Prompt Harness
Skill: An Operatable Prompt Module
System Prompt defines who the AI is; Tool defines what the AI can do — so what does Skill govern? It governs how to handle a specific situation, step by step. File-as-configuration, version-traceable.
Comparing the Three
System Prompt
Global Identity
Defines who the AI is: name, personality, core principles. It's the backdrop for every conversation.
Tool
Capability Registry
Tells the AI which tools are available: name, parameters, function. It's the menu of capabilities.
Skill
Process Guide
A complete task execution plan: when to trigger, which tools to use, and the step-by-step procedure.
Anatomy of a Skill
Click each block to expand details
content-creator.skill
Trigger Conditions
When to activate this Skill
When the user says trigger phrases like "help me write an article", "I want to write", or "about to write", the AI automatically loads this Skill to guide subsequent behavior. It's not loaded every conversation — only injected when there's a match.
Allowed Tools
Which tools this task may use
Explicitly lists the tools allowed when executing this Skill. For example, content creation may allow web_search and note_read, but not file_delete. Risk is controlled via an allowlist.
Execution Flow
Step-by-step instructions
Describes the full execution steps from start to finish: confirm requirements → gather materials → outline → write section by section → polish → deliver. Each step can have branches and conditional logic.
Output Format Requirements
What the final output should look like
Specifies the format, length, and style of the final output. For example: title under 20 words, clear paragraphs, conversational tone, a call-to-action at the end. Ensures consistent output quality every time.
Skill Lifecycle
1
Author
A single file, plain text
2
Register
Drop into the designated folder to activate
3
Trigger
Auto-loaded when conditions match
4
Iterate
Edit the file = change behavior, Git-traceable
Why not just put it in the System Prompt?
The System Prompt is global — changes affect every scenario. A Skill is loaded on demand, injected only in specific contexts, and won't pollute other tasks' behavior. Plus, Skill files can be version-managed independently: who changed what, and when, is crystal clear.
The System Prompt is global — changes affect every scenario. A Skill is loaded on demand, injected only in specific contexts, and won't pollute other tasks' behavior. Plus, Skill files can be version-managed independently: who changed what, and when, is crystal clear.
Prompts also need to be reusable, iterable, and traceable — Skill is Prompt modularized. Manage AI behavior guidelines like code: one file per task, changes take effect immediately.