The guide offers a detailed approach to creating effective API documentation that is designed to be intuitive for both human developers and large language models (LLMs), using examples from notable companies like Stripe, Twilio, and Pinecone. It highlights the importance of clear, structured documentation that facilitates a smooth developer experience, emphasizing the role of documentation in driving API adoption and reducing the support burden. Common pitfalls such as context mismatch, outdated content, and documentation locked behind authentication walls are discussed, alongside strategies for overcoming them. The guide underscores the need for comprehensive API references, practical guides, visible changelogs, and effective error handling to enhance usability and trust. By treating documentation as a product, with assigned ownership and regular audits, developers can ensure their APIs are easily understandable and usable, ultimately leading to faster adoption and fewer support issues.