Application Programming Interface (API)

An API (application programming interface) describes how to call a service programmatically: which URLs, parameters, and response formats apply. Almost all LLM providers expose HTTP APIs to send prompts and receive output.

In automation, tools like n8n connect API calls with webhooks. For agents, APIs often become tools the model can use through MCP or similar tool-routing logic.

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Key characteristics

• Formalizes system communication with clear endpoint contracts, parameters, and response formats.
• Is a core building block when connecting LLM services to apps, databases, and automations.
• Requires authentication, error handling, and versioning to stay stable in production.