The flat assembler (abbreviated to fasm, intentionally stylized with lowercase letters) is a fast assembler running in a variety of operating systems, in continued development since 1999. It was designed primarily for the assembly of x86 instructions and it supports x86 and x86-64 instructions sets with extensions like MMX, 3DNow!, SSE up to SSE4, AVX, AVX2, XOP, and AVX-512. It can produce output in plain binary, MZ, PE, COFF or ELF format. It includes a powerful but simple macroinstruction system and does multiple passes to optimize the size of instruction codes. The flat assembler is self-hosting and complete source code is included.
The only difference between flat assembler versions included in the following packages is the operating system on which they can be run. For any given source text each version is going to generate exactly the same output file, therefore every one of the following releases can be used to compile programs for any operating system.
Publisher’s description
What is Flat Assembler?
Flat Assembler by fasm is open-source Windows software. It is written in Assembly.
Installation and requirements
The publisher provides Portable installers for 64-bit and 32-bit Windows. It runs without installation (portable).
Updates and version history
The current version is 1.73.32, released on May 22, 2025. The version history goes back to February 21, 2022: 2 releases, all linked to the official files. That is about 0.6 releases a year. The last update is more than a year old.
Popularity and file types
The source code on GitHub (tgrysztar/fasm) has 1,790 stars.
Project description on GitHub: “flat assembler 1 - reconstructed source history”
Pros / Cons
Pros
- Open source: the code can be inspected and built by anyone
- Portable: runs without installation
Cons
- No native ARM64 build
- No update for more than a year
- The official download link did not answer at the last check
In short: Flat Assembler is an open-source Windows tool for 64-bit and 32-bit PCs. Updates have slowed down.
Is Flat Assembler safe to download?
- The file is served by flatassembler.net, the publisher’s own domain
- The download link uses HTTPS
- A SHA256 hash is published, so you can verify the file:
D8FE204AAB01046FFAB3651EF9FF6F1AB72EA907CC2AB2B34FEFD774E5814948· Open the VirusTotal report for this hash - The link did not answer when we last checked it (October 22, 2026)
- The source code is public
- ExeAtlas does not host, wrap or modify installers
Related guide: How to check a file’s SHA256 hash on Windows
Recent versions
All 2 versions ›2 versions over 3 years · about 0.6 a year
| Version | Date | Size | Files |
|---|---|---|---|
| 1.73.32Latest | May 22, 2025 | — | 32-bit ZIP64-bit ZIP |
| 1.73.30 | February 21, 2022 | — | 32-bit ZIP64-bit ZIP |
Install from the command line
Silent install ›winget install --id fasm.fasm -escoop install extras/flat-assemblerRelated guide: How to use winget: install and update apps
Information
- Publisher
- fasm
- Licence
- Simplified BSD
- Price
- Free
- Source code
- github.com/tgrysztar/fasm
- Written in
- Assembly
- Requires
- Windows 11 / 10
- Architecture
- 64-bit, 32-bit
- Installer
- Portable
- Version
- 1.73.32
- Released
- May 22, 2025
- Added to the catalogue
- April 28, 2023
- Versions listed
- 2
- Updates / year
- 0.6
- GitHub stars
- 1,790
- GitHub forks
- 69
- Website
- flatassembler.net
- winget ID
- fasm.fasm
- Scoop package
- extras/flat-assembler
Ratings and reviews
No reviews yet. Be the first to rate it.
Frequently asked questions
Is Flat Assembler free?
Yes. Flat Assembler is open-source software under the Simplified BSD licence.
Is Flat Assembler safe to download?
The download comes from flatassembler.net, which belongs to the publisher; ExeAtlas does not host or change the file. Compare its SHA256 hash with the one shown here, or open the VirusTotal report for that hash.
How do I install Flat Assembler with winget?
Open PowerShell or Windows Terminal and run the winget command shown on this page. winget downloads the official installer and checks its SHA256 hash before running it.
Does Flat Assembler run on ARM (Windows on Arm)?
There is no ARM64 build; Windows 11 on Arm can run the 64-bit and 32-bit version through emulation.
Where can I download an older version of Flat Assembler?
The versions page lists all 2 versions with links to their official installer files, back to February 21, 2022.
Can I use Flat Assembler without administrator rights?
Yes, it is portable: unpack and run it.