COP-004: Unknown Frontmatter Keys - GitHub Copilot

Summary

• Rule ID: COP-004
• 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://docs.github.com/en/copilot/how-tos/custom-instructions/adding-repository-custom-instructions-for-github-copilot
• 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

---
applyTo: "**/*.ts"
unknownKey: some-value
---
# TypeScript Instructions

Use strict mode.

Valid

---
applyTo: "**/*.ts"
---
# TypeScript Instructions

Use strict mode.