fortran

A set of modern Fortran guidelines for scientific and numerical programs, covering modules, data types, memory safety, and testing.

In plain words
What is it for?
Use it when writing or reviewing Fortran modules, numerical algorithms, scientific simulations, and their tests.
Why use it?
It helps prevent unclear interfaces, unsafe memory use, obsolete language patterns, and mistakes with numerical precision or physical units.

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/patrickjs/awesome-cursorrules/fortran
Clone the repo
git clone --depth 1 https://github.com/PatrickJS/awesome-cursorrules
Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 631 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 $0.00000 $0.00631
Opus 5 $0.00000 $0.00316
Sonnet 5 $0.00000 $0.00126
Haiku 4.5 $0.00000 $0.00063

Measured 2d ago against content hash 69f45fcf750a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

fortran 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.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

  • fortran — 98% identical, 1 lines differ
rules/fortran.mdc · 67 lines

How it starts

The opening of the file, as written. The whole thing — 67 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Fortran Programming Guidelines

Basic Principles

  • Use modern Fortran standards such as Fortran 2003, 2008, or newer.
  • Use implicit none in every program unit.
  • Put procedures in modules to provide explicit interfaces.
  • Keep modules focused and place each major module in its own file.
  • Prefer clear, structured code over clever language tricks.
  • Avoid obsolete features such as COMMON blocks, GOTO-heavy control flow, and numeric labels.

Kinds and Types

  • Define numeric kind parameters in one shared module, such as kind_mod.
  • Use real(kind=dp) or the project-approved real kind for floating point values.
  • Use integer(kind=i4) or the project-approved integer kind for integer values.
  • Define constants such as pi explicitly.
  • Include units in comments for physical quantities.
  • Use derived types to group related data instead of passing many primitive arguments.

Naming and Style

  • Use lowercase for language keywords and most identifiers.
  • Use underscores for multi-word names.
  • Avoid names that differ only by case.
  • Use descriptive names for procedures and state.
  • Repeat the procedure or module name after end statements.
  • Keep indentation consistent in do, if, select case, and module blocks.

Procedures

  • Keep subroutines and functions short and single-purpose.
  • Use intent(in), intent(out), or intent(inout) for every dummy argument.
  • Keep functions free of side effects whenever possible.
  • Prefer early validation and clear returns over deep nesting.
  • Use use, only: when importing from modules.

Memory and Arrays

  • Prefer allocatable arrays over pointers unless pointer semantics are required.
  • Check allocation state and array sizes before use.
  • Deallocate allocatable arrays when their lifetime is not naturally scoped.
  • Specify array bounds clearly when they matter.
  • Avoid unnecessary dynamic allocation in hot loops.

Testing and Build

  • Use CMake, fpm, Make, or the project-standard build system consistently.
  • Compile with warnings enabled and treat important warnings as failures in CI.
  • Add unit tests for public procedures and integration tests for numerical workflows.
  • Test boundary conditions, invalid inputs, and representative scientific cases.
  • Verify numerical tolerances explicitly rather than relying on exact floating point equality.

Read the full file on GitHub · 67 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 · 67 lines · 0 tokens per session scan A 69f45fcf750a

Subscribe to this mod's changes

fortran is a cursor rule published in the GitHub repository PatrickJS/awesome-cursorrules (40,694 stars, last pushed 3mo ago), licensed CC0-1.0. It costs nothing until one of its globs matches a file; then it loads 631 tokens. 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.