Agent Customization

Decision Flow

| Primitive | When to Use | |-----------|-------------| | Workspace Instructions | Always-on, applies everywhere in the project | | File Instructions | Explicit via applyTo patterns, or on-demand via description | | MCP | Integrates external systems, APIs, or data | | Custom Agents | Subagents for context isolation, or multi-stage workflows with tool restrictions | | Prompts | Single focused task with parameterized inputs | | Skills | On-demand workflow with bundled assets (scripts/templates) |

Quick Reference

Consult the reference docs for templates, domain examples, advanced frontmatter options, asset organization, anti-patterns, and creation checklists.

| Type | File | Location | Key Field | Reference | |------|------|----------|-----------|---------| | Workspace Instructions | copilot-instructions.md, AGENTS.md | .github/ or root | N/A (always applies) | Link | | File Instructions | *.instructions.md | .github/instructions/ | applyTo (explicit), description (on-demand) | Link | | Prompts | *.prompt.md | .github/prompts/ | description (user-invoked) | Link | | Custom Agents | *.agent.md | .github/agents/ | description (on-demand), infer (subagent) | Link | | Skills | SKILL.md | .github/skills/<name>/ | description (on-demand) | Link |

User-level: {{USER_PROMPTS_FOLDER}}/ (.prompt.md, .instructions.md, .agent.md; not skills) Customizations roam with user's settings sync

Creation Process

If you need to explore or validate patterns in the codebase, use a read-only subagent. If the ask-questions tool is available, use it to interview the user and clarify requirements.

Follow these steps when creating any customization file.

1. Determine Scope

Ask the user where they want the customization:

• Workspace: For project-specific, team-shared customizations → .github/ folder
• User profile: For personal, cross-workspace customizations → {{USER_PROMPTS_FOLDER}}/

2. Choose the Right Primitive

Use the Decision Flow above to select the appropriate file type based on the user's need.

3. Create the File

Create the file directly at the appropriate path:

• Use the location tables in each reference file
• Include required frontmatter as needed
• Add the body content following the templates

4. Validate

After creating:

• Confirm the file is in the correct location
• Verify frontmatter syntax (YAML between --- markers)
• Check that description is present and meaningful

Edge Cases

Instructions vs Skill? Does this apply to most work, or specific tasks? Most → Instructions. Specific → Skill.

Skill vs Prompt? Multi-step workflow with bundled assets → Skill. Single focused task with inputs → Prompt.

Skill vs Custom Agent? Same capabilities for all steps → Skill. Need context isolation (subagent returns single output) or different tool restrictions per stage → Custom Agent.