# MCP Explained: The Model Context Protocol for Agent Tools Source: https://hlab.in/blog/mcp-model-context-protocol-explained [Blog](https://hlab.in/blog) MCP Explained: The Model Context Protocol for Agent Tools # MCP Explained: The Model Context Protocol for Agent Tools reading time 2 min published 5 Nov 2026 industry AI agents MCP is the open standard for connecting AI agents to tools and data. Learn servers, clients, tools, resources and the security habits that matter. Industry [AI agents](https://hlab.in/industries/ai-agentic-development) Topics [AI Agents](https://hlab.in/blog/tag/ai-agents)[Software Architecture](https://hlab.in/blog/tag/software-architecture) Published 5 Nov 2026 Reading time 2 min [Let’s talk growth](https://h.hlab.in/contact) On this page - [The pieces](#the-pieces) - [Where MCP sits](#where-mcp-sits) - [Designing a good MCP server](#designing-a-good-mcp-server) - [Security habits that matter](#security-habits-that-matter) - [When to build one](#when-to-build-one) - [The takeaway](#the-takeaway) Before a standard existed, every AI app wrote its own connector for every tool: one for the calendar, one for the database, one for the ticket system. Each pair needed custom code. The **Model Context Protocol (MCP)** replaces that with one interface. **MCP is an open protocol, introduced by Anthropic in 2024, that lets AI applications connect to external tools and data sources in a standard way.** It is now widely supported across agent products and editors, and it is governed as an open standard. ## The pieces ``` flowchart LR H["Host app (assistant, IDE)"] --> C["MCP client"] C <-->|"JSON-RPC"| S1["MCP server: files"] C <-->|"JSON-RPC"| S2["MCP server: database"] C <-->|"JSON-RPC"| S3["MCP server: ticketing"] ``` - **Host and client.** The AI application embeds an MCP client for each server it connects to. - **Server.** A small program that exposes capabilities from one system. - **Tools.** Actions the model can call, such as “create issue” or “run query”. - **Resources.** Read-only data the app can load into context, such as a file or record. - **Prompts.** Reusable prompt templates a server can offer. - **Transport.** Messages use JSON-RPC. Local servers commonly run over standard input and output, and remote servers over HTTP with streaming. Write a server once and any MCP-aware app can use it. Write a client once and it can use any server. ## Where MCP sits MCP covers the agent-to-tool boundary. It does not define how agents talk to each other (see [A2A](https://hlab.in/blog/a2a-agent2agent-protocol)) or how an agent talks to a user interface (see [AG-UI](https://hlab.in/blog/what-is-ag-ui)). ## Designing a good MCP server - **Expose few, well-named tools.** Clear names and descriptions are what the model reads to choose. - **Return useful errors.** “Project ID not found, valid IDs are…” lets the agent recover. - **Keep outputs small.** Return summaries and pagination, not whole tables. - **Make actions safe to repeat** where possible, or require confirmation for destructive ones. ## Security habits that matter - **Least privilege.** Give each server the narrowest credentials it needs. - **Treat tool output as untrusted input.** A web page or document returned by a tool can contain instructions meant to hijack the agent. This is prompt injection. - **Review third-party servers** like any dependency: read the code, pin versions. - **Require approval for write actions** such as sending email, deleting data or spending money. - **Log every call** with arguments and results. ## When to build one Build an MCP server when several agents or apps need the same capability, or when you want your product to be usable by agents. For one app calling one internal function, a direct function call is simpler. ## The takeaway MCP turned tool integration from an N-by-M problem into a shared standard. Use it for tool access, design servers with small, clear tools, and apply the same security care you would to any API that can take actions. ## Explore more articles - AI agents ### ANP: The Agent Network Protocol and the Open Web of Agents 2 min read 4 Nov 2026 [ANP: The Agent Network Protocol and the Open Web of Agents](https://hlab.in/blog/anp-agent-network-protocol) - AI agents ### What Is A2A? The Agent2Agent Protocol Explained 2 min read 2 Nov 2026 [What Is A2A? The Agent2Agent Protocol Explained](https://hlab.in/blog/a2a-agent2agent-protocol) - AI agents ### AP2 Explained: How AI Agents Can Pay Without Losing Trust 2 min read 3 Nov 2026 [AP2 Explained: How AI Agents Can Pay Without Losing Trust](https://hlab.in/blog/ap2-agent-payments-protocol) ## Next stop: a 30-minute call. Tell us what you are building. A senior lead will tell you honestly what it takes to ship it and take it to market. [Let’s talk growth](https://h.hlab.in/contact) [Email us](mailto:business@hlab.in)