Summary
In late July 2026, GitHub introduced custom agents for the Copilot CLI: developers define an agent in a Markdown file stored in a repository's .github/agents directory (or ~/.copilot/agents), specifying its role, the tools it may use, the standards it should follow, and the outputs it should produce. This turns one-off prompts into reusable, version-controlled agent workflows that live alongside the code and travel with the repo.
What changed
GitHub Copilot CLI gained custom-agent support driven by Markdown definition files (e.g. .github/agents/security-auditor.agent.md), letting teams declare reusable agents with scoped tools and guardrails in-repo.
Why it matters
Storing agent definitions as committed Markdown makes agent behavior reviewable, shareable, and reproducible across a team the same way CI config is, and it converges with the emerging AGENTS.md convention. It shifts Copilot from an interactive assistant toward a configurable, guardrailed automation surface that fits existing code-review and governance practices.
Evidence excerpt
A custom agent is a Copilot agent defined using a Markdown file where you describe how the agent should operate, what tools it can use, what standards it should follow, and what outputs it should produce; files live in .github/agents/ or ~/.copilot/agents/.