Backend Master Agent

Encodes expert backend development knowledge -- API design, database patterns, authentication, error handling, and the discipline of type-safe, tested,...


Level	L1 Vibe Coder
Category	Agent Roles

What It Provides

The Backend Master skill equips agents with comprehensive server-side development expertise spanning multiple languages (Python, Node.js, Go, Rust), frameworks (FastAPI, Django, Express, NestJS, Gin, Axum), databases (PostgreSQL, MongoDB, Redis), and API paradigms (REST, GraphQL, WebSockets, gRPC). It teaches agents to implement robust backend code that follows the architecture designed by the Lead Architect.

Without this skill, agents write backend code with incomplete error handling, missing type hints, bare exception clauses, and insufficient test coverage. With it, agents follow a nine-step implementation workflow (review spec, implement domain, create repository, implement use case, write unit tests, create API endpoint, write integration tests, add documentation, update state) and adhere to strict quality standards.

The skill emphasizes the handoff protocol: Backend Master receives architecture specifications from Lead Architect and produces tested, documented implementations that QA Sentinel can verify independently.

When It Activates

When implementing API endpoints, database models, or business logic
When writing backend tests (unit, integration, API endpoint tests)
When selecting database strategies, ORM configurations, or authentication approaches
When an agent needs to implement a use case from an architectural specification

The Knowledge Inside

Implementation Workflow

The nine-step workflow ensures nothing is skipped. Review the architecture specification first. Implement domain entities and value objects. Create the repository implementation. Implement the use case logic with proper error handling. Write unit tests for the use case (minimum 85% coverage). Create the API endpoint with validation. Write integration tests. Add OpenAPI/Swagger documentation. Update project state with progress.

Quality Standards

Six non-negotiable quality requirements: type hints on all function signatures, error handling with specific exceptions (never bare except), async/await for all I/O operations, test coverage at or above 85%, API documentation via OpenAPI/Swagger, and p95 response time under 200ms. The skill provides concrete code examples showing the contrast between good patterns (full type hints, specific error types) and bad patterns (no types, bare except, returning None on error).

Database Selection Framework

A decision framework for choosing the right database: PostgreSQL when complex queries and ACID transactions are needed, MongoDB when flexible schemas and document-oriented data fit the model, Redis when caching, session storage, or real-time features are the priority. Agents learn to match database choice to the actual data access patterns rather than defaulting to a familiar option.

Authentication and Security

The skill covers JWT tokens, OAuth 2.0/OpenID Connect, session-based authentication, password hashing (bcrypt, argon2), API key management, and rate limiting. Agents learn which authentication approach fits which scenario and how to implement it securely.

How to Leverage It

Provide the agent with an architectural specification or describe the API endpoint you need. The agent will follow the nine-step workflow and produce implementation with tests and documentation.

Example: User Registration Endpoint

User: "Implement user registration with email verification"
What happens: The agent creates the User entity with Email value object,
implements RegisterUserUseCase with proper validation, creates the
repository implementation, writes the POST /users/register endpoint with
request validation, generates unit and integration tests, and adds
OpenAPI documentation.

Power Applications

Use the handoff protocol to pipeline work: architect designs, backend implements, QA verifies -- all with clear contracts
Apply the database selection framework before every new data model to avoid costly migration later
Enforce the quality standards as CI gate criteria to prevent quality regression

Skill	Relationship
agent-lead-architect	Provides the architectural specifications that Backend Master implements
agent-qa-sentinel	Receives implementations from Backend Master for quality verification
agent-integration-specialist	Collaborates on external API adapter implementations
optimization	Backend Master applies optimization patterns for database and API performance

Tips

Never use bare except clauses -- always catch specific exception types and handle them appropriately
Write tests alongside implementation, not as an afterthought; the nine-step workflow interleaves them deliberately
Type hints are not optional; they serve as both documentation and static analysis input