MCP server cards and agent cards: what site owners should know
By Jahid Hasan
Well-known URLs for MCP and A2A are becoming part of the operational surface area of a modern site — similar to favicons, but for tooling.
If you are not shipping an MCP server yet, you can still benefit from understanding the shape of these files. They describe capabilities, transport, and safety-relevant metadata in a way clients can consume without scraping your marketing pages.
Cards are documentation that machines trust
A server card is not a replacement for human docs — it is the handshake. When it is wrong or stale, integrations silently rot because developers assume the card is authoritative.
Start small, publish honestly
Ship the minimum truthful card first, then iterate. Partial truth is worse than a narrow scope that is accurate and tested.