What is the difference between a SOAP API and a REST API? Is one better than the other?

SOAP (Simple Object Access Protocol) and REST (Representational State Transfer) are two different types of web service architectures, each with its own set of advantages and disadvantages. Here are some of the key differences between the two:

1. Protocol: SOAP is a protocol, while REST is an architectural style. SOAP uses the XML format for its message protocol, while REST typically uses JSON.

2. Communication: SOAP uses XML to transport data over the internet, while REST uses HTTP.

3. WSDL: SOAP requires a WSDL (Web Services Description Language) file to define the contract between the client and server. REST does not require this file.

4. Payload: SOAP has a large overhead due to the use of XML, which means larger message payloads. REST has a smaller overhead, which means smaller message payloads.

5. State: SOAP has built-in stateful operations, while REST is stateless.

6. Caching: RESTful APIs can leverage browser caching, while SOAP APIs cannot.

7. Flexibility: RESTful APIs are more flexible than SOAP APIs, as they can work with a variety of data formats and can be easily used with multiple programming languages.

As for which one is better, it really depends on the specific use case. SOAP is often preferred for enterprise-level applications, as it has built-in error handling and is more secure than REST. However, it can be more complex to work with and has a larger overhead. REST, on the other hand, is simpler to work with and is often used for mobile and web applications. It's also easier to scale and has better caching support. Ultimately, the decision of which to use will depend on the specific requirements of the project.