What are API Parameters? Technical topics explained simply

What are API Parameters?

Parameters are empty places in memory to store variables or arguments. When building web applications, parameters are a fundamental part of the API design and function. For example, when designing your e-commerce shop, you know you'll need an `itemCost` parameter, a `shippingCost` parameter, and a `location` parameter to calculate the `salesTax` parameter. Any resource that is potentially variable requires a parameter.

Parts of an API Parameter

According to the [Open API 3 specification](https://swagger.io/specification/), to describe a parameter, you specify its name, location, data type (defined by either schema or content), and other attributes, such as description or required. Here is an example of a path parameter:


paths:
  /users/{userId}: # parameter name
    get:
      summary: 
      parameters:
        - in: # location
          name: userId
          schema:
            type: integer # data type
          required: true 
          description: Numeric ID of the user to get

Types of Parameters in API

There are multiple types of parameters:

Path parameters, such as `/users/{id}`. These point to a specific resource. In this case, they're pointing to a specific user's ID number.
Query parameters, such as `/users?role=admin` The query parameter defines sort, pagination, or filter operations. See Query Parameters for more information.
Header parameters, such as `X-MyHeader: Value` Header parameters are most often used in API security and authentication. See API Authentication for more information on using API tokens in your header parameters.
Request body parameters, which look similar to query parameters, are most often used in POST requests to send values in the request body.
Cookie parameters, which are passed in the `Cookie` header, such as `Cookie: debug=0; csrftoken=BUSe35dohU3O1MZvDCU` A cookie is an HTTP request header that contains the cookies previously sent by the server using `set-cookies`.

How do I use Parameters in API?

Parameters house variables, so think of building parameters into your API as similar to declaring a function in C, then passing values to that function. Remember, there are different kinds of parameters for different uses, and all have their own definitions. Let's try a quick example below.

Let's say we want a list of random words. We can call the Random Words API in our terminal via cURL using `curl https://random-word-api.herokuapp.com/word?number=10` to get a list of ten random words. `/word` is a path parameter, which tells us where the information can be found. The `?` tells us where the query parameter begins. The number `10` is a variable, housed in the query parameter `number=`. You can change this number to list as many words as you want, even using `/all` to list all the random words the API contains. (If you're wondering, that list is 2115215 words long!) Another query parameter, `/?swear=0`, turns off swear words, in case you're using the Random Words API to teach young people computer science.

Conclusion

Parameters are a fundamental part of computer science, and understanding how users interact with your system will make you a better programmer and a better system designer.

API Parameters

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