Market data inside your AI app: the MCP servers worth knowing

The Model Context Protocol turned market data into something you can ask questions of directly, in the app you already work in. Several providers now ship one, so the question has moved from whether you can do this to whose tools you want your model calling. Here is the field, and the things that actually separate a useful connector from a thin wrapper.

What separates a good MCP server from a thin one

Tool descriptions are runtime, not documentation. They are the only thing the model reads when deciding which tool to call and how to interpret the result. Vague ones produce tools that are either never called or called for things they cannot do.

Annotations have to be per tool and correct. Read-only, destructive, idempotent, open-world — clients use these to decide what to run without asking you first. A write tool mislabelled as read-only gets executed silently. We shipped that inversion once, on our own alert tools, and it is why we check it mechanically now.

Refusals should be machine-readable. When a tool cannot answer, a named reason code lets the model say something true. An empty result lets it say the market is quiet.

New tools should appear without reconnecting. A server that changes its tool list should say so; a client that has to be restarted to see a tool you are paying for is a bad experience nobody warns you about.

Free before paid

The most useful thing about an MCP data server is that you can evaluate it before paying. Ours exposes 20 of 33 tools with no key at all — delayed or aggregate by design, and complete within that. Point a client at the URL and ask it something. What you learn in ten minutes about error handling, freshness fields and description quality is what the paid tier is like too, because it is the same code with more rows.

What ours is for

Asking a question that spans both books and getting an answer with its sources named. Is BTC stretched the same way the index is? What did the map look like when this last happened? Alert me when the flip moves more than this. All three are one sentence in a chat window and none of them are a single REST call. See the MCP and API or the journal on connecting it.