Adapting an API for the Model Context Protocol (MCP) can start with a server that calls existing endpoints. The substantial work is making those capabilities understandable and reliable for an AI assistant, which discovers tools and selects operations from their descriptions and schemas.
The first challenge is tool design. Exposing every endpoint can produce an unwieldy catalogue. A practical approach is to define focused business operations with clear descriptions, constrained inputs, and structured results. For example, find_customer followed by get_customer gives the assistant a clear path from a human name to a specific record.
Security and authorization require careful attention, particularly when an MCP server mediates access to another API. Preserve user permissions and tenant boundaries throughout that chain. For OAuth deployments, validate tokens intended for the MCP server and manage downstream credentials appropriately: accepting tokens intended for another service and blindly forwarding them is prohibited by MCP’s authorization rules.
Reliability and context management also need deliberate design. Plan for timeouts, rate limits, pagination, and retries. Protect writes against duplicate execution, keep responses focused, and return actionable errors. MCP distinguishes protocol errors from tool execution failures that an assistant can use to adjust its request. Test complete workflows, including ambiguous searches and partial failures.
Entity identification introduces another question: are URNs necessary? URNs are optional. MCP resources require a URI, and a Uniform Resource Name is one form of URI intended for persistent, location-independent identification. MCP permits other URI schemes, including custom ones.
For a resource accessed through MCP, a custom URI might look like crm://tenants/acme/customers/123. An HTTPS URL is another option when the client can retrieve the resource directly. Separately, tools can accept ordinary business identifiers: an existing API ID, a UUID, or a combination such as tenant_id and customer_id. Those tool parameters do not need URI formatting, and exposing tools does not require exposing every entity as an MCP resource.
The deeper challenge is entity resolution: determining which “Acme” the user means and whether records in different systems represent the same organization. A practical design returns stable, scoped identifiers from search tools and reuses them in subsequent calls. URNs can support consistent naming across systems, but adopting them still requires lookup logic, identity mapping, and authorization checks. Choose them when their persistence and namespace conventions solve a concrete integration need.
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