API Key
A simple token passed with API requests to identify the calling project or application. Not a substitute for user authentication but useful for rate limiting and usage tracking.
What is API Key?
A simple token passed with API requests to identify the calling project or application. Not a substitute for user authentication but useful for rate limiting and usage tracking.
API Key is a intermediate-level concept that sits in the Security Architecture area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.
If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "API Key" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.
Learn API Key in depth
Full interactive lesson with diagrams, code examples, real-world references, and a quiz.
Open the API Key lessonRelated lessons
Lessons that touch on API Key as part of a larger topic.
API Keys
The simplest way to identify and authenticate API consumers, a shared secret with limits
intermediate · api design protocols
API Keys
Simple tokens for identifying and authenticating API clients, not users
intermediate · security architecture
Service-to-Service Authentication
How microservices prove their identity to each other, mTLS, JWTs, API keys, and SPIFFE
intermediate · security architecture
Secrets Management
Storing, accessing, and rotating sensitive credentials. API keys, database passwords, tokens, and certificates
intermediate · security architecture
See also
Related glossary terms you might want to look up next.
JWT
JSON Web Token: a compact, self-contained token for transmitting claims between parties. The server can verify it without a database lookup.
OAuth
An authorization framework that lets users grant third-party apps limited access to their accounts without sharing passwords. Powers 'Sign in with Google.'
Rate Limiting
Controlling how many requests a client can make in a given time window. Protects your API from abuse and ensures fair usage.