> For the complete documentation index, see [llms.txt](https://docs.fastnode.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.fastnode.io/getting-started/authentication.md). # Authentication Every FastNode request is authenticated by your API key, passed directly in the URL path: ``` https://.fastnode.cc// ``` For example, BNB Smart Chain: ``` https://bsc.fastnode.cc/YOUR-API-KEY/ ``` ## Key format FastNode API keys start with the `FN` prefix and are **64 characters** long — e.g. `FNxxxxxxxxxxxx…`. Keys are issued automatically and sent to your email when you order a node or request a test. ## Notes * Endpoints are issued with a trailing slash (`…/YOUR-API-KEY/`) — use them exactly as provided. * Because the key travels in the URL, it can end up in server logs and browser history. Keep keys server-side, never embed them in client-side code, and rotate a key immediately if it leaks. ## Errors A missing or invalid key returns `401 Unauthorized`. See [Error Codes](/reference/error-codes.md) for the full list. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.fastnode.io/getting-started/authentication.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.