---
title: "What are MCP Servers?"
description: "This explainer clarifies what Model Context Protocol (MCP) servers do and where they differ from conventional APIs, serverless functions, and standalone appliances. It frames MCP servers as Alexa Skills that connect capabilities to an LLM, then as JSON-based APIs with multiplexing, server push, and built-in introspection for discovering tools, arguments, and usage descriptions. The post cautions that blindly generating an MCP server from an OpenAPI schema may expose low-level calls rather than agent-oriented workflows, and notes that MCP servers have a long-lived initialization, operation, and shutdown lifecycle rather than a serverless one. It also argues that MCP is not inherently secure or private, recommending remotely hosted servers protected by revocable bearer tokens, and envisions customized MCP-based agents becoming family-like assistants rather than mere appliances."
---

# What are MCP Servers?

[Fly.io](https://yomu.fyi/company/fly-io) · Jun 12, 2025

**Type:** Explainer

## Summary

This explainer clarifies what Model Context Protocol (MCP) servers do and where they differ from conventional APIs, serverless functions, and standalone appliances. It frames MCP servers as Alexa Skills that connect capabilities to an LLM, then as JSON-based APIs with multiplexing, server push, and built-in introspection for discovering tools, arguments, and usage descriptions. The post cautions that blindly generating an MCP server from an OpenAPI schema may expose low-level calls rather than agent-oriented workflows, and notes that MCP servers have a long-lived initialization, operation, and shutdown lifecycle rather than a serverless one. It also argues that MCP is not inherently secure or private, recommending remotely hosted servers protected by revocable bearer tokens, and envisions customized MCP-based agents becoming family-like assistants rather than mere appliances.

## Context

The standard description of MCP as a USB-C port for AI applications is presented as understandable but insufficiently concrete. The post supplies additional analogies and observations to explain what MCP servers connect, how they operate, and what their security and long-term role may be.

## Approach / What changed

It explains MCP through comparisons with Alexa Skills, HTTP 2.0-style APIs, and APIs with introspection, then contrasts MCP servers with serverless functions and appliances. It also discusses workflow-oriented tool design and recommends remote hosting with revocable bearer-token access as one component of a broader security approach.

## Takeaways

- MCP supports JSON requests and responses, multiplexing, server push, and standard requests that describe available tools, expected arguments, and intended usage.
- Generating an MCP server directly from an OpenAPI schema can expose low-level API building blocks; higher-level tools may better encapsulate workflows for agents.
- MCP servers have initialization, operation, and shutdown phases, and remote hosting can keep secrets away from an LLM client and other MCP servers when access is protected by a revocable bearer token.

**Tags:** [AI Agents](https://yomu.fyi/topic/ai-agents), [API](https://yomu.fyi/topic/api), [MCP](https://yomu.fyi/topic/mcp)

- Source: [Fly.io](https://fly.io/blog/mcps-everywhere)
- Source URL: https://fly.io/blog/mcps-everywhere
- Ingested by Yomu: 2026-09-03T01:24:03.214Z

[Read original post](https://fly.io/blog/mcps-everywhere)