Prompt vs Skill vs Tool
Prompt
A well-written one-off request.
Skill
A fixed repeatable procedure with inputs and validation.
Tool/MCP
A real read/write action against external systems.
SKILL.md Example
SKILL.md
# Project Release Skill
## When to use
- When the user asks "prepare a release"
## Inputs
- branch name
- target environment
- release notes draft
## Procedure
1. Check change scope with git status
2. Run build/test commands
3. Check migrations and env changes
4. Update release notes
5. Record Go/No-Go decision
## Validation
- npm run build
- npm testDesign Checks
- Is the trigger condition clear?
- Is the file/system scope narrow enough?
- Are success criteria and recovery steps documented?
- If tool calls are needed, are permissions and approvals clear?