Cqrs Implementation

When to use this skill

Use Cqrs Implementation when an AI agent needs a reusable SKILL.md workflow for this job: Implement Command Query Responsibility Segregation for scalable architectures. Use when separating read and write models, optimizing query performance, or building event-sourced systems.

When not to use it

Skip Cqrs Implementation when the task is outside the coding category, or when a more specific skill in this directory already covers the same workflow with clearer triggers.

How to install

1. Personal install: create ~/.claude/skills/cqrs-implementation/SKILL.md (and any bundled scripts) so Claude Code, Claude Desktop, and compatible agents can load it in every project.
2. Project install: commit the same folder at .claude/skills/cqrs-implementation/ so teammates get the skill with the repo.
3. Restart the agent session after copying files so it re-scans the skills directory, then ask for the task in words that match the skill description.

Full install guide for Claude, Cursor, and Codex

What this skill does

# CQRS Implementation

Comprehensive guide to implementing CQRS (Command Query Responsibility Segregation) patterns.

## When to Use This Skill

- Separating read and write concerns - Scaling reads independently from writes - Building event-sourced systems - Optimizing complex query scenarios - Different read/write data models needed - High-performance reporting requirements

## Core Concepts

### 1. CQRS Architecture

``` ┌─────────────┐ │ Client │ └──────┬──────┘ │ ┌────────────┴────────────┐ │ │ ▼ ▼ ┌─────────────┐ ┌─────────────┐ │ Commands │ │ Queries │ │ API │ │ API │ └──────┬──────┘ └──────┬──────┘ │ │ ▼ ▼ ┌─────────────┐ ┌─────────────┐ │ Command │ │ Query │ │ Handlers │ │ Handlers │ └──────┬──────┘ └──────┬──────┘ │ │ ▼ ▼ ┌─────────────┐ ┌─────────────┐ │ Write │─────────►│ Read │ │ Model │ Events │ Model │ └─────────────┘ └─────────────┘ ```

### 2. Key Components

| Component | Responsibility | | ------------------- | ------------------------------- | | **Command** | Intent to change state | | **Command Handler** | Validates and executes commands | | **Event** | Record of state change | | **Query** | Request for data | | **Query Handler** | Retrieves data from read model | | **Projector** | Updates read model from events |

## Templates and detailed worked examples

Full template library and detailed worked examples live in `references/details.md`. Read that file when you need the concrete templates.

## Best Practices

### Do's

- **Separate command and query models** - Different needs - **Use eventual consistency** - Accept propagation delay - **Validate in command handlers** - Before state change - **Denormalize read models** - Optimize for queries - **Version your events** - For schema evolution

### Don'ts

- **Don't query in commands** - Use only for writes - **Don't couple read/write schemas** - Independent evolution - **Don't over-engineer** - Start simple - **Don't ignore consistency SLAs** - Define acceptable lag

Intended uses

• Separating read and write concerns
• Scaling reads independently from writes
• Building event-sourced systems
• Optimizing complex query scenarios
• Different read/write data models needed
• High-performance reporting requirements