What differentiates on Custom Agents, Agent Skills and Custom Instructions in Copilot CLI

[ans-4175]

Select Topic Area

General

Copilot Feature Area

General

Body

Hi, I’m experimenting with GitHub Copilot CLI and am a bit confused about when to use Custom Agents, Agent Skills, and Custom Instructions, especially for real-world workflows in a codebase.

From the docs, my current understanding is roughly:

Custom agents: specialized versions of Copilot coding agent that you configure as “profiles” for particular workflows, conventions, tools, etc., and then explicitly select (for example via /agent in Copilot CLI or choosing the agent in the UI). They feel like opinionated, persistent teammates that can own an end‑to‑end workflow for a repo or organization.
​

Agent Skills: folders under .github/skills (or .claude/skills) that package instructions + scripts + examples for specific, reusable capabilities (e.g., “webapp-testing”, “github-actions-failure-debugging”). Copilot decides when to load a skill based on its description and my prompt, and the same skill can be reused across Copilot CLI, Copilot coding agent, and VS Code.
​

Repository custom instructions (.github/copilot-instructions.md): always‑on background guidance that sets project‑wide norms (architecture notes, coding standards, how to build/test/deploy, etc.), which Copilot should generally follow for any task in that repo.
​

What is not clear to me is how GitHub envisions these three working together in practice, especially with Copilot CLI:

For something like “diagnose and fix failing GitHub Actions workflows in this monorepo,” should that primarily be:

a custom agent configured for CI/debugging,
one or more Agent Skills (e.g., github-actions-failure-debugging plus repo‑specific skills),

or mostly handled via repository custom instructions with only light use of skills/agents?

Are there recommended rules of thumb such as:

• “Use custom instructions for stable, repo‑wide conventions”
• “Use Agent Skills for portable, task‑specific capabilities”
• “Use custom agents when you want a named persona that consistently orchestrates tools/skills for a workflow”?

In Copilot CLI specifically, are there examples or best practices of how people structure:

one or two general‑purpose custom agents that then rely heavily on skills, versus many narrow custom agents, versus mostly skills + repo instructions and minimal use of custom agents?

Concrete scenarios or patterns used by the Copilot team or other users would be really helpful

Thanks in advance for any clarification or design guidance on how to choose between these options and combine them effectively.