I have been learning about skills, sub agents, mcp and plugins for a few months, and if I am honest, most explanations didn't resonate with me. They either felt too technical or they all blurred into the same thing. Tools, capabilities, agents. It all started to sound the same after a while. I remember reading through documentation more than once and still not being able to clearly explain the difference to myself. I needed a way to visualise it as I find that's a far better way of remembering. For me anyway.
Imagine You Are Directing a Film
You are the director. Your job is to get a scene done. You know what outcome you want, but you are not doing everything yourself. You rely on different kinds of support to make it happen.
Skills
A skill is like pulling out a page of the script. It tells you how something should play out. The structure, the steps, the flow. But it does not actually do anything on its own. You are not memorising the whole script either. You just grab the part you need when you need it. That was the shift for me. Skills are not ability. They are guidance.
Sub Agents
Sub agents are like actors you bring in to perform a role. You do not walk them through every single step. You give them a goal, and they take it from there using their own experience. A good actor does not just follow instructions. They interpret, adapt, and deliver something that works. That is what sub agents are doing. They are not just following steps. They are handling the task for you.
MCP
MCP is the prop department. This one felt the most abstract at first. If you need a prop, a costume, or some specific piece of equipment, you do not already have it sitting there. You ask for it and someone brings it to the set. But it is not just fetching things. The prop department can also make things happen on set. Like returning a hire, placing an order, or getting a message to another part of the production. MCP works the same way. It is not just connecting you to data. It can also take actions in external systems, like creating a record, sending a message, or updating something in a tool you use. It is not doing the thinking. It is not making decisions. But it can reach out and act on your behalf.
Plugins
Plugins are the permanent fixtures on set. The overhead lighting, the built-in sound system, the things that are already there when you arrive. You do not bring them in like MCP. You do not hire them like a sub agent. They are just part of the setup, ready to use when the job calls for them. The key difference is that plugins are static. They do one thing and they do it well. MCP is dynamic, you reach out and pull something in when you need it. Plugins are already there waiting.
The Simple Way I Remember It
Skills tell you how to do something.
Sub agents do it for you.
MCP brings in what you do not have, and can act on your behalf.
Plugins give you a tool to use directly.
When Would You Use Each One
This was the part that helped me the most in practice. Use a skill when you are not sure how to approach something and need guidance or structure. Use a sub agent when the task is complex or you want something handled without micromanaging every step. Use MCP when you need access to something external, like data, systems, or resources that are not already available. Or when you need to take an action in an external system, like creating a record or sending a message. And it is worth knowing that a sub agent can use MCP to do its job. They are not either/or. They stack. Use a plugin when there is a specific tool that can do the job more directly or efficiently. They can all help you get to the same end result, but they do it in very different ways.