fastapi-backend-guidelines

Build FastAPI backends with Domain-Driven Design and a Router-Service-Repository pattern.

2|1|Updated Mar 1, 2026

Search Tags:#architecture #fastapi #ddd #async #error-handling #dto #repository-pattern

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npx skills add https://github.com/junDevCodes/Claude-Harness --skill fastapi-backend-guidelines-jundevcodes

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Please help me install this Agent Skill.
Skill: fastapi-backend-guidelines
Source: https://github.com/junDevCodes/Claude-Harness/tree/main/.claude/skills/fastapi-backend-guidelines
Command: npx skills add https://github.com/junDevCodes/Claude-Harness --skill fastapi-backend-guidelines-jundevcodes

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

This skill provides a structured blueprint for building FastAPI backends using Layered Architecture and Domain-Driven Design, helping teams enforce clean boundaries, consistent DTO usage, and robust error handling.

Core Features & Use Cases

Layered Architecture: Router → Service → Repository pattern to separate concerns.
Async Best Practices: All I/O operations are async with proper session management.
DDD & DTOs: Domain-driven structure with Pydantic DTOs and validation.
Error Handling: Centralized domain exceptions and HTTP mappings.

Quick Start

Follow this guideline to structure new FastAPI domains with layered architecture, DTO validation, and robust error handling.

Frequently Asked Questions about fastapi-backend-guidelines

High-intent search queries and answers about installing and using this skill.

FAQPage Schema

How do I structure a FastAPI backend using Domain-Driven Design and layered architecture?▼

A FastAPI backend using Domain-Driven Design separates concerns into Router, Service, and Repository layers. This enforces clean boundaries, consistent DTO usage, and robust error handling for scalable apps.

What is the best way to manage async database sessions in a FastAPI repository pattern?▼

Manage async database sessions in a FastAPI repository pattern by using async/await for all I/O operations with proper session management. The blueprint enforces read and write session separation to maintain clean data boundaries.

How does centralized error handling work with FastAPI domain exceptions?▼

Centralized error handling in FastAPI works by mapping domain exceptions to HTTP responses. This approach captures errors consistently across the Service and Repository layers, providing robust API error management.

How do I validate FastAPI request data using Pydantic DTOs?▼

Validate FastAPI request data using Pydantic DTOs to enforce domain-driven structure and validation rules. DTOs act as Data Transfer Objects that separate internal domain models from external API contracts.

Can I use ULID IDs instead of standard UUIDs in FastAPI ORM models?▼

Yes, you can use ULID IDs instead of standard UUIDs in FastAPI ORM models. This architectural blueprint enforces ULID usage for primary keys to ensure sortable and unique identifiers across your database.

When should I separate read and write sessions in a FastAPI application?▼

Separate read and write sessions in a FastAPI application when building scalable apps with a layered Router-Service-Repository pattern. This separation optimizes database concurrency and enforces strict data consistency boundaries.