Postman Guide

2 min read

Postman Intro Guide

Quick Guide to Write & Test APIs with Postman

Background Knowledge

Understand APIs & HTTP basics

Why Use Postman?

Test backend without a frontend

Write Backend Code

Define API routes in VS Code

Test APIs

Send requests and inspect responses

VS Code vs Postman

Where to find info

Status Code	Meaning	When to Expect
200 OK	Request succeeded	Successful GET, POST, PUT, PATCH, DELETE
201 Created	Resource created	Successful POST that creates a resource
204 No Content	Request succeeded, no response body	Successful DELETE or PUT with no response content
400 Bad Request	Malformed request syntax or invalid data	When request JSON or parameters are invalid
401 Unauthorized	Authentication required or failed	Missing or invalid auth token/cookie
403 Forbidden	Authenticated but not allowed	Access denied for user to resource
404 Not Found	Resource not found	Invalid endpoint or missing resource
500 Internal Server Error	Server encountered an error	Unhandled exceptions or errors on backend

Method	Purpose	Usage in VS Code	Postman Tip
GET	Retrieve data	Route with `methods=['GET']`	No body needed
POST	Create data	Read JSON from request body	Use Body tab to send JSON
PUT	Replace data	Replace full record	Send full updated data
PATCH	Update part	Partial update logic	Send partial JSON data
DELETE	Remove data	Delete from database	No body needed

Test backend code (in python flask, java spring, etc.) without having a functional frontend . This allows for students to work on and test different pieces of the project seperately before joining them together. .
Allows for quick debugging of APIs + Test Cookie/Token storage that may be generated by the backend (typically for authorization).
Has its own collaboration system such as shared workspaces and collections where team members can share postman requests.

Pro Coder Tip: For more info on any tool (in this case postman) visit its offical documentation Postman Docs

1. Create API endpoints in an api file (flask framework) + define in main.py
2. Use the terminal in VS Code to run your Flask localhost server (python main.py).

Choose method (GET, POST, etc.) and enter your API URL (which consists of your endpoint from your code + local host server from python main.py.

Backend (VS Code)	Testing (Postman)
localhost url + endpoint	type localhost url + endpoint into send bar

Find API call method	Select HTTP method and enter URL, click Send

Use `request.json` to read JSON data	Enter JSON data under Body → raw → JSON

Handle cookies with `request.cookies`	Manage cookies in Postman’s Cookies tab