SDK vs CLI vs MCP: choosing the right interface for your API (June 2026)

A developer considering which interface to implement for an API—SDK, CLI, or MCP server—must evaluate the needs of the user and the operational context, as these interfaces serve different purposes despite using the same backend. SDKs cater to application developers by providing typed methods for integration into production code, CLIs target operators and developers for scripting and automation tasks, and MCP servers are designed for AI agents that require tool invocation at runtime without human intervention. Each interface imposes different costs and maintenance overheads, with MCPs being notably more expensive in token consumption compared to CLIs. The choice between these interfaces often depends on the security model, the stability of the API surface, and the specific requirements of the consumer, such as authentication and compliance needs. Fern offers a solution by generating SDKs, CLIs, and MCP servers from a single API specification, ensuring synchronization across these interfaces as the API definition evolves.

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