Basics of Postman

What is Postman?

Postman is a tool for testing and working with APIs.

You can use it to:

• Send HTTP requests
• Inspect responses
• Test API endpoints
• Add headers and authentication
• Send JSON data
• Save requests into collections
• Write automated API tests

1. HTTP Request Basics

An API request usually has:

METHOD URL

Common HTTP methods:

Example:

GET https://api.example.com/users

2. Creating a Request

In Postman:

1. Create a new request.
2. Select the HTTP method.
3. Enter the URL.
4. Add headers, parameters, or a body if needed.
5. Click Send.

Example:

GET http://localhost:3000/users

3. Query Parameters

Query parameters are added to the URL:

GET /users?page=2&limit=10

In Postman, use the Params tab:

Key      Value
page     2
limit    10

Postman generates:

? page=2&limit=10

without the space:

?page=2&limit=10

4. Headers

Headers provide additional information about the request.

Example:

Content-Type: application/json
Authorization: Bearer TOKEN

In Postman:

Headers
┌─────────────────┬──────────────────┐
│ Key             │ Value            │
├─────────────────┼──────────────────┤
│ Content-Type    │ application/json │
│ Authorization   │ Bearer TOKEN      │
└─────────────────┴──────────────────┘

Common headers:

Content-Type
Accept
Authorization
User-Agent

5. Request Body

POST, PUT, and PATCH requests often send data.

Example JSON:

{
  "name": "Marvin",
  "age": 25
}

In Postman:

Body
  → raw
  → JSON

Then enter the JSON.

Usually you also need:

Content-Type: application/json

6. Reading the Response

After clicking Send, Postman shows the response.

Example:

HTTP/1.1 200 OK

{
  "id": 1,
  "name": "Marvin"
}

Important response information:

• Status code
• Response body
• Response headers
• Response time
• Response size

7. Important Status Codes

200 OK
201 Created
204 No Content

400 Bad Request
401 Unauthorized
403 Forbidden
404 Not Found
409 Conflict

500 Internal Server Error

Think:

2xx → success
4xx → client/request problem
5xx → server problem

8. POST Example

Suppose your API has:

POST http://localhost:3000/users

Body:

{
  "name": "Marvin",
  "email": "marvin@example.com"
}

The server might respond:

201 Created

{
  "id": 42,
  "name": "Marvin",
  "email": "marvin@example.com"
}

9. Authentication

APIs commonly require authentication.

For example:

Authorization: Bearer abc123

Postman has an Authorization tab where you can select authentication types such as:

Bearer Token
Basic Auth
API Key
OAuth 2.0

For a bearer token, Postman generates:

Authorization: Bearer YOUR_TOKEN

10. Collections

A collection is a group of saved requests.

Example:

My API
├── Users
│   ├── Get Users
│   ├── Get User
│   ├── Create User
│   └── Delete User
│
└── Auth
    ├── Login
    └── Logout

Collections are useful for organizing and repeatedly testing an API.

11. Variables

Postman variables let you avoid repeating values.

Instead of:

http://localhost:3000

use:

{{baseUrl}}

Set:

baseUrl = http://localhost:3000

Then:

GET {{baseUrl}}/users

This makes it easy to switch environments:

Development:
http://localhost:3000

Production:
https://api.example.com

12. Environments

An environment is a collection of variables.

Example:

Development
    baseUrl = http://localhost:3000
    token = dev-token

Production
    baseUrl = https://api.example.com
    token = production-token

Then requests can use:

{{baseUrl}}/users

13. Cookies

APIs can use cookies for sessions.

Example:

Cookie: session=abc123

Postman has a cookie manager where you can inspect and manage cookies.

This is useful when testing APIs that use browser-style sessions.

14. Testing Responses

Postman can run JavaScript tests against responses.

Example:

pm.test("Status is 200", function () {
  pm.response.to.have.status(200);
});

Check JSON:

pm.test("Response has a name", function () {
  const data = pm.response.json();

  pm.expect(data).to.have.property("name");
});

15. Typical API Workflow

When developing a backend:

Build endpoint
     ↓
Start server
     ↓
Open Postman
     ↓
Create request
     ↓
Send request
     ↓
Inspect response
     ↓
Fix backend
     ↓
Send again

Example:

POST /users

Send:

{
  "name": "Alice"
}

Check:

Status: 201

Check response:

{
  "id": 1,
  "name": "Alice"
}

16. Postman vs Browser

A browser is mainly designed to display web pages.

Postman is designed to work with APIs.

Browser:

GET /users
        ↓
HTML page
        ↓
Rendered UI

Postman:

GET /users
        ↓
HTTP response
        ↓
JSON

Postman also makes it much easier to:

• Send POST requests
• Set custom headers
• Send JSON bodies
• Test authentication
• Save requests
• Run API tests

17. Postman vs curl

The same request can often be made with either tool.

Postman:

GET http://localhost:3000/users

curl:

curl http://localhost:3000/users

Postman provides a graphical interface.

curl is a command-line tool.

Both ultimately send HTTP requests.

18. Basic Things to Learn First

Focus on these first:

HTTP methods
     ↓
URLs
     ↓
Query parameters
     ↓
Headers
     ↓
JSON bodies
     ↓
Status codes
     ↓
Authentication
     ↓
Variables
     ↓
Collections
     ↓
Tests

These are the core Postman concepts you’ll use when developing and testing backend APIs.