Postman Tutorial: How to Use Postman for API Testing (with Examples)

This guide aims to equip developers & quality assurance (QA) teams with the knowledge and tools needed to efficiently test APIs using Postman, a popular API development environment. Let’s unpack some of these terms before diving in.

What is Postman?

Postman is a popular API platform and development tool that allows users to design, test and document APIs efficiently. It provides a user-friendly interface for sending HTTP requests, receiving responses, automating tests and managing API endpoints, enabling developers to streamline API development and testing workflows.

What API testing?

API testing involves evaluating APIs to ensure they function correctly, perform under load, and are secure and reliable. During testing, requests are sent to the API endpoints, and responses are analyzed to ensure they meet expected outcomes.

In this guide, we’ll demonstrate how to use Postman to test various endpoints in CoinGecko API. Specifically, we’ll run through live examples covering these endpoints:

1. Coin Price by Ids – /simple/price
2. Top Gainers and Losers – /coins/top_gainers_losers **requires a Pro API key (paid subscribers only)
3. Coins List with Market Data – /coins/markets
4. Coin Data by ID – /coins/{id}

With that, let’s get started!

Prerequisites

To follow along, be sure to have the following installed and available: 

• CoinGecko API: We will use the CoinGecko API to fetch market data for cryptocurrencies. The free Demo plan is sufficient in the context of ths guide, for most of the examples shown unless otherwise stated. Create a Demo account to get your complimentary API key, capped at 10,000 calls per month and a rate limit of 30 calls per minute.
• Postman API Platform: Ensure the Postman app is installed on your device to continue with this guide.

Step 1: Open Postman & Create a New Collection to Store Requests

Open the Postman app and create a new collection under the Collections section to store your CoinGecko API requests. Consider giving the collection a meaningful name.

Now your screen should look similar to this:

Step 2: Authorize the API with an API Key

For APIs with keyed authentication, every request needs to be authorized. In the case for CoinGecko API, it needs to be authorized either by passing the API key in the header or as query parameters. For this walkthrough, we will add the CoinGecko API key to the header of each request.

Since we have multiple API endpoints to test, copying and pasting the API key into the headers of each request can be tedious. To simplify this, we will use Postman’s Header Presets to add the API key once and use it whenever needed.

To do this, create a new request and add the API key as a headers preset. Click on the donut menu (the three vertical dots) of the collection you created initially and select 'Add Request'. This will display a request boilerplate screen.

Next, navigate to the 'Headers' tab – you’ll see the headers section for the request. At the end of this section, you'll find a 'Presets' dropdown. Click on it and then select 'Manage Presets'. A 'Manage Header Presets' popup will appear.

In this popup, click on 'Add Header Preset'. You’ll be asked to provide a name for the preset. Under the 'Key' column, enter 'x-cg-pro-api-key', and in the 'Value' column, enter the API key generated earlier. Finally, click the 'Add' button.

Now, your header preset is created and ready to be used for any request.

Step 3: Enter Requests & Parameters for Specific Endpoints

This section will focus on entering requests and parameters using CoinGecko API endpoints as examples.

Select the HTTP method

Depending on what you want to do with the endpoint, the HTTP request method could be GET (retrieve data from the server), POST (send data to the server for processing), PUT (replace a resource) etc.

Enter the Request URL

Enter the Request URL of the specific endpoint you'd like to test. For example, if you’re trying to get data for a specific cryptocurrency with the /coins/id endpoint, your Request URL will be: https://api.coingecko.com/api/v3/coins/bitcoin.

Enter the Parameters

These are additional pieces of information that you can include in your request to specify or filter the data you’re asking for. Parameters are added to the end of the URL after a question mark ('?'). For example, if you only wanted to get data from the last 24 hours, your URL will appear as: https://api.coingecko.com/api/v3/coins/bitcoin?time_period=24h.

Send the Request

Once you’ve selected the HTTP request method, entered the request URL and specified parameters, you can send the request. The API will return a response accordingly.

Handling the API Response

The API will return data based on your request. You’ll need to handle this data in your application. This could involve parsing the data, error handling, or updating the UI of your application.

