All about F# Files

The F# file type is primarily associated with F#.

F#	File extension: F#
	File type:	Source Code

What is an F# file

F# files mostly belong to F# by Microsoft Corporation. F# (pronounced F Sharp) is a scalable, succinct, type-safe, type-inferred, efficiently executing functional/imperative/object-oriented programming language. It aims to be the premier type-safe functional programming language for the .NET framework and other implementations of the Ecma 335 Common Language Infrastructure specification. F# was partially inspired by the OCaml language and shares some common core constructs with it. The inputs to the F# compiler or the F# Interactive dynamic compiler consist of source code files, with extensions .fs, .fsi, .ml, .mli, .fsx, .fsscript.

Files with extension .fs, .ml must conform to grammar element implementation-file.
Files with extension .fsi, .mli must conform to grammar element signature-file.
Files with extension .fsx and .fsscript are processed just as for those with extension .fs except that the conditional compilation symbol INTERACTIVE is defined instead of COMPILED, the assembly FSharp.Compiler.Interactive.Settings.dll is referenced by default, and the namespace Microsoft.FSharp.Compiler.Interactive.Settings is opened by default.

How do you open F# files?

You need a suitable software like F# to open an F# file. You need a suitable software like F# from Microsoft Corporation to open an F# file. Without proper software you will receive a Windows message "How do you want to open this file?" or "Windows cannot open this file" or a similar Mac/iPhone/Android alert. If you cannot open your F# file correctly, try to right-click or long-press the file. Then click "Open with" and choose an application. You can also display a F# file directly in the browser:. Just drag the file onto this browser window and drop it.

Online F# Text Viewer

Choose your .f# file to analyze

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Online File Viewer

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What to Do When a .F# File Fails to Open

Because .F# files can originate from different environments, they aren't universally openable.

Identify the Source: These often come from software developers or data analysis workflows, suggesting they are Microsoft F# source code files.
Check the Header: Open the file in a text editor to inspect its opening lines. You might see:
- Readable code like open System, confirming it's an F# script.
- "PK" magic bytes, indicating a ZIP archive rather than standard source code.
Use the Original Software: The original program is usually required; try Microsoft Visual Studio or Visual Studio Code. If uncertain, ask the sender.
Use this Webpage: Drag and drop your file into our viewer to detect the format, extract readable text/metadata, and preview when possible.

Technical Data for F# File Extension

File classification:

Source Code

Related files:

mli, fsx, fsi

an f# Source Code is a special file format by Microsoft Corporation and should only be edited and saved with the appropriate software.

How to solve problems with F# files

Associate the F# file extension with the correct application.
Update your software that should actually open source codes. Because only the current version supports the latest F# file format. Search, therefore, e.g. on the Microsoft Corporation manufacturer website after an available F# update.
To make sure that your F# file is not corrupted or virus-infected, get the file again and scan it with Google's virustotal.com.
Click here to open your .F# file online - secure, fast, and no downloads needed.