prefer_pure_methods_over_impure

prefer_pure_methods_over_impure is a cursor rule for Cursor from DeGraciaMathieu/cursor-mdc-rules. It costs 356 tokens per session, scanned A, original, no licence file.

A coding rule that favors pure methods: methods whose results depend only on their inputs and that do not change outside state. Methods with side effects, such as changing shared data, are considered impure.

In plain words
What is it for?
Reviewing method design and identifying places where side effects can be removed or isolated.
Why use it?
Pure methods are easier to test, understand, reuse, and reason about.

Cursor rule for Cursor

Written for Cursor: a Cursor rule (.mdc).

Good fit Reviewing method design and identifying places where side effects can be removed or isolated.

Compare 6 cursor rules from other repositories ↓
Install with agentmods
npx agentmods add rules/degraciamathieu/cursor-mdc-rules/prefer_pure_methods_over_impure
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.

Clone the repo
git clone --depth 1 https://github.com/DeGraciaMathieu/cursor-mdc-rules

Made for: Cursor.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for prefer_pure_methods_over_impure

README.md
[![agentmods](https://agentmods.dev/badge/rules/degraciamathieu/cursor-mdc-rules/prefer_pure_methods_over_impure.svg)](https://agentmods.dev/rules/degraciamathieu/cursor-mdc-rules/prefer_pure_methods_over_impure)
Your own site
<a href="https://agentmods.dev/rules/degraciamathieu/cursor-mdc-rules/prefer_pure_methods_over_impure"><img src="https://agentmods.dev/badge/rules/degraciamathieu/cursor-mdc-rules/prefer_pure_methods_over_impure.svg" alt="Measured on agentmods" height="20"></a>
Per session 356 This file is loaded in full into every session.
When invoked 356 The same file — it is already loaded in full.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
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 5.1 $0.00356 $0.00356
Opus 5 $0.00178 $0.00178
Sonnet 5 $0.00071 $0.00071
Haiku 4.5 $0.00036 $0.00036

Measured 7d ago against content hash 05fa99c49554, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-07, from the pricing page.

Security

Grade A, and why

prefer_pure_methods_over_impure 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 7d 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/prefer_pure_methods_over_impure.mdc · 53 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. 7d ago First seen · 53 lines · 356 tokens per session scan A 05fa99c49554

Subscribe to this mod's changes

prefer_pure_methods_over_impure is a cursor rule published in the GitHub repository DeGraciaMathieu/cursor-mdc-rules (4 stars, last pushed 12mo ago), with no licence file. It adds 356 tokens to every session, about $0.0018 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.