fastapi_project_structure_guide

A recommended folder layout for FastAPI applications, which are Python web backends, with sections for a frontend, documentation, scripts, data, logs, and configuration. It is tailored to applications using LangChain, vector databases, and agent-based systems.

In plain words
What is it for?
Use it when starting or reorganizing a FastAPI project that connects a web interface to AI features, stored documents, or automated agents.
Why use it?
It gives related code and project files predictable places, making a growing application easier to navigate and maintain.

Cursor rule

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add rules/jondoescoding/jondoescoding-coding-rules/fastapi_project_structure_guide
Clone the repo
git clone --depth 1 https://github.com/jondoescoding/jondoescoding-coding-rules
Per session 13 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,389 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00013 $0.01389
Opus 5 $0.00006 $0.00694
Sonnet 5 $0.00003 $0.00278
Haiku 4.5 $0.00001 $0.00139

Measured yesterday against content hash 0ed7a226e548, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

fastapi_project_structure_guide scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

templates/cursor-rules/python/fast-api/fastapi_project_structure_guide.mdc · 194 lines

How it starts

The opening of the file, as written. The whole thing — 194 lines — stays where its author put it; the contents beside it link to each section on GitHub.

FastAPI Project Structure Guide

This rule provides a comprehensive outline of a well-organized FastAPI project structure optimized for AI-powered applications with LangChain integration, vector databases, and agent-based architectures.

📁 Project Root Structure

project-root/
├── backend/                    # FastAPI backend application
├── frontend/                   # Frontend application (Next.js/React)
├── docs/                      # Project documentation
├── scripts/                   # Deployment and utility scripts
├── .env                       # Environment variables
├── .gitignore                 # Git ignore patterns
├── LICENSE                    # Project license
└── README.md                  # Project overview

🚀 Backend Structure (backend/)

Core Application Files

backend/
├── src/                       # Main source code directory
├── data/                      # Data files, CSVs, documents
├── docs/                      # Backend-specific documentation
├── logs/                      # Application logs
├── scripts/                   # Backend utility scripts
├── pyproject.toml            # Python project configuration
├── requirements.txt          # Python dependencies
├── README.md                 # Backend documentation
└── start.sh                  # Application startup script

Source Code Organization (backend/src/)

📋 Main Entry Point
  • main.py - FastAPI application initialization
    • App configuration and metadata
    • CORS middleware setup
    • Router registration
    • Environment-based configuration
    • Lifespan event handlers
🌐 API Layer (api/)

API route definitions and endpoint handlers:

  • {feature}_api.py - Feature-specific API routers
    • Request/response models validation
    • Error handling and logging
    • Business logic delegation to services
    • OpenAPI documentation

Example structure:

# pdf_agent_api.py
from fastapi import APIRouter, HTTPException
from ..models.chatbot import RagChatRequest, ChatResponse
from ..services.pdf_agent_service import run_retrieval_agent

router = APIRouter()

@router.post("/pdf_agent", response_model=ChatResponse)
async def rag_agent_endpoint(chat_request_body: RagChatRequest):
    # Endpoint implementation

Read the full file on GitHub · 194 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 194 lines · 13 tokens per session scan A 0ed7a226e548

Subscribe to this mod's changes

fastapi_project_structure_guide is a cursor rule published in the GitHub repository jondoescoding/jondoescoding-coding-rules (2 stars, last pushed 1mo ago), licensed MIT. It adds 13 tokens to every session and 1,389 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.