What is an API key
An API key is a unique code assigned to a client so they can access an API. It works as an access credential, identifying the consumer and controlling what they can do. The client sends the key with each request so the service can authorize and track usage.
How an API key works
The API key is typically sent in a header or request parameter. The service looks up the key, checks whether it is active and what permissions it has. Based on the key, the service can restrict access to certain endpoints, define usage limits, and track metrics. Each key can have different access levels and expiration.
Practical example
A developer who wants to use an AI image generation API will create an account, receive an API key, and use that key in every request. The key ensures that only those with access can use the service and allows the provider to charge for usage or apply limits. Without the key, the request would be rejected because we are not authorized.
What API keys are for
API keys are used to authorize access, control usage of a service, track who calls what, and version. They allow providers to enforce limits, billing, and security. For the developer, they are a simple, standardized way to integrate external services securely. Each key must be unique, stored securely, and revoked when no longer needed.
Best practices
Store API keys in environment variables or secret managers. Never expose them in frontend code, public repositories, or logs. Use HTTPS for all communications. Revoke keys that appear to be exposed and generate new ones if necessary. Monitor usage per key to detect unauthorized access.