SOAP, REST, GraphQL and gRPC compared

The same job, four ways

An API lets one program ask another to do something. The main styles differ in format, contract and how the client asks for data.

	SOAP	REST	GraphQL	gRPC
Format	XML envelopes	JSON (usually) over HTTP	JSON over HTTP, one endpoint	Binary Protocol Buffers over HTTP/2
Contract	WSDL, very formal	OpenAPI (optional)	A typed schema	A .proto schema, required
Client asks by	Calling named operations	Resource URLs and HTTP verbs	Sending a query describing the fields wanted	Calling typed methods
Caching	Hard	Natural (HTTP caching)	Harder (usually one POST endpoint)	Not HTTP-cache friendly
Streaming	No	Limited (SSE, WebSockets separately)	Subscriptions	Built in (four modes)
Browser use	Possible, heavy	Native	Native	Needs a proxy (gRPC-Web)
Typical home	Banks, enterprise, older systems	Public and general-purpose APIs	Client-driven apps, mobile	Internal service-to-service

SOAP

An older, XML-based protocol with a formal contract (WSDL) and a family of standards (WS-Security, transactions, reliable messaging). Verbose and tooling-heavy, but still common where strict contracts and built-in enterprise standards matter, such as banking, telecom and government. You will mostly meet it when integrating with existing systems.

REST

Design around resources identified by URLs (/orders/42), manipulated with standard HTTP verbs (GET, POST, PUT/PATCH, DELETE), and described with status codes. Strengths: simple, cacheable, works with every tool. Weaknesses: over-fetching (you get fields you do not need), under-fetching (several calls to assemble a screen), and no enforced schema unless you add one.

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Figure SDA-CORE-20-1 · Three ways to call an API · © forcsguy.com

GraphQL

A single endpoint and a typed schema. The client sends a query naming exactly the fields it wants, even across related objects, and receives exactly that shape. It removes over- and under-fetching and suits varied clients (web, mobile). Costs: query cost control (a client can ask for something expensive), more complex caching, and server complexity (resolvers, the N+1 problem solved with batching).

gRPC (a form of RPC)

Remote procedure call: call a method on another service as if it were local. gRPC uses Protocol Buffers (compact binary, generated typed clients in many languages) over HTTP/2 with streaming. It is fast and has strong contracts, which is why it is popular between internal services. It is awkward to call straight from a browser and harder to debug by eye.

Choosing

1. Who are the clients? Public developers and the broad ecosystem: REST. A few first-party apps with varied screens: GraphQL. Your own services: gRPC. A partner or legacy system: whatever they provide, often SOAP.
2. How sensitive is performance and payload size? Internal high-volume calls favour gRPC.
3. Do you need HTTP caching? REST makes it easy.
4. Do you need streaming? gRPC, or WebSockets and server-sent events.
5. Team skills and tooling: the best style is one your team can run well.

Many systems mix styles: REST publicly, gRPC internally, and GraphQL as a gateway layer over both.

Good habits in any style

• Version the API and avoid breaking changes.
• Use consistent errors and clear status codes.
• Paginate lists, and make unsafe operations idempotent with keys.
• Document with a machine-readable schema (OpenAPI, GraphQL SDL, .proto).
• Apply authentication, authorisation and rate limits at the edge (see the API security lesson).

Real-world reading