Style guide

Fantomas tries to adhere to two F# style guides: - Microsoft - G-Research

By default Fantomas will format the code according to the Microsoft guide.
The benefit of these guides is that this allows us, as the F# community, to write code in the same manner.

Let it go

If you are not used to having a code formatter, you might struggle a bit at first. A part of using a code formatter is about letting go how you wrote things and accept a common consistent style instead.
When embraced, this can truly be a liberation feeling. You can play jazz while typing the code, focus on the task at hand and have the same output as if anyone in your team would have written it.

A cautionary tale

The responsibility of the coding style is also a shared one. The maintainers of Fantomas do not dictate how things should look like.
Instead, conversations are held over at fsharp/fslang-design.

Over the years, a lot of consumers of Fantomas have requested numerous features. These often go against the philosophy of being consistent amongst the community. If there were a gazillion of settings to please everybody it would be a missed opportunity to see all F# code bases in the same style.

And more importantly the maintenance cost of each setting is always carried by only a handful of people. The hardship of having a setting is so high that in almost all cases it is not worth having it.
Even when someone proposes to contribute the setting, it always leads to lament and sorrow for the maintainers to carry.

Default style guide

As mentioned, the default style guide is not to be discussed on the Fantomas repository. The majority of the maintainers is burnt out talking about style at this point.
If you want to discuss the style, you are more than welcome on fsharp/fslang-design.

However, we greatly encourage that you take some time to understand the Fantomas code base. Having an opinion on code style is easy, everybody writes code so we all have our thoughts and feelings about it. Being able to translate your thoughts/opinions and prototyping them in Fantomas will gain you a much larger insight on how quickly things can get quite complex.

At the end of the day, if some new idea is validated on fsharp/fslang-design, it needs to be:

There’s no such thing as a free lunch, so please consider all aspects of debating code style.

G-Research Style

G-Research has been our single enterprise sponsor for the last five years. Fantomas would not exist in it's current form if it were not for their support.
Their interest was to have a tool that automatically format code according to their internal guidelines. These have been made available publicly and can be turned on via various settings.


To strengthen the message of unity we advice that you do not change the default settings. The out-of-the-box experience should be a result of what the brightest minds of the community came up with. If you are new to the F# language, this is what you want.