Chapter L6.2 — MCP custom

Level 6 — Advanced. Product details verified on 24/06/2026 against official sources.

Goal

By the end you’ll understand what MCP is in plain terms, when you need a custom MCP server instead of a ready connector, how to add one to Claude Code, and the pattern that combines a skill with an MCP. It’s the way to connect Claude to what doesn’t already have an integration.

Prerequisites

Having used connectors (ch. L3.3).
Claude Code installed (ch. L2.2), for the hands-on part.

What MCP is, in plain terms

MCP (Model Context Protocol) is an open standard for connecting Claude to external tools and data. Think of a universal power socket: instead of a custom-built integration for each app, MCP defines a common way for Claude to talk to a service. An MCP server is the component that exposes that service’s actions to Claude.

The connectors in ch. L3.3 are already MCP under the hood: a custom connector is a remote MCP (a server reachable over the network). MCP is therefore the technical layer that sits beneath connectors.

When you need a custom MCP

The connector directory covers the most common apps. A custom MCP is needed when:

the app you need has no ready connector;
you want to connect one of your internal tools or a company database;
you need a specific action that no existing connector offers.

In short: first you search the directory; if it’s not there, you build or connect an MCP.

Local or remote

An MCP server can run in two ways, and Claude Code handles both.

Table L6.2.1 — Local and remote MCP compared.

Type	Where it runs	How
Local (stdio)	on your computer	child process
Remote (HTTP)	on a server	over the network

The local one (stdio transport) is started by Claude Code as a child process that communicates over standard input/output: handy for tools that live on your machine. The remote one (http transport) is a server reachable over the network: it’s the form of custom connectors, reached from Anthropic’s cloud (ch. L3.3).

Adding an MCP to Claude Code

From the terminal, the base command is claude mcp add. For a local server:

claude mcp add --transport stdio \
  my-tool -- npx -y my-mcp-server

The flags (--transport, --env, --scope) go before the name; the -- separates the name from the command that starts the server. Environment variables are passed with --env (for example a service’s API key).

Warning: a custom MCP gives Claude access to an external service. Only connect servers you trust, and don’t put secrets in the clear: use environment variables.

The skill + MCP pattern

MCP and Skills solve different problems and complement each other. An MCP gives Claude the capability to access a service (the data, the actions). A skill (Level 5) gives Claude the method: when to use that capability, in what order, with what rules.

Example: an MCP exposes your management software; a skill describes the workflow “how to prepare the monthly report from the management software’s data.” The MCP is the arm, the skill is the procedure. Together they make an integration not just possible, but repeatable.

In practice: connect a tool

First check the connector directory (ch. L3.3): if it’s there, use that.
If it’s not, obtain or write an MCP server for your tool.
Add it with claude mcp add, choosing stdio (local) or http (remote).
Pass credentials with --env, never in the clear.
If you use it recurrently, write a skill that describes its workflow.

Common mistakes

Building an MCP that already exists. Check the connector directory first.
Flags after the name. They go before; the -- separates them from the server’s command.
Secrets in the clear. Use --env/environment variables, don’t write them in the command.
MCP without a skill for repeated use. The MCP gives the capability; the skill gives the method.

Summary

MCP is the open standard that connects Claude to tools and data; an MCP server exposes a service’s actions.
Custom connectors (ch. L3.3) are remote MCPs.
You need a custom MCP when no ready connector exists or for internal tools.
In Code: claude mcp add with stdio (local) or http (remote) transport.
Skill + MCP: the MCP gives the capability, the skill the repeatable method.

Next step

In ch. L6.3 — Automations and remote control we’ll see how to make Claude work on its own over time: scheduled tasks, cloud routines, and control from your phone.

Data on MCP and claude mcp add verified on 24/06/2026 against code.claude.com/docs/en/mcp and support.claude.com (custom connector). The commands require Claude Code and an MCP server, so they were not run here.