Learning Center
May 22, 2023
6 min read

What are API Keys? Overview and Use Cases

Eric Pulsifer
Kong Content Team

Application programming interfaces (APIs) allow software to communicate and share data. But how can those APIs confirm the identity of the clients theyre communicating with? API keys are one solution.

API keys are unique codes for authenticating and authorizing access to the features, data, or resources offered up by an API. These keys allow builders and businesses to maintain control and monitor access over services and ensure security.

In this post, well further explain what API keys are, what they're used for, the types of API keys, and how to generate an API key.

What is an API key?

API keys are one of those great tech terms that are pretty well defined by the term itself. An API key can be thought of as an ID (or, dare we say, a key) for accessing an API. It can prevent unauthorized access to the potentially sensitive info applications might want to share with other applications.

The API key is usually a string of letters and numbers transmitted with the API call. Unlike a real ID, these keys can identify requests but not the users themselves.

What are API keys used for?

APIs may use API keys for security purposes as well as for monitoring or limiting usage.

The API key authenticates the client making a request. It also provides authorization letting the API know if the requesting application is allowed to use the API and what it can access.

Some common use cases for API keys include:

  • Security API keys can offer an extra layer of security for an API, better locking down data shared between API and client.

  • Access control With API keys, developers can make sure only authorized users have access to data or resources provided by an API.

  • Tracking and billing API keys can be useful in tracking and monitoring API usage. This information may be used for billing purposes or to keep tabs on (or enforce) rate limits.

  • Integration API keys can be used to integrate services or software so they can more freely communicate.

Overall, API keys play a part in software development by helping to ensure APIs are secure and used efficiently and responsibly.

Advantages of using API Keys

API keys offer a simple, effective solution for controlling, monitoring and securing access to applications and their data or resources. They also are enablers for creating new, innovative applications. The advantages of using API keys include security, access control, monitoring, usage tracking, and integration.

Let's take a bit of a deeper dive into a few of the big advantages.

Improved Security

API keys can offer an extra layer of security that gives developers and businesses control and visibility into the access of services, data, or resources.

  • Authentication API keys can authenticate access to an API. When used this way, they can make sure that only properly authorized parties or applications have access to APIs and they can revoke access as needed. With this approach, sensitive data is better protected from unauthorized access.

  • Authorization If you want to authorize access to certain resources or data, API keys can help by controlling access.

  • Monitoring Looking to detect (and prevent) malicious activity? API keys can help by allowing you to monitor API usage. When done properly, this can help organizations respond more quickly to potential security breaches.

Rate limiting With API keys, you can enforce rate limits to ensure APIs are used properly and efficiently and avoid denial-of-service (DoS) attacks.

Improved Performance

API keys can help with application performance by optimizing API usage, which can help with ensuring applications are responsive, scalable, and efficient.

  • Caching You can enable caching of the data from an API with API keys. Doing this allows developers to minimize the number of API requests and boost application performance by accessing cached data rather than making unnecessary new API requests.

  • Load balancing API keys can be used to balance API requests across servers or instances. This can reduce server load and enable greater scalability.

  • Monitoring Performance monitoring can help developers identify bottlenecks and drive optimization.

Rate limiting Beyond the security benefits of rate limiting touched on above, rate limiting with API keys also allows you to avoid overloading APIs, which can improve application performance.

Increased Flexibility

Developer flexibility can also be improved thanks to API keys in a few different ways.

  • Customization Developers can create API keys that offer unique access per each key. This customization helps control API access for users or applications.

  • Integration API keys can be used by developers to connect other APIs, allowing for integrated cross-application exchange of data and functionality.

  • Testing API keys can test API performance and functionality before theyre deployed to production.

  • Versioning By creating unique API keys for different versions of an API, developers can modify APIs without impacting existing applications.

What are the types of API keys?

There are many types of API keys. The type used will vary depending on the use case and security requirements. Selecting the right type of API key helps protect sensitive data and minimizes unauthorized access.

  • Public API keys These are most often used for read-only access to public data. These may be embedded in client-side applications.

  • Secret API keys These are used for access to sensitive data (and may include write access). As the name implies, these are secret and shouldn't be shared publicly. These are often found in server-side applications.

  • JWT-based API keys These use JSON Web Tokens (JTWs) for API-access authentication and authorization (most typically in modern web applications).

  • Session-based API keys These are temporary keys used to grant access for a short session before expiring.

  • Scoped API keys These are used to limit the features or resources offered by an API to control access.

Client-side API keys vs server-side API keys

Client-side API keys and server-side API keys are used in different places and secured in different ways.

Client-side keys are used in client-side applications (as the name implies) to access public data or handle read-only operations. These API keys are exposed to users and applications and aren't intended to be kept secret. They're regularly used for rate limiting or caching.

Server-side API keys are used in you guessed it server-side applications or command-line tools. These keys can be used to perform write operations or access sensitive data. These keys are considered more secure as they are kept secret, not exposed to end-users, and are often used for authentication and authorization.

Choosing between server-side and client-side API keys depends on your use case and your APIs security requirements. For public data or read-only operations, client-side API keys can be great, but for sensitive data or write operations, server-side API keys are the way to go.

How to generate an API key

When it comes to generating an API, the process depends on the API platform or service you're using. Typically this will involve logging into the service and the appropriate section or setting, selecting the type of key you want to generate, naming or offering a descriptor for the key, and then copying and storing the key in a password manager or encrypted file.

As with physical keys, it's important to keep API keys secure. That means you probably don't want to be sharing them publicly and ideally will store them in a safe location and rotate them from time to time to help minimize the risk of any unauthorized access.


In this post, we talked about what API keys are, how they are used, and the types of API keys you may come across.

These unique codes for authenticating and authorizing access to an APIs features, data, or resources. Using API keys (and using the right keys for the right use cases) is just one part of larger efforts to monitor access, maintain control, and ensure security.