I wanted to use the Bullion API from an agent, so I could ask a question about gold and get an answer back with the figure, the date and the source attached.
The obvious way to do that is to give an agent an API key. Then it can do anything the key can do. That didn't feel right for a service holding someone's portfolio and their transaction history, so I built the MCP server read-only instead.
It has no write tools at all, so there is no write permission to grant in the first place. An agent can look things up and it can never change anything.
What an agent can ask
The tools cover the same ground as the REST API. Metal prices and price history, the derived gold metrics, central-bank holdings and reserves, inflation, policy rates, bond yields, government debt, and your own portfolio if you approve the scope for it.
The server is at https://api.bullionapi.dev/mcp and it uses OAuth 2.1, so you sign in and approve exactly what it may read. Any agent that supports remote MCP servers with sign-in can connect, including Claude, ChatGPT, Cursor, VS Code and Gemini CLI. The agent registers itself the first time it connects. The setup steps are on the MCP documentation page.
What I use it for
Mostly questions that mix a price with the context around it. A gold price on its own is half an answer. What changed, what the policy rate is, whether a central bank is still adding, what inflation has done to the price since I bought. The agent pulls the pieces together in one answer instead of handing me a list of endpoints I have to stitch together myself.
I also wrote a public plugin with two skills for it, one for market analysis and one for portfolio review, so an agent that installs it knows how to use the tools instead of guessing.