FSI File Extension
Visual F# Signature Format
- File Type fsi
- Developer Microsoft
- Popularity
- Application Windows Notepad
- Category Developer Files
- Format Text
What is a FSI file?
The FSI extension is related to Visual F# Signature Format and is classified in the Developer Files category, which contains 1166 files.
The Visual F# Signature Format (FSI) was created by Microsoft, a company that developed file format and produced 242 programs for their use.
FSI files are compatible with various operating systems, including Mac OS, Windows and Linux. If you need to open a FSI file, you can use one of 8 programs, such as Microsoft Visual Studio, Atom and Windows Notepad.
Programs that support FSI files
How to open a FSI file?
If you’re having difficulty opening a FSI file, it is often due to not having the correct software. To solve the problem, choose a compatible program from the list. Then follow the link to the official developer site, download the software, and install it on your device.
Microsoft Visual Studio, Atom and Windows Notepad are among the most widely used programs for handling FSI files. To set up the newest version of Windows Notepad on your device, simply go to the official Microsoft website. There you can download the edition compatible with every operating system.
Once the process is complete, Windows Notepad should take over as the default application for FSI files.
Make Windows Notepad the default FSI viewer
Change the default app to open files on Mac
- Right click or use Control + Left Click on the desired FSI file to access a dropdown menu of actions;
- Choose "Open in Application" and click "Other";
- At the bottom of the window, you will find the "Enable" menu. Default, will be set to "Recommended Programs";
- Choose "All Programs" in this menu and search for Windows Notepad. Check the box next to "Always open in app" to make it the default program.
Change default programs in Windows
- Start by right-clicking on your FSI file, then select "Open With" and continue by clicking "Choose another app" from the options provided;
- Inside the popup window, scroll through the list of applications and specifically choose Windows Notepad as the application to associate with your FSI file;
- Check the "Always use this app" checkbox and click "OK".
Finding answers to FSI file problems
Rest assured, any issues with FSI files can typically be addressed with simple software adjustments. See the tips below for help.
What are the steps to repair a damaged FSI file?
Open the damaged FSI file in a recovery program and select the "Repair" menu item to start the repair operation. Allow the recovery process to complete, which will automatically repair the damaged developer files.
What are the methods to detect if my FSI file has been corrupted?
The signs of corrupted FSI developer files can manifest as:
- Unexplained FSI file size inflation;
- Windows Notepad or other programs stop responding or crash when trying to handle the file;
- When opening the file, errors occur or the inability to access its contents;
- While working with the file, error alerts are encountered;
- The file shows slow performance when edited in Microsoft Visual Studio;
What are the reasons behind Windows Notepad crash?
Insufficient software updates can contribute to Windows Notepad crash. To avoid this, make sure that you have installed the latest updates for Microsoft products.
A computer restart is often the key to solving numerous common problems. That’s why, it is recommended to restart the computer before making any changes to the software settings.
How to edit a FSI file?
To modify FSI files, it is necessary to install dedicated software that lets you open and edit developer files. Online FSI editors generally offer fewer tools compared to programs designed for Visual F# Signature Format.
Best FSI Editor Software in 2026
Based on the criteria above, here is a selection of FSI editors you can use.
| FSI Editor Software | Developer | Platforms | Overall Rating |
|---|---|---|---|
| TextEdit | Apple | Mac OS | 4.8 out of 5 (40 reviews) |
| GNU Emacs | FSF | Linux | 4.7 out of 5 (33 reviews) |
| Gedit | GNOME | Linux | 4.6 out of 5 (38 reviews) |
| Notepad++ | Notepad++ Team | Windows | 4.6 out of 5 (37 reviews) |
| Sublime Text | Sublime HQ Pty | Windows, Mac OS, Linux | 4.6 out of 5 (39 reviews) |
| Microsoft Visual Studio | Microsoft | Windows, Mac OS, Linux | 4.2 out of 5 (35 reviews) |
| Windows Notepad | Microsoft | Windows | 4.2 out of 5 (37 reviews) |
| Atom | - | Windows, Mac OS, Linux | 4.1 out of 5 (36 reviews) |