gRPC vs REST: Which to Choose (and What It Costs)

Mariana Berga, André Santos · Imaginary Cloud ·

6 min read Original article ↗

gRPC and REST: comparison

Now that we have the overview, here is where the two genuinely diverge.

HTTP/1.1 vs HTTP/2

REST APIs follow a request-response model, most commonly built on HTTP/1.1. If a service receives multiple requests from multiple clients, it handles them one at a time and the whole system slows down behind the queue. REST can be served over HTTP/2, but the request-response model stays the same, which stops it from making the most of what HTTP/2 offers.

gRPC is built on HTTP/2 and can take multiple requests from several clients and handle them simultaneously, streaming information continuously. It handles unary interactions too — a single request answered by a single response, which is how every REST call works.

So gRPC covers unary interactions and three kinds of streaming:

  • Unary: the client sends a single request and receives a single response.
  • Server-streaming: the server responds with a stream of messages to a client's request, then sends a status message to close the process.
  • Client-streaming: the client sends a stream of messages and receives a single response back.
  • Bidirectional-streaming: the two streams are independent, so both sides can transmit in any order. The client initiates and ends the exchange.

Types of Streaming gRPC vs REST

Browser support for gRPC and REST

This is REST's single biggest advantage. REST is supported by every browser. gRPC is not: it needs gRPC-Web plus a proxy layer to translate between HTTP/1.1 and HTTP/2, which is why gRPC tends to live in internal and private systems.

That proxy is not a footnote. It is a component your team installs, configures, monitors and pays to run, sitting on the path of every browser request. Envoy is the default, and it has a dedicated gRPC-Web filter to do the job.

There is a second catch that most comparisons omit. gRPC-Web does not support client-side or bidirectional streaming — server streaming only. So the moment a browser is involved, the streaming advantage that gets quoted most often in gRPC's favour is half gone.

Payload data structure: Protobuf vs JSON

gRPC uses Protocol Buffers by default to serialise payload data. It is lighter, because the format is compact and the messages come out smaller. Protobuf is binary, and those strongly typed messages convert automatically into whichever language the client and server are written in.

REST mostly relies on JSON or XML. REST does not mandate any structure, and JSON won on flexibility: it will carry dynamic data without insisting on a strict shape. It is also readable by a human being, which Protobuf is not. Think of JSON as a parcel with the contents written on the outside in plain handwriting, and Protobuf as the same parcel with a barcode. One you can read at a glance. The other the machine reads instantly, and you need a scanner.

That readability has a price. JSON is not as light or as fast in transmission, because it must be serialised and converted into the language used on both sides. An extra step in the journey, and one more place for things to go wrong.

The same booking lookup, both ways

REST — a resource, and a shape you infer from the response:

GET /api/v1/bookings/8f2c1e HTTP/1.1
Host: api.example.com
Accept: application/json
{
  "id": "8f2c1e",
  "guestName": "A. Fernandes",
  "roomType": "double",
  "checkIn": "2026-08-14",
  "nights": 3,
  "totalCents": 42000,
  "currency": "EUR"
}

Nothing stops a service adding discountCents next Tuesday, and nothing stops a client quietly ignoring the fact that totalCents now means something slightly different.

gRPC — the contract is a file, and it exists before either side is written:

syntax = "proto3";

package booking.v1;

service BookingService {
  rpc GetBooking (GetBookingRequest) returns (Booking);
  rpc WatchAvailability (AvailabilityRequest) returns (stream AvailabilityUpdate);
}

message GetBookingRequest {
  string booking_id = 1;
}

message Booking {
  string   booking_id = 1;
  string   guest_name = 2;
  RoomType room_type  = 3;
  string   check_in   = 4;  // ISO-8601 date
  uint32   nights     = 5;
  Money    total      = 6;

  // field 7 was `total_cents`, removed in v1.4 — never reuse the number
  reserved 7;
  reserved "total_cents";
}

enum RoomType {
  ROOM_TYPE_UNSPECIFIED = 0;
  ROOM_TYPE_SINGLE      = 1;
  ROOM_TYPE_DOUBLE      = 2;
}

Two lines there do work the REST version cannot. stream on WatchAvailability declares the streaming case in the contract rather than bolting it on with polling or a websocket. And reserved 7 is the versioning argument in miniature: that field number can never be reused, so a client compiled against the old schema cannot silently misread the new one. The compiler enforces what REST leaves to a convention someone has to remember.

The cost is visible in the same snippet. That file has to be compiled, versioned and distributed to every consumer before anyone can make a single call — and none of it is readable in a browser tab.

Code generation in gRPC and REST

REST APIs have no built-in code generation. Developers reach for a third-party tool such as Swagger or Postman to produce request code, or work from the framework they already use.

gRPC generates code natively through its protoc compiler, which supports a wide range of languages. That matters most in systems where services are written in different languages on different platforms. The same generator also makes building an SDK considerably less painful.

Security in gRPC and REST

Both run over TLS, so neither is inherently more secure at the transport layer, and gRPC has built-in support for TLS and token-based authentication. The difference is everything around them. REST inherits the entire HTTP security estate: API gateways, web application firewalls, OAuth flows and rate limiters all understand it out of the box.

gRPC needs tooling that speaks HTTP/2 and Protobuf to do the same job. Gateway support exists, but the field is narrower. And an inspection layer that cannot read a binary payload cannot enforce a rule about what is inside it.

Error handling and status codes

REST leans on HTTP status codes, which every client library, log aggregator and monitoring tool already speaks. A 404 means the same thing everywhere.

gRPC defines its own status codes, such as NOT_FOUND and DEADLINE_EXCEEDED. They are richer for service-to-service calls, and they sit outside the HTTP vocabulary your existing tooling grew up with. Adopting gRPC means teaching your monitoring stack a second language for failure.

Versioning and schema evolution

This is where a contract-first approach earns its keep. Protobuf identifies fields by number rather than by name, so adding a field is backwards compatible by design and older clients quietly ignore what they do not recognise. The schema is the contract, and the compiler checks it.

REST offers no equivalent guarantee. Compatibility rests on discipline: versioned URLs, clients written to ignore fields they do not know, and a convention everyone remembers to follow. It works. Nothing enforces it.

Debugging and observability

A REST call can be inspected with curl, a browser tab or a log line, by anyone, with no preparation at all. A gRPC call cannot. The payload is binary, so you need a tool like grpcurl and the right proto file before you can read it.

That gap never shows up in a benchmark. It shows up on a Friday evening, in how long it takes an on-call engineer to see what a failing request actually contained.