fission-ai__openspec/openspec/changes/archive/2025-08-13-add-diff-command/proposal.md

Add Diff Command to OpenSpec CLI

Why

Developers need to easily view differences between proposed spec changes and current specs without manually comparing files.

What Changes

• Add openspec diff [change-name] command that shows differences between change specs and current specs
• Compare files in changes/[change-name]/specs/ with corresponding files in specs/
• Display unified diff output showing added/removed/modified lines
• Support colored output for better readability

Impact

• Affected specs: New capability cli-diff will be added
• Affected code:
  • src/cli/index.ts - Add diff command
  • src/core/diff.ts - New file with diff logic (~80 lines)