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What is an API Key and What is it Used for?

Angela Stringfellow

Last updated on

Many websites or applications we use have the facility to log in using Google or Apple credentials. This is made possible by Google and Apple allowing access to their log-in systems through the use of APIs. Before we dive into API keys, let’s briefly review what APIs are.

What is an Application Programming Interface (API)?

APIs are protocols that two computing systems use to communicate with each other – more specifically, APIs are the set of rules and syntax for ‌communication. The ‌systems cannot access the other’s internals, so the communication happens over the API layer which is separate from the internal systems.

Applications abide by the protocols defined for the required inputs and outputs and send requests to the API endpoints. Most APIs will have extensive documentation on how to communicate with the endpoints.

When an application developer wants to include a log-in with Google credentials, they’ll need to understand how to integrate Google sign-in with APIs into their app. The app must adhere to the rules and syntax prescribed by Google to access the information required to enable the Google sign-in. The developer and the application are unable to access the internal systems of Google and can only communicate with the API layer of ‌‌Google sign-in.

There are some APIs that can be accessed without authentication. But for others that require authentication when requests are sent to API endpoints, API keys are required to authenticate the request.

How API Keys Work

API keys are unique values that API providers use to identify and authenticate requests. This helps to ensure that the API provider gives access to the data or functionality only to approved users of the API service. API keys serve as the personal identifier for the user of the API. To gain API keys for a service, the developer must first register with the API provider. The API provider will then assign the developer a unique identifier or API key, which the application must pass along with the request to the API endpoints.

For API services that require authentication, every request should have an API key. The API service verifies the key for each request and if the API key is invalid, an error response is generated. If the API key is valid and the request is in the required format, the requested data is provided.

Application developers must ensure the API keys are kept secure. If a key falls into the wrong hands, it can be used to attack a service, and the attack will then be logged as if the developer were responsible.

Uses for API Keys

With the rise of microservices architectures and the need to communicate with various services, APIs have become widely used, with most services now requiring API keys for access. The major uses of API keys are discussed briefly in the following sections.


API services that require authorization cannot be used without API keys. Since every request should have an API key, they can be used to authenticate users. Requests to endpoints without API keys are rejected, and API requests without a valid key are also rejected. This way API keys help to ensure that only authorized users can access the service.


API keys are unique identifiers for each registered user of the API service, and the key must be used with every request. This helps the service ‌ identify who is sending that particular request.


The usage pattern of every user can also be tracked by API keys. The request, frequency, IP address, and various other parameters can all be tracked using the developer’s unique API key.


Most APIs have limits to their use, which can then be enforced with API keys. Since ‌user requests are tracked with the keys, it can be used to identify whether a user has exceeded the limits. Once the limit for an API key is crossed, additional data will not be provided to the user. Tracking users with keys can also be used to identify violators and block service to those users.


Requests to API services are logged and tracked with API keys. This is a record of how the service was used and by whom, and this log can be used to perform audits. For example, an audit can help to determine the root cause of a cyberattack or to analyze how users are using the service. This information can then be used to make improvements. Regardless of the purpose of the audit, API keys provide a simple way to perform audits of all the requests made to the service.

API Keys: Simple Yet Powerful

In summary, API keys are used to authenticate users to a service, but they also have a wide range of uses beyond authentication. All application developers and services today use APIs as a communication layer, which helps to make developers' lives easier.

For example, setting up a notification system is a cumbersome and time-consuming task, but you can register and gain access to an API key for a service like MagicBell to implement such a system. This ability to set up a complete notification system in mere minutes is made possible through the use of APIs and authentication with API keys.