Design Principles

1. Convention Over Configuration

• Standard directory structure (.specify/extensions/\{name\}/)
• Declarative manifest (extension.yml)
• Predictable command naming (speckit.\{extension\}.\{command\})

2. Fail-Safe Defaults

• Missing extensions gracefully degrade (skip hooks)
• Invalid extensions warn but don't break core functionality
• Extension failures isolated from core operations

3. Backward Compatibility

• Core commands remain unchanged
• Extensions additive only (no core modifications)
• Old projects work without extensions

4. Developer Experience

• Simple installation: specify extension add jira
• Clear error messages for compatibility issues
• Local development mode for testing extensions

5. Security First

• Extensions run in same context as AI agent (trust boundary)
• Manifest validation prevents malicious code
• Verify signatures for official extensions (future)