What is a REST API?

A REST API is a way for different applications to communicate with each other over the internet using HTTP.

For example, a frontend application can communicate with a FastAPI backend through REST APIs to:

• Get user information
• Create an account
• Update a profile
• Delete a post

REST APIs mainly use different HTTP methods to tell the server what action should be performed.

Main REST API Methods

The most commonly used HTTP methods are:

1. GET

GET is used to retrieve or read data from the server.

Example:

GET /users

The server might return:

[
    {"id": 1, "name": "Charan"},
    {"id": 2, "name": "Rahul"}
]

Important point

GET should normally not change data on the server.

2. POST

POST is used to create new data.

Example:

POST /users

Request body:

{
    "name": "Charan",
    "email": "[email protected]"
}

The server creates the new user and may return:

{
    "id": 3,
    "name": "Charan",
    "email": "[email protected]"
}

Simple idea

POST = Create something new.

3. PUT

PUT is generally used to replace an existing resource completely.

Example:

PUT /users/3

Request:

{
    "name": "Charan Kumar",
    "email": "[email protected]"
}

The server replaces the existing user information with the supplied representation.

Simple idea

PUT = Replace the resource.

4. PATCH

PATCH is used when you want to partially update a resource.

For example, if you only want to change the email:

PATCH /users/3

Request:

{
    "email": "[email protected]"
}

Other user information remains unchanged.

Simple idea

PATCH = Change only what is needed.

5. DELETE

DELETE is used to remove a resource.

Example:

DELETE /users/3

The server removes the user with ID 3.

Simple idea

DELETE = Remove something.

REST API Methods in FastAPI

FastAPI provides decorators for these HTTP methods:

from fastapi import FastAPI

app = FastAPI()

@app.get("/users")
def get_users():
    return {"message": "Get users"}

@app.post("/users")
def create_user():
    return {"message": "User created"}

@app.put("/users/{id}")
def update_user(id: int):
    return {"message": "User replaced"}

@app.patch("/users/{id}")
def update_partially(id: int):
    return {"message": "User partially updated"}

@app.delete("/users/{id}")
def delete_user(id: int):
    return {"message": "User deleted"}

CRUD and REST Methods

REST methods are closely related to CRUD operations:

GET → Give me data
POST → Create data
PUT → Replace data
PATCH → Change part of data
DELETE → Remove data