Overview
SOAP (Simple Object Access Protocol) and REST (Representational State Transfer) are two approaches to building web services and APIs. Both enable communication between systems, but they differ in protocol, style, flexibility, and use cases. Understanding the differences helps architects choose the right approach for integrations, including Salesforce integrations, enterprise systems, and cloud services.
Key differences
1) Architectural style vs. protocol
SOAP is a protocol with strict standards defined by the W3C. It prescribes an XML-based message structure, rules for data types, and conventions for error handling and security. REST is an architectural style that leverages standard HTTP methods (GET, POST, PUT, DELETE, PATCH). REST doesn’t require a specific message format but commonly uses JSON.
2) Message format
SOAP uses XML exclusively. Messages are wrapped in a SOAP envelope which can include headers and body. REST typically uses JSON today (also supports XML, plain text, HTML, etc.), resulting in smaller payloads and easier parsing in modern web/mobile clients.
3) Transport and operations
SOAP can work over several transport protocols (HTTP, SMTP, TCP). REST primarily uses HTTP and builds APIs around resources accessed via URIs and standard HTTP verbs.
4) Standards and built-in features
SOAP provides built-in standards for security (WS-Security), transactions, reliable messaging, and contracts through WSDL (Web Services Description Language). REST is lighter-weight and does not define standards for these features; they must be implemented using existing web mechanisms (HTTPS, OAuth, custom headers, etc.).
5) Statefulness
SOAP supports stateful operations if needed (via WS-* standards). REST is stateless by principle — each request contains all information needed to process it. Statelessness makes REST easier to scale horizontally.
6) Error handling
SOAP defines a structured fault mechanism (SOAP Fault) in the envelope. REST commonly relies on HTTP status codes (4xx, 5xx) and optional JSON/XML error bodies for additional details.
7) Security
SOAP’s WS-Security supports message-level security (signing and encrypting individual XML elements) and is frequently used in enterprise scenarios. REST usually relies on transport-level security (HTTPS/TLS) and token-based authentication (OAuth 2.0, JWT).
8) Tooling and contract
SOAP’s WSDL provides a strong contract between client and server, enabling automated client code generation. REST can use OpenAPI/Swagger to document endpoints and generate clients, but the contract is more flexible and less prescriptive.
Examples
SOAP request (XML)
Typical SOAP envelope:
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns="http://example.com/service">
<soapenv:Header/>
<soapenv:Body>
<ns:CreateAccount>
<ns:name>Acme Corp</ns:name>
</ns:CreateAccount>
</soapenv:Body>
</soapenv:Envelope>
REST request (JSON, curl)
Typical REST call to create a resource:
curl -X POST https://api.example.com/accounts \
-H "Content-Type: application/json" \
-H "Authorization: Bearer <token>" \
-d '{"name":"Acme Corp"}'
When to choose SOAP vs REST
Choose SOAP if:
– You need strict contracts and formal WSDL-driven tooling.
– You require advanced WS-* features (message-level security, reliable messaging, transactions).
– The environment is enterprise-focused with legacy systems that expect SOAP (many ERP/Banking systems).
Choose REST if:
– You want a lightweight, fast API for web and mobile clients.
– You prefer JSON payloads and easy consumption in JavaScript and modern languages.
– You need scalable, cache-friendly, stateless services and faster iteration.
Best practices for integrations (Salesforce context)
– For Salesforce integrations, use SOAP API when you need full schema/WSDL support or advanced enterprise features. Use REST API (including RESTful composite APIs) for lightweight interactions, mobile apps, web integrations, or when working with JSON-based middleware.
– Secure all endpoints with HTTPS and apply proper authentication (Oauth 2.0 for REST; WS-Security or OAuth for SOAP as applicable).
– Use API versioning and thorough documentation (OpenAPI for REST, WSDL for SOAP).
– Monitor and throttle requests; implement retries with exponential backoff on transient failures.
Conclusion
SOAP and REST solve similar problems but with different philosophies. SOAP provides a feature-rich, standards-driven protocol ideal for enterprise scenarios requiring strict contracts and advanced capabilities. REST offers a simpler, more flexible approach that fits modern web and mobile architectures. Choose based on your project’s security, transactional, interoperability, and performance requirements.