Which data format is commonly used with HTTP Callouts?

The commonly used data format with HTTP Callouts is JSON. This is due to its lightweight structure, making it easy to read and write as well as easy for machines to parse and generate. JSON's compatibility with JavaScript also makes it a preferred choice for web applications that rely on dynamic content and frequent data exchanges.

Additionally, JSON's format allows for complex data structures, including nested objects and arrays, which can represent detailed and structured data efficiently. This adaptability aligns well with RESTful services, which are commonly used in HTTP Callouts, as they often return data in JSON format.

While XML is also used with HTTP Callouts, it tends to be more verbose and complex, making JSON the more favored format in many modern applications. On the other hand, YAML's syntax can be beneficial for configuration files but is less common in API interactions. CSV is primarily suited for tabular data and doesn't align as well with the hierarchical data often exchanged in web services. Thus, JSON’s efficiency and ease of use cement its status as the preferred format for HTTP Callouts.