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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsNo—MCP does not replace function calling. MCP standardizes how an application connects to tools exposed by servers; the host application still sends tool definitions to its chosen model API, handles the model’s returned tool call, and routes it through an MCP client.
What MCP handles—and what it doesn’t
The Model Context Protocol (MCP) is an open standard for connecting AI applications to the systems where data and tools live. An MCP server exposes tools; an MCP client lets a host application discover and invoke them. The protocol supplies the connection and tool operations, not the complete model-facing decision loop. The MCP TypeScript SDK v2 overview describes that SDK line as implementing the 2026-07-28 specification; check the SDK and protocol version used by your application because interfaces can change.
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In the documented TypeScript flow, the host asks the MCP client for the server’s tools, sends their definitions to a tool-calling model API, then routes any returned tool call back to the client. The model API request and the conversation orchestration remain the host’s responsibility.
Which layer does each job?
| Responsibility | MCP client and protocol | Host and model API |
|---|---|---|
| Discover tools | The client lists tools and retrieves their definitions. MCP TypeScript SDK overview | The host receives the definitions for use in a model request. TypeScript SDK client guide |
| Decide whether a tool should be called | The cited SDK flow does not establish a universal model decision mechanism. | The host sends definitions to a tool-calling model API, which may return a tool call. TypeScript SDK client guide |
| Invoke the selected tool | The client offers an operation such as callTool to invoke a named tool with arguments. MCP TypeScript SDK overview |
The host routes the model-returned name and arguments to the client. TypeScript SDK client guide |
| Continue the conversation | The client returns the tool result. MCP TypeScript SDK overview | The host adds that result to the conversation and continues the model interaction as needed. TypeScript SDK client guide |
The model-to-MCP tool-call flow
The TypeScript SDK’s “Build your first client” guide describes the handoff plainly: “when the model returns a tool call, pass its name and arguments to callTool unchanged and append result.content as the tool result.” That means the model’s function call is not itself an MCP invocation; the host translates the model’s choice into a client operation.
#1 Best Overall
- Connect an MCP client to an MCP server.
- Call
listTools()to obtain the available tool names, descriptions, and input schemas. - Include the definitions in a tool-calling request to the model API selected by the host application.
- If the model returns a tool call, pass its name and arguments to the MCP client’s
callTool()method. - Add the returned tool content to the conversation and continue the model interaction according to the application’s flow.
The exact request shape, model response format, and conversation handling depend on the host, model API, SDK, and protocol version. The guide documents a TypeScript SDK example; it does not imply that every provider or host uses an identical interface.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Does this apply beyond the TypeScript example?
The C# SDK’s API reference describes McpClientTool as enabling integration with AI models that support function-calling capabilities. That corroborates the separation: MCP client tools can be presented as model functions, while an application still integrates them with the model. It is not evidence that all model APIs expose the same function-calling format. See the MCP C# SDK API reference.
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