Guide
Skill vs MCP vs Plugin — which do you actually need?
Three primitives, three jobs. Most teams use all three. Here is the simplest mental model that survives in production.
The one-line answer
Three primitives
Skill
Changes how the agent thinks. Methodology, workflows, voice, branded patterns. SKILL.md + optional scripts.
MCP server
Changes what the agent can do. Connects the agent to tools and data — DB, APIs, filesystem.
Plugin
Bundles Skills + MCP + commands. Packaging for one-line install across repos and teams.
Decision tree
Pick the right primitive
- Q1. Does the agent already have access to the data and tools it needs? → If no, build an MCP server.
- Q2. Is the agent already capable of the task but doing it inconsistently or to a low standard? → Build a Skill.
- Q3. Are you shipping a coordinated bundle of the above to a team or marketplace? → Wrap it in a Plugin.
Examples
Concrete pairs
| Goal | Skill | MCP |
|---|---|---|
| Generate distinctive UIs | frontend-design | — (none required) |
| Query your Postgres DB | planetscale-skills (or your team's schema patterns) | postgres MCP server |
| Run a security audit | trail-of-bits | filesystem MCP for source access |
| Take action across SaaS apps | composio (skill) | composio (MCP — pairs with the skill) |
FAQ
Common questions
When should I build a Skill?
Build a Skill when you want the agent to know how to do something — methodology, voice, branded patterns, team workflows. Skills change how the agent thinks.
When should I build an MCP server?
Build an MCP server when the agent needs to access something it cannot reach — your database, an internal API, a SaaS that has no integration. MCPs change what the agent can do.
When should I build a Plugin?
Bundle Skills + MCP servers + commands as a Plugin when you want a one-line install for a coordinated set. Plugins are packaging, not a third primitive.
Can a Skill use an MCP server?
Yes — many Skills assume one or more MCPs are available. The Skill provides the methodology; the MCP provides the connectivity.
Looking for the full directory? Start with trending Skills or editorial collections.