Using Postman for API Testing (with Endpoint Examples)

In this section, we'll share how you can use Postman to test various endpoints.

Coin Price By IDs

The /simple-price endpoint allows us to query the live or historical price data for specific cryptocurrencies listed on CoinGecko, by using their unique coin IDs.

You can specify one or multiple coin IDs in your request, and optionally include data points around market cap, 24-hour trading volume, 24-hour price percentage change and more, depending on the parameters of your query.

In Postman, we'll set up our request by choosing the GET method and entering the above endpoint into the URL field.

• HTTP Method: GET
• Request URL: https://api.coingecko.com/api/v3/simple/price
• View query params on our API docs

  Use the header preset as shared in the previous section, to ensure your request is authenticated with the API key.

For this endpoint, there are 2 required parameters and 5 optional parameters, that you can include in the Params section of the Postman request:

After adding required parameters, send the request. The response structure should look like this:

Note: The response may vary according depending on your request parameters.

Top Gainers and Losers

The /coins/top_gainers_losers endpoint allows us to query the top 30 coins with largest price gains and losses within a specific time frame. Please note that this is a paid exclusive endpoint and requires you to be subscribed to a paid plan in order to call the 'pro-api.coingecko.com' root URL.

Similarly, set up your request in Postman:

• HTTP Method: GET
• Request URL: https://pro-api.coingecko.com/api/v3/coins/top_gainers_losers
• View query params on our API docs

After sending the request, the response structure should appear as follows:

Note: The response may vary according depending on your request parameters.

Coins List with Market Data

The /coins/markets endpoint allows us to fetch real-time crypto price, trading volume over the last 24 hours, its market cap, and other relevant metrics for specific cryptocurrencies. This information is crucial for traders, analysts, and developers who need up-to-date and accurate data to make informed decisions regarding investments, market strategies, or application integrations.

Set up your request in Postman accordingly:

• HTTP Method: GET
• Request URL: https://api.coingecko.com/api/v3/coins/markets
• View query params on our API docs

After sending the request, the response structure should appear as follows:

Note: The response may vary according depending on your request parameters.

Coin Data by ID

Call the /coins/id endpoint in the CoinGecko API to return crypto price, market data, metadata and exchange tickers for a cryptocurrency, as specified by the coin id parameter. This endpoint is useful for obtaining in-depth information about a particular coin, providing insights beyond market performance. When querying the API with a specific coin ID, it returns a dataset that includes:

• Basic information: The coin's name, symbol, and description
• Market data: Current price, market capitalization, 24-hour trading volume, price changes, and more
• Historical data: Historical price data for specified timeframes, which is valuable for trend analysis
• Developer data: Information about the coin's development activity, such as repository statistics and commit history
• Community data: Metrics related to the coin's community engagement, like social media followers and forum activity
• Supply information: Total and circulating supply of the coin
• Additional metadata: Links to the coin's official website, whitepapers, and other relevant resources

Set up your request in Postman accordingly:

• HTTP Method: GET
• Request URL: https://api.coingecko.com/api/v3/coins/{id} – Ensure you replace {id} with a unique coin id like 'bitcoin', 'ethereum', 'solana' etc. For example:
  • To get data for Bitcoin, where id is 'bitcoin', the Request URL is: https://api.coingecko.com/api/v3/coins/bitcoin
  • To get data for Ethereum, where id is 'ethereum', the Request URL is: https://api.coingecko.com/api/v3/coins/ethereum
• View query params on our API docs

After adding the required parameters and sending the request, the response structure will be an array of objects appearing as such (for the 'bitcoin' id):

Conclusion

We've provided a comprehensive walkthrough on how to easily test APIs using Postman, with live examples using specific CoinGecko API endpoints. It covers the prerequisites, setting up Postman, authorizing the API with a key, and making requests to various endpoints.

By following this guide, developers, traders, and analysts can gain reliable access to the most recent market data offered by CoinGecko. Those looking to make the most of the comprehensive range of cryptocurrency data provided by CoinGecko API can find out more below!