Imagine that we have artificial intelligence (AI) and large language models (LLM) as intelligent as the human brain. However, if these "super brains" are confined to their own worlds, unable to access real - time external information or use external tools, their capabilities will be significantly diminished. How to enable them to interact safely and efficiently with external data (such as libraries) and services (such as online tools) has become a core issue that needs to be addressed urgently.

• *MCP (Model Context Protocol) emerges as the times require. It is like a professional "diplomat", formulating a set of standardized "communication etiquettes" that allow AI models to smoothly communicate and collaborate with various external resources.

MCP provides several different "communication methods" (transmission mechanisms), among which three are the most notable: Stdio, SSE, and Streamable HTTP. They are like different means of transportation, each with its own advantages and disadvantages, suitable for different "road conditions" (application scenarios). Understanding their differences is the key to selecting the best "travel plan" for our AI applications.

1. Stdio stdio: The "direct connection expressway" within the local computer

Stdio is like two programs communicating face - to - face by "passing notes" inside the same computer.

1. Communication principle

• Method: It is carried out through the standard input (stdin) and standard output (stdout) inside the computer. The client program starts the server program (as a sub - part of it), and then they are like making a phone call, sending and receiving information (messages in JSON - RPC format) through the internal pipeline with each message ending like "hanging up" (separated by a newline character).

• Example: Your AI assistant needs to read a local file on your computer or analyze local chat records (such as WeChat), but you don't want these private data to be sent over the network.

2. Core advantages

• Zero network dependency 🚫🌐: It doesn't require an internet connection, nor does it need to set up a complex network. It is very suitable for development and testing on your own computer.
• High security 🔒: Data only flows inside your computer and won't go outside, ensuring privacy.
• Low latency ⚡: It is directly transmitted through memory or internal pipelines, with high speed and efficiency.

3. Limitations

• One - to - one service 🧍‍♂️: A server program usually can only serve one client at a time and can't handle many requests simultaneously. It is not suitable for large - scale applications.
• Local limitation 🏠: It can only be used on the same computer and cannot access resources on other computers or in the cloud.

Applicable scenarios: Integration of local small tools, handling personal privacy data, and quickly testing the effect of a functional prototype.

2. SSE sse: The network - based "one - way broadcast station" 📡➡️📱

SSE is like establishing a "broadcast channel" from the server to the client. The server can continuously send information to the client, but the client has to use another way to "reply".

1. Communication principle

• Method: It utilizes standard web technologies (HTTP long - term connection). The server needs to open two "windows": /sse window (GET request): The client connects to the server through this window, establishing a long - term online channel specifically for receiving the "broadcasts" (event streams) pushed by the server. /messages window (POST request): If the client wants to send requests or data to the server, it needs to knock on this "window's" door.
• Conceptual illustration:

• Example: You have opened several web pages, all of which need to see the real - time progress update of a task on the server or monitor changes in a remote database.

2. Core advantages

• Supports remote access 🌍: It can connect to servers that are not on the same computer, suitable for distributed systems.
• Real - time performance ✨: The server can actively and in real - time push the latest messages to the client, such as task progress bar updates.

3. Limitations

• High server pressure 💪: It needs to maintain the connection all the time. If there are many clients, the server load will be relatively heavy.
• Mainly one - way push ➡️: Although the client can also send requests, it is mainly designed as a one - way information flow from the server to the client. Implementing complex two - way real - time interaction is relatively troublesome.
• About to be "retired" ⏳: The official believes there is a better way and plans to replace it with Streamable HTTP below.

Applicable scenarios: Remote services that require the server to push real - time notifications to the client (such as status updates of online collaboration tools), or scenarios with high requirements for compatibility with old browsers.

3. Streamable HTTP streamable_http: The flexible and compatible "next - generation expressway" 🛣️🚀

Streamable HTTP is an upgraded version of SSE. It is more like a modern expressway that allows two - way traffic, and it is more flexible and compatible.

1. Communication principle

• Method: It is completely based on the standard HTTP protocol. There is no longer a need for a dedicated /sse window, and all communication goes through the unified "gate" of /message.
• Dynamic upgrade 🔄: The server can, as needed, "upgrade" an ordinary HTTP request into a continuous streaming connection (like SSE) for real - time pushing of continuous data. It can also "downgrade" back to an ordinary request at any time.
• Conceptual illustration:

2. Core advantages

• Friendly to statelessness ☁️: The server doesn't need to remember who is connecting. Each request is processed independently, which makes it easier for the server to manage and scale (especially in the cloud).
• Compatible with infrastructure 👍: It can work well with modern network facilities such as CDN (Content Delivery Network), API gateways, and load balancers.
• Flexible stream processing 💧: When a large amount of continuous data needs to be pushed in real - time (such as the sentence - by - sentence display when an AI generates a long article), it can easily switch to streaming transmission; for ordinary requests, it uses the ordinary method.

3. Limitations

• A bit more complicated 🤔: If session management is required (such as tracking multiple requests from the same user), developers may need to do more work on their own.

Applicable scenarios: Cloud functions (such as AWS Lambda), distributed systems that need to scale automatically according to the load, and stateless service architectures. This is the currently recommended remote communication method by the official.

4. Comparison summary: Which one should I use?

Selection suggestions:

• Only for use on your own computer? 👉 Choose Stdio, simple and straightforward.
• Need to connect to a remote server? 👉 Directly use Streamable HTTP to embrace the future and avoid code modification later.

5. Future outlook: The evolution path of MCP

The MCP protocol is still evolving, aiming to make the connection between AI models and the external world smoother and safer. According to the plan (such as the roadmap for 2025), the following aspects will be emphasized in the future:

• Remote secure connection 🔒: For example, using the standard OAuth 2.0 authentication method to ensure that the connection is authorized.
• Service discovery 🗺️: Enabling AI models to more easily find and connect to available external services.

These improvements will further promote the seamless integration of AI agents with a wide range of Internet resources and services, making AI more powerful and practical.