MCP versus REST, function calling, and plugins
Words made simple
A few useful meanings before you read the explanation.
- Tool calling
- The model proposes using a named function and supplies its inputs. Application code checks permissions and runs the function.
- MCP
- A shared protocol for connecting AI applications to tools and resources. It does not replace permission checks or application security.
- AI
- Software techniques for tasks such as recognizing patterns, understanding language or generating content.
More words from this lesson
- API
- A way for one piece of software to ask another for data or an action. A claims API might return the current status of a claim.
- LLM
- A model trained to work with language. It can write or summarize text, but its answer still needs checking against reliable information.
- Agent
- An application that uses a model to choose its next action within defined limits. It can use tools and continue through several steps.
- Authentication
- Checking who a user or service is, such as by verifying a login session.
- Latency
- How long a request takes to return a result. Lower latency usually means a shorter wait for the user.
Overview
- REST is an HTTP API design style for application services.
- Function calling is a model interaction mechanism for proposing structured operations.
- MCP standardizes integration discovery and invocation/context exchange; a plugin is a packaging/integration mechanism whose exact meaning depends on its host.
Why this matters
Understanding these layers prevents rebuilding a backend or expecting a protocol to orchestrate the agent.
An everyday example
A menu, ordering language, kitchen process, and restaurant app are different layers of the same service.
A technical example
Model function call → MCP client → MCP tool server → existing REST claim API.
How it works
Use model tool calling for decisions, MCP for standardized integration, and domain APIs for authoritative operations.
Architecture and flow
LLM tool proposal → host policy → MCP invocation → REST/business API → result.
The insurance assistant example
The insurer keeps existing claim APIs and adds a narrow MCP facade for approved AI hosts.
When to use it
When multiple AI hosts need consistent discovery and tool/context access.
When to avoid it
Do not replace all internal REST APIs with MCP or describe MCP as a model or agent framework.
Interview answer
“Function calling is the model's decision interface, MCP is the integration protocol, and REST can remain the business-service interface behind it.”
Benefits, trade-offs, and production considerations
Added protocol layers introduce network latency, authentication flows, and operational ownership. Keep the MCP facade narrow and independently testable.
Can you explain it without the notes?
MCP versus REST, function calling, and plugins
Use your own words. Explain an example and one limitation before checking the explanation.
Check your explanation
REST is an HTTP API design style for application services. Function calling is a model interaction mechanism for proposing structured operations. MCP standardizes integration discovery and invocation/context exchange; a plugin is a packaging/integration…
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Practice this conceptAdapted from 13_AI.MD · “MCP versus REST, function calling, and plugins”. Examples are study fragments; framework behavior can depend on your version.