MCP explained: how it connects AI assistants with tools and data

Introduction

An AI assistant may need to look up information or perform an action outside the conversation. The Model Context Protocol (MCP) defines a common way to exchange messages between client applications and servers that offer capabilities such as tools and resources. MCP organizes the communication; it does not decide on its own whether an action is safe, appropriate or authorized for each user.

The components, without confusing their responsibilities

In a typical integration, the application hosting the model contains an MCP client that communicates with one or more MCP servers. The server may expose tools or give access to data and, in turn, interact with external services. The model may propose a tool call; the client application and the server implement the execution and access decisions of their environment.

MCP messages are encoded using JSON-RPC. The transports specification consulted defines stdio and Streamable HTTP as standard transports. stdio connects a client with a local process; Streamable HTTP uses HTTP requests and may use server-sent events. The choice changes the relevant controls: the local process needs execution and dependency controls; an HTTP service needs network and authentication controls suited to its context.

Authorization is optional for MCP implementations. When HTTP transport is used, the authorization specification states that implementations SHOULD conform to its mechanism. For stdio, they SHOULD NOT follow that flow and should instead obtain credentials from the environment. These words have a precise meaning: they are requirements and recommendations of the specification in context, not security guarantees.

A connection is not the same as trust

MCP does not make a server, a tool or the content they return trustworthy. Security depends on trust boundaries: who controls the server, what permissions it receives, what data it processes, which tools the model can invoke and how each action is validated. A secure design starts from limited permissions, minimal data and confirmations proportionate to the impact.

Conclusion

MCP standardizes a communication interface, not a universal security policy. To evaluate an integration, look at the client, the server, the model, the tools, the credentials and the external services as distinct parts.