REST vs. RPC: Understanding the Core Differences in API Design

When it comes to designing web APIs, two common architectural styles often spark debate: REST and RPC. Both use HTTP as a transport layer, but they follow distinct philosophies. Let’s dive deeper to understand what sets them apart, when to use each, and why the underlying transport (like HTTP) doesn't make them the same thing.

🔹 REST: Resource-Oriented

REST (Representational State Transfer) is an architectural style that revolves around resources — entities that can be created, retrieved, updated, or deleted. Each resource has a unique URL, and you use standard HTTP methods like GET, POST, PUT, and DELETE to interact with them.

For example, if you’re managing users:

• GET /users/123 retrieves user with ID 123.
• POST /users creates a new user.
• PUT /users/123 updates the user’s details.
• DELETE /users/123 removes the user.

REST embraces HTTP semantics. It leverages status codes, headers, and even caching mechanisms. It encourages a uniform interface, making APIs more predictable and discoverable.

🔸 Key traits of REST:

• Strong alignment with HTTP protocol.
• Emphasis on resources (nouns).
• Stateless interactions (each request contains all necessary context).
• Ideal for CRUD-based systems (Create, Read, Update, Delete).

🔸 RPC: Action-Oriented

RPC (Remote Procedure Call), by contrast, is about invoking methods on a remote server, much like calling a function in your local codebase. Instead of focusing on resources, RPC focuses on actions or procedures.

For instance:

• POST /getUserById with { "id": 123 } as payload.
• POST /processPayment with details of the payment.

In RPC, the URL represents a verb (like processPayment or syncData), not a noun. The HTTP method (often just POST) acts as a simple wrapper to send the request — the semantic weight of HTTP is largely ignored.

🔸 Key traits of RPC:

• Emphasis on actions (verbs) rather than resources.
• Often uses custom endpoints (like /doSomething).
• HTTP is treated as a mere transport layer, not part of the contract.
• Common in microservices or internal APIs where speed and flexibility are key.

🔍 Can RPC Use HTTP or REST as Its Underlying Layer?

Here’s where confusion often arises. Yes, RPC can use HTTP as its underlying transport. You can design RPC-style APIs over HTTP/1.1 or HTTP/2, sending JSON or even binary data. However, this doesn’t make it RESTful.

The key distinction is that REST leverages the semantics of HTTP itself:

• REST uses HTTP methods to mean something: GET is safe and idempotent, POST creates, DELETE removes.
• REST uses HTTP status codes (like 200, 404, 500) to communicate success or errors.
• REST APIs are typically stateless and designed for easy caching, scaling, and discoverability.

In contrast, RPC over HTTP (like JSON-RPC, XML-RPC, or custom JSON APIs) simply uses HTTP as a tunnel. The server is essentially a black box that executes requested methods, with little regard for HTTP semantics.

A modern example is gRPC, which runs on HTTP/2 and uses Protocol Buffers. It’s blazing fast and compact, but it doesn’t follow REST principles.

🆚 Key Differences at a Glance

💡 Additional Considerations

• Complex Operations: If you need to model complex business workflows that don’t map cleanly to CRUD, RPC might be a better fit. For example, generateMonthlyReport doesn’t align neatly with a RESTful noun.
• Coupling: RPC-style APIs often result in tight coupling between client and server, since the method signatures are predefined and more rigid.
• Developer Experience: REST APIs tend to be more discoverable and easier for third-party developers to understand and integrate with, especially when well-documented.
• Performance: gRPC (a modern RPC framework) can significantly outperform REST APIs, especially for internal, high-frequency communication between services.

🔚 Finally

While REST and RPC might both use HTTP as the transport layer, they represent fundamentally different approaches to API design:

• REST leans into HTTP’s native semantics, focusing on resources and stateless interactions, perfect for public-facing APIs and web applications.
• RPC focuses on procedural operations, giving you the flexibility to model actions and workflows, often preferred for internal services and microservice architectures.

Understanding these differences helps you choose the right approach based on your system’s requirements, developer experience, and performance needs.

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