python-documentation-standards

A set of rules for writing concise Python docstrings in FastAPI services. It recommends relying on clear names and type hints unless a docstring adds information that the code interface cannot show.

In plain words
What is it for?
Use it when adding or reviewing docstrings, comments, and package documentation under the specified Python source paths. It also guides when to leave package initialization files empty.
Why use it?
Redundant documentation makes code harder to scan and maintain. These rules help keep comments focused on non-obvious behavior, reasons, and important constraints.

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/e-gov/cursor-prompts/python-documentation-standards
Clone the repo
git clone --depth 1 https://github.com/e-gov/cursor-prompts
Per session 833 This file is loaded in full into every session.
When invoked 833 The same file — it is already loaded in full.
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 $0.00833 $0.00833
Opus 5 $0.00417 $0.00417
Sonnet 5 $0.00167 $0.00167
Haiku 4.5 $0.00083 $0.00083

Measured 2d ago against content hash 400e170f4216, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

python-documentation-standards 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 2d ago.

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.

rules/python-fastapi/python-documentation-standards.mdc · 71 lines

How it starts

The opening of the file, as written. The whole thing — 71 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Python Documentation Standards (FastAPI services)

Context

  • Applies under src/** (domain package and core/ starter kit).
  • Default: Rely on clear names and type hints. Docstrings are optional unless they carry information that a reader cannot infer from the API surface.
  • This matches human-maintained style and deslop cleanup: do not add prose that a /deslop pass would strip as redundant.

Default posture (deslop-aligned)

  • Do not add a module docstring that only says what the path or filename already says (e.g. “Book REST routes” on api/books.py).
  • Do not add a class docstring that repeats the class name in sentence form (e.g. “Persisted book entity” on Book).
  • Do not add method docstrings that restate the signature or list obvious steps (“Get book by id” on get_by_id).
  • Do not add Args: / Returns: when parameters and return type are already typed and named well.
  • Leave package __init__.py files empty (no docstring) unless they export a documented public namespace contract.
  • Avoid inline comments that narrate what the next line does; only comment why or non-obvious invariant when necessary.

When a docstring is justified

Add a short docstring (often one line, sometimes + Raises:) only when at least one applies:

  • Non-obvious behavior: ordering guarantees, idempotency, caching, or side effects (e.g. audit emission, extra commits).
  • Non-obvious pre/postconditions or invariants that types cannot express.
  • Raises: when multiple distinct failure modes matter for callers and are not obvious from exception types alone.
  • Security or compliance notes that must stay next to the code (still no secrets or PII in text).
  • Published / reused API consumed by other teams or packages and OpenAPI/Sphinx generation explicitly requires it.

If unsure, omit the docstring and improve naming or types instead.

Anti-patterns (will be removed in deslop-style review)

Read the full file on GitHub · 71 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. 2d ago First seen · 71 lines · 833 tokens per session scan A 400e170f4216

Subscribe to this mod's changes

python-documentation-standards is a cursor rule published in the GitHub repository e-gov/cursor-prompts (34 stars, last pushed 4mo ago), licensed MIT. It adds 833 tokens to every session, about $0.0042 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 2026-08-30.