python-backend

A set of rules for building Python backends with FastAPI, Django or Flask, which are frameworks for creating web servers and APIs.

In plain words
What is it for?
It is for creating or changing Python web applications, APIs and backend services built with FastAPI, Django or Flask.
Why use it?
It gives an agent backend guidance for these Python frameworks, reducing ambiguity when implementing server-side work.

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/planvault/ai-engineering-playbook/python-backend
Clone the repo
git clone --depth 1 https://github.com/PlanVault/ai-engineering-playbook
Per session 934 This file is loaded in full into every session.
When invoked 934 The same file — it is already loaded in full.
Security scan A 1 finding. Scan, not verified.
Origin unknown 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 $0.00934 $0.00934
Opus 5 $0.00467 $0.00467
Sonnet 5 $0.00187 $0.00187
Haiku 4.5 $0.00093 $0.00093

Measured yesterday against content hash 83369c547599, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

python-backend scanned grade A with 1 finding 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

return requests.get(f"{PAYMENT_API}/orders/{order_id}").json()
example_rules/python-backend.mdc · 91 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

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 · 91 lines · 934 tokens per session scan A 83369c547599

Subscribe to this mod's changes

python-backend is a cursor rule published in the GitHub repository PlanVault/ai-engineering-playbook (4 stars, last pushed 1mo ago), with no licence file. It adds 934 tokens to every session, about $0.0047 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.