COP-014: Prompt File Unknown Frontmatter Field

Summary

• Rule ID: COP-014
• Severity: MEDIUM
• Category: GitHub Copilot
• Normative Level: SHOULD
• Auto-Fix: Yes (safe)
• Verified On: 2026-04-22

Applicability

• Tool: github-copilot
• Version Range: unspecified
• Spec Revision: unspecified

Evidence Sources

• https://code.visualstudio.com/docs/copilot/customization/prompt-files
• https://docs.github.com/en/copilot/reference/custom-instructions-support

Test Coverage Metadata

• Unit tests: true
• Fixture tests: true
• E2E tests: false

Examples

The following examples demonstrate what triggers this rule and how to fix it.

Invalid

---
description: Refactor selected code
unknown-option: true
---
Refactor the selected code.

Valid

---
description: Refactor selected code
agent: ask
---
Refactor the selected code.