Overview
SOAP and REST are two widely used approaches for building web services. While both enable communication between systems, they differ significantly in architecture, message format, standards, and common use cases. Understanding these differences is essential for choosing the right integration method for Salesforce and other enterprise systems.
Protocol vs. Architectural Style
SOAP (Simple Object Access Protocol) is a protocol with strict standards and built-in rules. REST (Representational State Transfer) is an architectural style that uses standard HTTP methods and is more flexible.
Message Format
SOAP messages are XML-based and wrapped inside a SOAP envelope. REST commonly uses JSON (though it can use XML or other formats), which is usually smaller and easier to parse.
Transport
SOAP is transport-agnostic and can operate over HTTP, SMTP, TCP, etc. In practice, SOAP is most often used over HTTP. REST relies on HTTP/HTTPS and leverages standard HTTP methods (GET, POST, PUT, DELETE, PATCH).
Standards and Contract
SOAP follows formal standards (WSDL for service contract, WS-Security for security, WS-ReliableMessaging, etc.). REST has no formal contract standard; it is defined by URI patterns and HTTP semantics, though OpenAPI (Swagger) is commonly used to describe REST APIs.
Operations vs Resources
SOAP exposes operations (RPC-style) — you call methods defined in the WSDL. REST models everything as resources; you operate on resource representations using HTTP verbs.
Security
SOAP provides built-in security extensions (WS-Security) for message-level security: XML Encryption, XML Signatures, and token-based approaches. REST typically relies on transport-level security (HTTPS/TLS) and common frameworks like OAuth 2.0, JWT, and custom headers for authentication and authorization.
Performance & Caching
REST with JSON is generally lighter-weight and faster due to smaller payloads and direct use of HTTP caching (Cache-Control headers). SOAP messages are heavier because of XML verbosity and envelope overhead.
Error Handling
SOAP uses standardized fault elements within the SOAP envelope. REST uses HTTP status codes (4xx, 5xx) and may return error details in the response body (often JSON).
Transactions & Reliability
SOAP supports advanced features (WS-AtomicTransaction, WS-ReliableMessaging) useful for complex enterprise scenarios requiring guaranteed delivery, transactions, or routing. REST does not define such standards; reliability must be handled at the application layer.
When to Choose SOAP
Use SOAP when you need:
- Formal contract via WSDL
- Built-in WS-* standards (security, transactions, reliable messaging)
- Tight contract-based integrations typical in enterprise systems (banking, telecom)
When to Choose REST
Use REST when you need:
- Lightweight, scalable APIs (public web APIs, mobile backends)
- Simple CRUD-style operations on resources
- Easier consumption by web/mobile clients and better performance with JSON
Example: SOAP Request (XML)
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:urn="urn:examples:helloservice">
<soapenv:Header/>
<soapenv:Body>
<urn:sayHello>
<name>Alice</name>
</urn:sayHello>
</soapenv:Body>
</soapenv:Envelope>
Example: REST Request (curl, JSON)
curl -X POST https://api.example.com/v1/users \
-H "Content-Type: application/json" \
-d '{"name":"Alice","email":"[email protected]"}'
Summary
SOAP and REST solve similar problems but in different ways. SOAP brings strict standards and enterprise-grade features; REST brings simplicity, performance, and ease of use for web-scale APIs. Choose based on functional requirements: contract & reliability vs. performance & simplicity.
Keywords
SOAP vs REST, SOAP web services, RESTful API, WSDL, JSON, XML, HTTP methods, WS-Security, OAuth, integration