API Basics

Every agentic tool, from integrated development environment (IDE) agents to custom pipelines, ultimately sends HTTP requests to a model application programming interface (API) and processes the structured response, making direct API fluency the foundation for building anything beyond pre-built tools. You need to understand request anatomy, including authentication, endpoints, and model parameters, as well as response handling for token usage, finish reasons, and tool call outputs, and the differences between providers such as OpenAI's chat completions, Anthropic's Messages API, and Google's Gemini API. The API layer is also where you control cost, latency, and reliability through parameters like temperature and max_tokens, and where you implement production concerns like retries, fallback logic, and rate limit handling.