What is the difference between SOAP and REST?

Two main approaches to building web services.

Characteristic	SOAP	REST
Protocol	Based on XML, operates over HTTP, SMTP, TCP, and other protocols.	Based on HTTP, uses existing HTTP methods (GET, POST, PUT, DELETE).
State	State transfer is explicitly conveyed in messages.	The service does not store client state. State is transferred in each request.
Data formats	Strictly defined XML format (SOAP envelope).	Can use various formats: JSON, XML, Plain Text, HTML. JSON is the most common.
Architectural style	Protocol with strict rules.	Set of architectural principles.
Caching	No built-in caching support.	Uses HTTP standards for caching (Cache-Control headers).
Performance	Often slower due to XML parsing and protocol overhead.	Usually faster and lighter thanks to JSON simplicity and HTTP methods.
Security	WS-Security provides comprehensive mechanisms.	Depends on basic HTTP/HTTPS mechanisms and tokens (OAuth, JWT).
Contract	WSDL (Web Services Description Language) strictly describes operations and data formats.	Usually no formal contract, often uses OpenAPI (Swagger) for documentation.
Complexity	More complex to implement and consume.	Simpler to implement and consume.

SOAP is suitable for enterprise systems requiring high reliability, strict typing, and transactional support. REST is preferred for web applications, mobile development, and microservices due to its lightweight and flexible nature.