Overview
SOAP and REST are two widely used approaches for building web services. While both enable communication between systems, they differ in architecture, message formats, standards, and typical use-cases. Understanding the differences is essential for Salesforce developers working with integrations — e.g., choosing between Salesforce SOAP API and Salesforce REST API.
Architectural Style
SOAP (Simple Object Access Protocol) is a protocol with a strict standard and built-in rules for message structure, error handling, and security (WS-* standards). REST (Representational State Transfer) is an architectural style that leverages standard HTTP methods and focuses on resources and stateless interactions.
Protocol vs Style
SOAP defines a formal contract (WSDL) and uses XML for messages. REST is architectural — it can use multiple formats (JSON, XML, plain text), and typically uses JSON for web APIs today.
Message Format & Transport
SOAP messages are always XML envelopes. SOAP can be transported over various lower-level protocols (HTTP, SMTP, TCP). REST primarily uses HTTP/HTTPS and leverages HTTP verbs: GET, POST, PUT, PATCH, DELETE.
Security
SOAP supports WS-Security (message-level security), which provides features like XML Encryption, XML Signatures, and more fine-grained policies. REST typically relies on transport-level security (TLS/HTTPS) and token-based schemes (OAuth 2.0, JWT). For enterprise integrations requiring message-level confidentiality and complex security policies, SOAP is common; for modern web/mobile apps, REST + OAuth is most used.
Standards, Contracts & Tooling
SOAP exposes a WSDL (Web Services Description Language) that describes operations, messages, and bindings — enabling strong type contracts and auto-generated client code. REST has no single contract standard; APIs may provide OpenAPI/Swagger specifications, but these are optional. In Salesforce context, SOAP API provides WSDL for generating client stubs, while REST API is documented via REST resources and OpenAPI in some cases.
Caching & Performance
RESTful GET responses can be easily cached (HTTP caching headers), improving performance for read-heavy operations. SOAP uses POST-like operations wrapped in XML and is less cache-friendly. REST with lightweight JSON payloads is generally faster and more efficient over mobile and web compared to verbose SOAP XML.
Error Handling
SOAP has a structured fault element inside the SOAP envelope for errors. REST commonly uses HTTP status codes (4xx, 5xx) and error payloads (often JSON) to convey failure details.
When to Use Which?
Use SOAP when you need:
- Formal contracts (WSDL) and strict typing.
- Advanced security (WS-Security, message-level).
- Transactional reliability or built-in WS-* features.
Use REST when you need:
- Lightweight, fast APIs for web and mobile (JSON).
- Simple CRUD operations using HTTP verbs with caching.
- Flexible, easy-to-consume endpoints for modern apps.
Quick Examples
SOAP request (simplified):
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:urn="urn:partner.soap.sforce.com">
<soapenv:Body>
<urn:login>
<urn:username>[email protected]</urn:username>
<urn:password>passwordTOKEN</urn:password>
</urn:login>
</soapenv:Body>
</soapenv:Envelope>
REST request (curl):
curl -X POST \
-H "Content-Type: application/json" \
-d '{"Name":"Acme","Phone":"1234567890"}' \
https://yourInstance.salesforce.com/services/data/vXX.X/sobjects/Account/
Summary
In short: SOAP is a heavyweight, standardized protocol with strong contracts and advanced security; REST is a lightweight architectural style built on HTTP, optimized for simplicity, performance, and modern app development. As a Salesforce developer, choose SOAP when you require WSDL-driven contracts or WS-* features; choose REST for most web/mobile integrations where speed and ease-of-use matter.
Keywords: SOAP vs REST, difference between SOAP and REST, Salesforce SOAP API, Salesforce REST API, web services comparison