Dragging Fortran kicking and screaming into the 21st Century

Author: Ben Bradley, Feb 2026 (last updated: Feb 2026)

What is Fortran?

Fotran is one of the first programming languages, wiht the first versions dating back to the 50's. It is a compiled language, which means code is compiled to faster machine code before it can be run (unlike Python which is compiled just-in-time). It has been used extensively in scientific modelling for many decades, and will likely continue to be used for some time still.

Why use fortran?

Speed: Fortran is much faster than Python and other high-level languages
Legacy: many established scientific models use Fortran, making it essential for adding to or modifying the existing codebase
Self-hatred: you're some sort of masochist who enjoys declaring the types of all variables

How to minimise the pain

If you find yourself in the unenviable situation of needing to code in fortran, do not dispair! You don't have to code in the terminal like some sort of caveman! VS Code has an extension called Modern Fortran to solve all of your problems. This can provide wonderful features such as:

Syntax highlighting
Linting (before compiling!)
Rulers
Variable auto-completion
In-line AI code suggestions
Easy and intuitive committing of code to GitHub
All the other lovely features included within VS Code.

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Setting Up

I assume here that the reader is already familiar with VS Code and Python Environments (e.g. Miniforge). If you're not, consult BAG's Guide to VS Code and Guide to using Mamba via Miniforge

1) Starting

Open VS Code, ssh into the machine you wish to code on, and open the folder of your project. Install the Modern Fortran extension from the extensions tab.

2) Create a Fortran environment

Activate conda if you haven't already:

conda activate

Create a new environment:

mamba create -n fortran

Activate your new environment:

conda activate fortran

Install the fortls and gfortran packages:

mamba install fortls gfortran

3) Tell VS Code where the packages are

Open the settings.json file by hitting Ctrl+Shift+P and typing json into the search bar that opens up. Click on "Preferences: Open Remote Settings (JSON) (SSH: [machine])" if you're connected to a remote machine. Add the following to the file (which is likely empty):

{
    "fortran.fortls.path": "[mypath]/miniforge3/envs/fortran/bin/fortls",
    "fortran.linter.compiler": "gfortran",
    "fortran.linter.compilerPath": "[mypath]/miniforge3/envs/fortran/bin/gfortran",
    "fortran.formatting.formatter": "fprettify",
    "fortran.linter.includePaths": "[mypath]/miniforge3/envs/fortran/include",
}

Replace mypath with the path to your Miniforge directory.

4) Add a ruler

Old versions of Fortran have a strict character limit for lines of code, and can fail to compile code after this limit. To avoid these errors and to help keep code to best practices, I like to add a ruler to the screen at the character limit.

{
    "editor.overtypeCursorStyle": "line",
    "terminal.integrated.defaultProfile.windows": "Git Bash",
    "[FortranFreeForm]": {
        "editor.rulers": [132]
    },
    "workbench.colorCustomizations": {
        "editorRuler.foreground": "#458cff"
    },
}