Skills vs MCP tools vs prompts: how AI capabilities get sold today

"Prompt," "skill," and "MCP tool" get used interchangeably, but they're different products with different economics. If you're deciding what to build or sell, here's the map — including the structural problem almost all of them share.

Prompts: the simplest unit

A prompt is a block of instructions you paste into a chat model. It's the easiest AI capability to create and the easiest to sell — prompt marketplaces have existed for years, typically charging a few dollars per prompt as a one-time download.

It's also the easiest to lose. A prompt's entire substance is visible text; the buyer receives it, owns it, and can share or resell it instantly. Prompt sellers invented the complaint this site exists to answer: one sale, infinite copies.

Skills: prompts that grew up

A skill — in the sense agent platforms use the word, often a SKILL.md file — is a structured, reusable method an AI agent can load and follow: instructions, steps, conventions, sometimes scripts and reference material. Where a prompt is a one-shot incantation, a skill is closer to a standard operating procedure for an agent.

Skills are more valuable than prompts because they encode more refinement: edge-case handling, ordering, judgment. And the existing distribution model is the same as prompts — marketplaces and registries deliver the skill file itself to the buyer's machine. More refinement in the file means more IP in the file, which means a worse version of the same leak.

MCP tools: capabilities behind an interface

MCP (Model Context Protocol) is the open standard that lets AI agents call external tools — a tool server exposes functions, and the agent invokes them over the protocol. An MCP tool is genuinely different from a prompt or skill file: if the server is hosted, the buyer's agent only sees the tool's interface, not its implementation.

That's real protection — but MCP tools are software products. Building one means writing and operating a server: code, hosting, auth, uptime. The protection comes from being a developer with infrastructure, not from the marketplace. For the far larger population of people whose expertise lives in language — methods, checklists, judgment encoded as instructions — "just build and host an MCP server" isn't an answer. And many self-hosted or downloadable MCP servers ship their source anyway, landing back at the leak.

The pattern across all three

• Prompts: trivially copyable; one-time sale; IP ships to the buyer.
• Skills: more valuable, equally copyable; one-time sale; IP ships to the buyer.
• MCP tools: protectable, but only if you can build and run server software yourself.

The gap in the market is the obvious combination: skills written in plain language, delivered like a hosted tool. The seller uploads the skill once; it runs server-side; the buyer's agent calls it and gets results, not the file; the seller earns per call without ever operating a server.

Which should you sell?

If you can code and want to operate a product, an MCP tool gives you the most control. If your edge is expertise you can write down — a method, a process, a way of judging work — a skill is the natural form, and the thing to be careful about is distribution: a skill sold as a download is a prompt-marketplace product with prompt-marketplace economics. Before listing anywhere, run your skill through the doing-vs-dispensing test to know what's protectable at all.