MCP overview

GetRatesAPI runs a hosted Model Context Protocol (MCP) server that exposes rate data and a few extra capabilities (conversion, asset listings, usage) to MCP-capable clients.

Transport

Streamable HTTP, single path /mcp.
SDK: github.com/modelcontextprotocol/go-sdk v1.8.0.
Binary: cmd/mcp.

Auth

Identical API-key scheme to REST: Authorization: ApiKey <key>. There is no separate MCP-only credential, and no OAuth — this is an explicit, documented deviation scoped to pre-production.

Tools

Tool	Billable	Description
`get_rate`	yes	Read a stored direct currency rate
`convert_currency`	yes	Convert an exact decimal amount using a stored direct rate
`list_fiat_currencies`	no	List fiat assets in stored current rates
`list_crypto_assets`	no	List crypto assets in stored current rates
`get_usage`	no	Read your account’s current request-unit usage

convert_currency, list_fiat_currencies, and list_crypto_assets are the only place these three capabilities exist in the product today — there is no equivalent REST endpoint for any of them. See REST API overview for why.

Error model

Tool-call domain errors differ from REST’s HTTP-status model: they are returned as CallToolResult{IsError: true} with the same {code, message, request_id} fields (plus limit/remaining/reset_at for quota_exceeded) inside the structured content — not an HTTP status code. Auth failures (missing/invalid API key) remain ordinary HTTP 401, before any MCP tool call is attempted.

Getting started

See Hosted MCP setup to run the MCP server locally, then pick a tool page above for its exact input/output schema and examples.