name: Local-First Patterns Analysis description: This skill should be used when the user asks to "analyze local-first patterns", "review offline support", "check sync implementation", "audit conflict resolution", "review optimistic updates", "check offline capabilities", or mentions local-first architecture, CRDTs, offline-first, sync patterns, or data synchronization. version: 1.0.0

Local-First Patterns Analysis Framework

Use this framework when analyzing a codebase for local-first architecture quality. Focus on offline capabilities, sync reliability, and conflict handling.

Analysis Criteria

1. Offline Data Storage

What to check:

• Local persistence mechanism (IndexedDB, SQLite, localStorage)
• Data schema and structure for offline use
• Storage capacity management
• Data encryption at rest

Storage options to identify:

• IndexedDB: Complex data, large datasets
• localStorage: Simple key-value, small data
• SQLite (via libraries): Relational data
• OPFS: File system access
• Cache API: Request/response caching

Warning signs:

• Over-reliance on localStorage for complex data
• No storage quota management
• Missing data migration strategy
• Unencrypted sensitive local data

2. Sync Architecture

What to check:

• Sync protocol and mechanism
• Sync direction (one-way, two-way, multi-master)
• Sync granularity (document, field, operation)
• Sync frequency and triggers

Common patterns:

• Last-write-wins: Simple but can lose data
• Operational transforms: Real-time collaboration
• CRDTs: Conflict-free by design
• Event sourcing: Full history, replayable
• Delta sync: Only changed data

What to look for:

// Sync trigger patterns
- On reconnect
- Periodic background sync
- On user action
- Real-time via WebSocket
- Push notification triggered

3. Conflict Resolution

What to check:

• Conflict detection mechanism
• Resolution strategy (automatic vs manual)
• User notification of conflicts
• Conflict history/audit trail

Resolution strategies:

• Automatic merge: Field-level, non-conflicting changes merge
• Last-write-wins: Timestamp-based, may lose data
• First-write-wins: Preserves original, may reject valid changes
• Custom merge: Domain-specific logic
• User resolution: Present conflicts for manual resolution
• CRDT-based: Mathematically conflict-free

Warning signs:

• No conflict detection
• Silent data loss on conflict
• No way to recover from bad merge
• Inconsistent resolution across data types

4. Optimistic Updates

What to check:

• UI updates before server confirmation
• Rollback mechanism on failure
• Pending state indication to users
• Queue management for offline changes

Good patterns:

// Optimistic update with rollback
async function updateItem(item) {
  const previousState = store.get(item.id);
  store.update(item); // Optimistic

  try {
    await api.update(item);
  } catch (error) {
    store.set(item.id, previousState); // Rollback
    notifyUser('Update failed, changes reverted');
  }
}

Warning signs:

• No rollback on failure
• User not informed of pending state
• Lost updates when offline
• No retry for failed operations

5. Network State Management

What to check:

• Online/offline detection
• Connection quality awareness
• Graceful degradation
• Reconnection handling

What to look for:

• navigator.onLine usage
• Network event listeners
• Connection quality indicators
• Offline mode UI changes

6. Data Versioning and Migrations

What to check:

• Schema version tracking
• Migration strategy for local data
• Backwards compatibility
• Data integrity during migrations

7. Sync Queue and Retry

What to check:

• Offline operation queue
• Retry logic with backoff
• Queue persistence across sessions
• Operation ordering guarantees
• Idempotency of queued operations

Good patterns:

// Persistent queue with retry
const syncQueue = {
  operations: persistentStore.get('syncQueue') || [],

  add(operation) {
    operation.id = generateId();
    operation.timestamp = Date.now();
    this.operations.push(operation);
    this.persist();
  },

  async processQueue() {
    for (const op of this.operations) {
      try {
        await this.executeWithRetry(op);
        this.remove(op.id);
      } catch (e) {
        if (!isRetryable(e)) this.markFailed(op.id);
      }
    }
  },
};

8. Real-Time Collaboration (if applicable)

What to check:

• Presence awareness
• Cursor/selection sharing
• Live updates propagation
• Conflict handling during collaboration

Technologies to identify:

• WebSocket connections
• Yjs, Automerge, or similar CRDTs
• Operational transformation libraries
• Presence channels

Report Structure

# Local-First Analysis Report

## Summary

[Overall local-first maturity assessment]

## Capabilities Assessment

| Capability          | Status         | Notes     |
| ------------------- | -------------- | --------- |
| Offline Storage     | Yes/Partial/No | [Details] |
| Offline Mutations   | Yes/Partial/No | [Details] |
| Sync Mechanism      | [Type]         | [Details] |
| Conflict Resolution | [Strategy]     | [Details] |
| Optimistic Updates  | Yes/Partial/No | [Details] |

## Architecture Overview

[How data flows between local and remote]

## Strengths

[Good local-first patterns found]

## Issues Found

### Critical

[Issues causing data loss or corruption]

### Improvements Needed

[Gaps in offline support]

## Recommendations

### Essential

[Must-have improvements for reliable offline]

### Enhancements

[Nice-to-have improvements]

## Sync Flow Diagram

[Visual representation of sync architecture]

Analysis Process

1. Identify storage layer: Find local persistence mechanisms
2. Map sync architecture: Understand how data flows to/from server
3. Trace offline scenarios: What happens when connection is lost
4. Evaluate conflict handling: How are concurrent edits resolved
5. Check optimistic updates: Does UI respond immediately
6. Review network handling: How is online/offline state managed
7. Test edge cases: Consider what happens in failure scenarios
8. Document findings: Create improvement roadmap