MCP vs. Semantic Kernel: Protocol, Agent Orchestration, and Enterprise Project Selection

The Bottom Line: MCP Handles Connectivity, Semantic Kernel Handles Orchestration

MCP and Semantic Kernel operate at different abstraction layers.

MCP (Model Context Protocol) is a standard protocol for client-server communication. It defines how to initialize connections, discover tools, read resources, retrieve prompt templates, and invoke tools, but it does not dictate how an application should select models, maintain agent state, or organize end-to-end business workflows.

Semantic Kernel is an application development SDK provided by Microsoft. It organizes capabilities from native code, OpenAPI specifications, or MCP servers into Plugins, then leverages model Function Calling to handle function selection, parameter passing, and result return. When you need agents, plugin dependency injection, or in-app service orchestration, Semantic Kernel serves as the primary layer of operation.

Therefore, in real-world projects, the relationship between them is more accurately described as follows:

用户请求
  ↓
Semantic Kernel：模型、Plugin、Agent、审批与业务编排
  ↓
MCP Client：发现并调用外部能力
  ↓
MCP Server：文件、数据库、SaaS、内部 API

Core Differences Comparison

Dimension	MCP	Semantic Kernel
Essence	Open client–server communication protocol	In-app SDK and AI orchestration framework
Primary Responsibility	Standardizes exposure of Tools, Resources, and Prompts	Organizes Plugins, Function Calling, Agents, and application services
Execution Boundary	Cross-process, cross-client, or remote services	Typically runs within your application process and service architecture
Capability Discovery	Client dynamically discovers via tools/list protocol methods	Kernel registers and imports Plugins at app startup or runtime
Tool Execution	Client invokes Server via tools/call	Model requests a function; Kernel routes to the corresponding Plugin Function
Transport Mechanism	Local stdio or remote Streamable HTTP	In-process calls, HTTP APIs, OpenAPI, or MCP Plugin
Best For	Multi-client tool sharing, cross-language integration, remote capability service	Enterprise app orchestration, dependency injection, Agent workflows, and business permission control
Composability	Can be integrated as an external capability layer	Can import MCP Servers as Plugin sources

Relationship Between MCP, Semantic Kernel, and Function Calling

These three concepts are often conflated, but they actually correspond to three distinct layers.

Function Calling: The Invocation Format Between Models and Functions

Function Calling addresses how models generate function names and arguments based on function descriptions, after which the application executes the function and returns the result to the model. It is the lightest layer, suitable for a small number of stable functions used exclusively within the current application.

Semantic Kernel: Organizing Functions into Maintainable Application Capabilities

Semantic Kernel Plugins are groups of functions with semantic descriptions. Plugins can originate from:

• Existing native code in C#, Python, or Java;
• OpenAPI specifications;
• MCP Servers.

The Kernel handles function registration, dependency injection, model invocation, and routing Function Calling requests to the correct Plugin. Business logic such as authentication, approval workflows, retries, and state management should still be controlled by the application code.

MCP: Decoupling Capabilities from Individual Applications

When the same files, databases, or SaaS capabilities need to be provided to multiple AI clients simultaneously, writing custom Plugins for each application leads to redundant integration efforts. An MCP Server exposes these capabilities through a unified protocol, allowing different hosts to discover and invoke them using their own MCP Clients.

When to Use Only Semantic Kernel

Do not introduce MCP in the following scenarios:

1. You have only one backend application and a small number of internal functions;
2. Functions depend on database connections, caches, or domain services within the current process;
3. There is no need to share capabilities across Cursor, Claude Desktop, VS Code, or other clients;
4. The tool list is fixed and does not require runtime discovery;
5. Your team focuses more on Agent orchestration, approvals, and business state rather than cross-client protocol compatibility.

In these cases, directly injecting business services into Semantic Kernel Plugins results in a simpler structure that is easier to debug.

When to Prioritize MCP

The following scenarios are better suited for implementing capabilities as an MCP Server:

1. The same tool needs to be reused by multiple AI Hosts;
2. Tools are maintained by different languages or teams;
3. There is a need to discover tools, resources, or prompt templates at runtime;
4. Local tools must connect to desktop clients via stdio;
5. Remote capabilities must be provided to multiple users via Streamable HTTP;
6. You want to decouple the tool service from Agent orchestration for independent publishing and upgrades.

Note: MCP standardizes only the connection method; it does not automatically handle tenant isolation, least-privilege access, auditing, rate limiting, or approval workflows for high-risk operations.

Recommended Combined Architecture

Enterprise projects can combine both into a four-layer architecture:

1. Application Layer
   API、Web、桌面端、用户身份与业务权限

2. Semantic Kernel Layer
   模型路由、Plugin 注册、Agent 编排、Human-in-the-loop

3. MCP Client Layer
   Server 连接、能力协商、工具发现与调用路由

4. MCP Server Layer
   文件系统、数据库、CRM、监控平台、内部 API

In this architecture:

• Semantic Kernel does not have unrestricted access to databases or files;
• The MCP Server only exposes a curated set of tools and resources;
• High-risk write operations require human confirmation at the application or plugin layer;
• Every Tool Call is logged with the user, server, tool name, parameter summary, and execution result;
• Local tools use stdio, while remote shared services use Streamable HTTP with authentication.

A Practical Selection Decision Table

Scenario	Recommended Approach
A single .NET service calling 5 internal functions	Semantic Kernel Plugin
An agent needs to orchestrate multiple business plugins	Semantic Kernel
Both Cursor and an internal chatbot need to access the same documentation tools	MCP Server
A multi-language team needs to share the same tool interfaces	MCP Server + individual MCP Clients
A Semantic Kernel Agent needs to call remote CRM tools	Semantic Kernel + MCP Plugin
You only need the model to output a function name and parameters	Native Function Calling

Common Misconceptions

Misconception 1: Using MCP eliminates the need for an Agent framework

MCP does not handle the complete agent decision loop, business state management, or human approval workflows. It provides connectivity and capability exchange; orchestration must still be handled by the host, Semantic Kernel, LangGraph, or your custom business code.

Misconception 2: Semantic Kernel Plugins can only be written in local code

Plugins are not limited to native code; they can also be imported from OpenAPI specifications or MCP Servers. When cross-platform sharing is required, you can gradually extract mature capabilities from in-process plugins into standalone MCP Servers.

Misconception 3: All functions should be refactored into MCP Servers

Splitting simple functions used by only a single service into independent servers increases process overhead, connection management, authentication complexity, and operational costs. The decision to use MCP should be driven by “the need for cross-boundary reuse and governance,” not by technical hype.

Final Recommendations

• Single application with few internal functions: Start with native Function Calling or Semantic Kernel Plugins.
• Need for agent orchestration and enterprise application integration: Use Semantic Kernel as the primary framework.
• Need for cross-client, cross-language, and remote shared tools: Package stable capabilities as MCP Servers.
• Complex enterprise systems: Let Semantic Kernel handle orchestration and MCP handle connectivity. They work best as a combination, not as mutually exclusive choices.

Continue Reading

• MCP vs. Function Calling: Real-world selection, API Gateways, and composite architectures
• MCP JSON-RPC Parse Error Troubleshooting: stdout, stdio, and Tool list failures
• Practical Guide to Deploying MCP over Streamable HTTP
• MCP Deep Dive: Protocols, Deployment, Security, and Troubleshooting
• AI Agent Architecture: From Tool Calls to Production-Grade Orchestration

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