RESTSOAPHTTPAPI Designjunior level

REST and SOAP Solve API Design Differently

the question

What is the difference between REST and SOAP, and when would you choose one over the other?

what they're testing: The interviewer is checking whether you can separate an architectural style from a messaging protocol and reason about the resulting API trade-offs.

a strong answer

REST and SOAP solve different problems. REST is an architectural style built around resources, representations, a uniform interface, and stateless interactions. SOAP is a protocol with an XML-based message structure, processing rules, faults, extensibility, and a framework for binding messages to an underlying protocol.

In the common HTTP case, a REST API identifies resources and follows HTTP semantics for methods, status codes, headers, and representations. JSON is popular, but REST does not require it. SOAP messages keep their own envelope and processing rules. They can be carried using different underlying protocols, with HTTP as one option. WSDL is a separate XML language that can describe a service's interface, bindings, and endpoints.

Choose REST when the API benefits from the Web's uniform interface, intermediaries, caching, and independent evolution of clients and servers. Choose SOAP for an existing SOAP integration or an ecosystem that depends on SOAP extensions and contract-oriented tooling. Neither is inherently faster or more secure. Payloads, transport security, extensions, implementation, and API design determine those properties.

Where people slip

the tempting wrong answer, and what's actually true

REST is a protocol that uses JSON, while SOAP is a protocol that uses XML.
REST is an architectural style and does not require JSON, while SOAP specifies an XML-based message construct and processing model.
SOAP only works over HTTP.
SOAP defines a binding framework for underlying protocols, with HTTP being one available binding.
SOAP is always more secure than REST.
SOAP is not inherently more secure than a REST API. SOAP's core messaging specification omits security, so actual security depends on the transport, extensions, authentication, and implementation.

If they push further

Does a REST API have to use HTTP and JSON?

No; REST is not tied to one protocol or representation format, although HTTP and JSON are the common API combination.

What does stateless mean in REST?

Each request carries the information needed to understand it without relying on server-side application context from earlier requests.

Is WSDL required for SOAP?

SOAP defines messaging, while WSDL is a separate service-description language that can describe SOAP interfaces and bindings.

Sources

Now answer it yourself.

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