You’ve built the frontend, set up the backend, and connected the endpoints—or so you think. Then someone suggests, “Test it in Postman.” If you’re new to APIs, you might feel lost and think, “What now?” Let’s clear that up.
Whether you’re a developer debugging your endpoints, a product manager verifying API responses, or a startup founder trying to keep up, Postman and similar tools can help bridge the gap between your ideas and their execution.
In this guide, you’ll learn what Postman is, why it’s useful, and how to use it to confidently test a REST API (Representational State Transfer Application Programming Interface) even if you’ve never written a single line of backend code.
What Is Postman and Why Do Developers Rely on It?
Postman is an API platform used for testing, documenting, and collaborating on REST APIs. You can think of it as your API control room, where you can:
- Send HTTP requests to an API
- View the exact response from the server
- Modify your inputs, headers, tokens, and parameters to debug responses
- Save your test calls, create collections, and automate tests
Before Postman, developers had to write curl commands in the terminal or build quick frontend user interfaces to test endpoints. Postman changed this process by consolidating all the necessary features into one visual and accessible platform.
Why Should You Test an API in the First Place?
Imagine you’re building a to-do list app that’s connected to your backend. However, you encounter several issues:
- New tasks aren’t saving.
- Completed tasks don’t disappear.
- Your app is displaying a blank screen.
What’s causing these problems? Is it a fault in the frontend, or is the API returning incorrect data? This is where Postman becomes invaluable. Instead of making guesses, you can call the API directly and see exactly what it returns in raw JSON format, without needing to involve the frontend.
Step-by-Step: How to Use Postman to Test a REST API
Let’s go through a real-world scenario. Imagine you want to retrieve a list of users from a public API such as:
https://jsonplaceholder.typicode.com/users
Here’s how to test it in Postman:
Step 1: Download & Launch Postman
Visit https://postman.com to download the app. If you prefer, you can also use the web version.
Step 2: Create a New Request
Click the “+” button to open a new request tab. In the dropdown menu, select GET (this is the default method). Then, paste the URL:
https://jsonplaceholder.typicode.com/users
Step 3: Send the Request
Click the orange “Send” button. Wait for a moment. You’ll receive a JSON response like this:
[
{
"id": 1,
"name": "Leanne Graham",
"email": "leanne@example.com"
},
...
]
This indicates that the API is functioning properly by returning a list of users from the server.
Step 4: Explore the Response Tabs
Postman organises the response into several tabs:
- Body: The actual data (in JSON/XML/etc.)
- Headers: Metadata about the response (e.g. content-type, cache-control)
- Status: The HTTP status code (
200 OK,404 Not Found, etc.) - Time: The duration it took to receive the response
This is the place where debugging becomes essential.
Step 5: Modify the Request
Experiment by changing the method to POST, PUT, or DELETE if the API supports those options. You can also:
- Add query parameters (e.g.
?limit=10) - Include headers (e.g.
Authorization: Bearer <token>) - Add a request body in JSON format
Each adjustment allows you to simulate how your application interacts with the API.
Bonus: Testing Secured APIs with Auth Tokens
Most APIs are not open and require authentication. This can be done using:
- API keys
- Bearer tokens
- OAuth2 workflows
Postman makes managing this authentication easy through its Authorisation tab. Once you have your credentials from your developer or API provider, you can test authenticated routes, such as /users/me or /admin/dashboard, without encountering “401 Unauthorised” errors.
Why This Matters Even If You’re Not a Developer
If you’re part of a product team, testing APIs in Postman offers several benefits:
- Verify product behaviour before launch
- Create better, more accurate API documentation
- Troubleshoot issues without needing engineering to pause their work
- Understand how your app communicates with the backend and identify where breakdowns occur
In other words, you enhance your value to your team.
TL;DR — Postman Makes the Invisible Visible
You don’t need to write code to understand APIs. You don’t have to be a backend engineer to identify a broken endpoint. All you need is a tool like Postman and a bit of curiosity.
Testing an API isn’t just about finding mistakes; it’s about grasping how the system works. In a product-driven world, understanding is what truly matters.
If you’re new to APIs or trying to understand how they work, check out our guide titled “What Is an API and Why Do Developers Love Them?” This guide explains what APIs are, how they drive the internet, and why they have become essential tools for developers.
