code, enabling quick mocking of APIs or testing fallback logic. Auto-response rules can be configured to return predefined data for specific request patterns, which is useful for simulating error scenarios or offline conditions. Bandwidth throttling simulates slow network connections (e.g., 3G, DSL, high-latency links) to evaluate application performance under constrained environments. For systematic debugging, Charles records all traffic into sessions that can be saved, replayed, and compared.