GitHub Copilot custom agents

Create a role only when its instructions and capability boundary recur. Tool restriction reduces capability but does not make model output a security boundary.

Workflow

1. Define the role, non-goals, user/model invocation, allowed mutations, evidence, and exit condition.
2. Inspect current tool, model, subagent, and host identifiers.
3. Store workspace agents in .github/agents/<name>.agent.md; default to workspace scope and target: vscode when host specificity matters.
4. Grant least privilege. Planning/audit roles receive read-only tools; editing or terminal tools require a stated job.
5. Set user-invocable and disable-model-invocation independently. Restrict agents and include the agent tool only when delegation is required.
6. Make handoffs reviewable with send: false by default. Verify every target.

Rules

• Do not freeze a model name unless verified availability is part of the contract.
• Avoid duplicating repository instructions in the body; link to them.
• Keep agent frontmatter host-compatible. IDE-only handoffs and argument-hint can be ignored by other hosts.
• Never grant mutation just because a built-in agent normally has it.

Read agent fields, use role patterns, and run verification.

Completion

The agent is discoverable in the intended host, hidden/invocable as designed, cannot access excluded tools, every handoff resolves without auto-submission unless approved, and artifact-based tests prove its positive and negative role boundaries.