design-compare

name	design-compare
description	Compare doc versions across git history. Use when reviewing changes, tracking evolution, or understanding modifications.
allowed-tools	Read, Bash(git *), Bash(diff *), Bash(cat *), Bash(sed *), Bash(grep *)
context	fork
agent	design-doc-agent

Design Documentation Version Comparison

Compares design document versions across git commits, branches, or tags to track evolution and understand changes over time.

Overview

This skill compares document versions by validating git references, loading document content from different versions, performing line-by-line or semantic diffs, analyzing changes for significance, and generating comprehensive comparison reports with metrics and highlights.

Quick Start

Compare with main branch:

/design-docs:design-compare observability.md --ref=main

Compare two commits:

/design-docs:design-compare doc.md --from=abc123 --to=def456

Semantic comparison:

/design-docs:design-compare doc.md --ref=v1.0.0 --format=semantic

Parameters

Required

• doc: Document filename to compare

Optional

• module: Module name (default: inferred from current context)
• ref: Git reference to compare against (commit, branch, tag) (default: main)
• from: Starting git reference for two-point comparison
• to: Ending git reference for two-point comparison
• format: Comparison format - unified, side-by-side, semantic, summary (default: unified)

Workflow

High-level comparison process:

1. Parse parameters to determine document and comparison references
2. Validate references to ensure git refs exist and are accessible
3. Load document versions from current and historical git refs
4. Perform comparison using diff (unified, side-by-side) or semantic analysis
5. Analyze changes to extract metrics and categorize modifications
6. Generate comparison report with summary, frontmatter changes, structural changes, and content diff
7. Highlight significant changes (status changes, completeness jumps, major additions/removals)
8. Format output according to requested format
9. Provide navigation with git commands for further exploration

For detailed implementation steps, see supporting documentation below.

Supporting Documentation

When you need detailed information, load the appropriate supporting file:

For Detailed Workflow

See instructions.md for:

• Complete step-by-step comparison workflow
• Git reference validation methods
• Document version loading from git
• Diff execution (line-by-line, side-by-side, semantic)
• Change analysis and metrics calculation
• Comparison report generation
• Significant change highlighting
• Git navigation commands
• Comparison modes (single ref, two refs, branch, tag)
• Advanced features (whitespace, context, word-level, stats)

Load when: Performing comparisons or need implementation details

For Comparison Formats

See comparison-formats.md for:

• Unified diff format and syntax
• Side-by-side comparison layout
• Semantic diff structure
• Summary format
• Format selection guidelines
• Color coding and highlighting

Load when: Need format specifications or output structure details

For Usage Examples

See examples.md for:

• Compare with main branch
• Compare two commits
• Semantic comparison
• No changes scenario
• Document doesn't exist in reference
• Error scenarios

Load when: User needs examples or clarification

Error Handling

Invalid Git Reference

ERROR: Git reference not found: {ref}

Valid references:
- Commit hash: abc123
- Branch name: main, feature-branch
- Tag name: v1.0.0

Check: git log or git branch -a

Document Not in Repository

ERROR: Document not tracked by git

Document: {doc}

Ensure document is committed before comparing versions.

No Changes Detected

INFO: No changes between versions

Document: {module}/{doc}
References: {from} → {to}

The document is identical in both versions.

Integration

Works well with:

• /design-docs:design-review - Review documents before/after changes
• /design-docs:design-validate - Validate both versions
• /design-docs:design-sync - Understand sync evolution over time
• /design-docs:design-update - See update history

Success Criteria

A successful comparison:

• ✅ Git references validated
• ✅ Document versions loaded from both refs
• ✅ Diff performed successfully
• ✅ Changes analyzed and categorized
• ✅ Metrics calculated accurately
• ✅ Significant changes highlighted
• ✅ Clear comparison report generated
• ✅ Navigation commands provided