What methods and tools should be used to verify the correctness of REST API?

The following methods and tools are used to verify the correctness of REST API:

• Testing with Postman or Insomnia — convenient GUI tools for manual testing of requests (GET, POST, PUT, DELETE), checking responses, headers, and statuses.
• Automated testing using frameworks — for example, REST-assured (Java), pytest + requests (Python), Supertest (JavaScript). They allow writing tests that verify response correctness, data validation, and error handling.
• Performance testing and load testing — using JMeter, Gatling, k6 to check how the API performs under load.
• Response schema validation — using JSON Schema or OpenAPI specifications to ensure data structure meets expectations.

An example of a simple test in Python using requests and pytest:

import requests

def test_get_user():
    response = requests.get('https://api.example.com/users/1')
    assert response.status_code == 200
    data = response.json()
    assert 'id' in data and data['id'] == 1
    assert 'name' in data

Thus, combining manual and automated testing with status, content, and performance checks provides reliable REST API verification.