Short answers first. For the deeper taxonomy, read Skills vs tools vs MCP. For the file format, read Anatomy of a skill.
What are agent skills?
Agent skills are reusable capability packages for AI agents. The open format centers on a SKILL.md file with metadata and instructions, plus optional scripts, references, and assets.
Are skills the same as prompts?
No. A prompt is one piece of instruction text in a context. A skill is a durable, installable folder that can be discovered, activated, and supported by files or scripts.
Are skills the same as MCP?
No. MCP is a protocol for connecting AI applications to external systems. Skills are a packaging format for reusable agent procedure. They complement each other.
Can a skill run code?
A skill can include scripts, but whether those scripts run depends on the agent client, sandbox, permissions, and user approval model.
What belongs in SKILL.md?
Put the always-needed workflow, trigger guidance, constraints, validation steps, and pointers to supporting files in SKILL.md. Move long details into references and exact repeatable operations into scripts.
How portable are skills today?
The open directory shape is portable, but runtime behavior varies. Portability depends on client support, file locations, script permissions, dependencies, packaging, and tool availability.
Do skills replace tools?
No. Tools execute actions. Skills teach the agent how to perform a workflow, including which tools or scripts to use and how to validate the result.
Where should I start?
Start with one repeated workflow the agent performs inconsistently. Write a precise description, a short SKILL.md workflow, and two or three realistic test prompts.