What’s the difference between SOAP and REST?

Brief Answer

• SOAP — protocol with formal contracts (WSDL), XML messages, and WS‑* extensions.
• REST — architectural style: resources, HTTP methods, statelessness, caching, clear status codes.
• SOAP fits strict integration and transactions; REST suits web APIs, fast development, and scaling.
• Formats: SOAP is usually XML; REST commonly JSON but supports any media type.
• Transport: SOAP can use multiple transports (HTTP, SMTP, etc.); REST relies on HTTP semantics.

Full Answer

Interaction model

• SOAP — operation‑centric: you call methods (operations) with strict contracts.
• REST — resource‑centric: you work with resources via HTTP (GET/POST/PUT/DELETE).

Contracts and typing

• SOAP uses WSDL/XSD — strict, formal contracts.
• REST is often described with OpenAPI/Swagger — less formal yet sufficient for clients and codegen.

Formats and extensions

• SOAP: XML envelopes, WS‑Security, WS‑ReliableMessaging, transactions.
• REST: flexible formats (JSON, XML, HAL), HTTP caching, ETag, content negotiation.

Errors and statuses

• SOAP: a Fault element with codes/details in XML.
• REST: standard HTTP codes (200, 201, 400, 404, 500) plus an error body.

When to choose

• Choose SOAP: strict compliance, transactional flows, enterprise buses, legacy integration.
• Choose REST: public APIs, microservices, web UIs, faster iteration.

Mini examples

REST:

GET /users/1
Accept: application/json

{"id":1}

SOAP:

<soap:Envelope>
  <soap:Body>
    <GetUser id="1"/>
  </soap:Body>
</soap:Envelope>