Akkurat Typeface (lineto.com)

I'm excited to share a small web app I built that allows you to view and extract the contents of Windows MSI installers directly in your browser. It's essentially a web-based "lessmsi" powered by Pyodide.

You can try it out at: https://pymsi.readthedocs.io/en/latest/msi_viewer.html

My motivation for building this was from part of my day job -- I often get Windows MSI installers and need to extract files while preserving the relative directory structure and filenames, as they would appear after a full installation. The existing tools I found were good but limited in which platforms they support: lessmsi works great on Windows, while msitools works for Linux/macOS. Neither is a truly cross-platform solution that works on any major OS.

So we developed pymsi (a pure Python library, available on GitHub at https://github.com/nightlark/pymsi) to handle reading and extracting MSI files from Python. Then I realized that since pymsi has no native dependencies, it could potentially run in a web browser using Pyodide. After a bit of "vibe coding" and fixing some "hallucinated" functions/classes that don't exist in pymsi, the result was this client-side web app.

If you need an MSI file to experiment with, older versions of PowerToys included the installer in .msi form, such as this one: https://github.com/microsoft/PowerToys/releases/download/v0....

Note that the underlying pymsi library hasn't been extensively tested against a bunch of MSI installers yet, so there might still be lingering bugs. If you come across any issues, please don't hesitate to report them in on the GitHub repository (https://github.com/nightlark/pymsi/issues).

I'd love to hear your feedback and answer any questions!

Comments (8)

danielodievich · 7m ago

I was there at Microsoft in the beginning of MSI, which was what, Office XP? Gosh or was it 2003? The tooling for dealing with them was super jank then. I could have never predicted that you'd be able to just casually open it in a browser. Nice job man!

pragma_x · 2h ago

I feel like this would also solve the "I just need the printer driver file(s), not everything else" use-case. Nice work.

blangk · 1h ago

Printer drivers rarely if ever come in MSI format. They most commonly use self extracting exe archive.

Lanrei · 33m ago

Neat. I usually just use 7zip to open .exe and .msi files.

hypercube33 · 17m ago

I don't think 7zip really can see into a lot of janky MSI files to get the actual installed content, can it?...it can technically break open NSIS files and get the source but that is disabled in code after 15.05 (GitHub has a mod to renable source extraction fyi) and yes self extracting exe files.

rmast · 2h ago

As a side note, I just tried it in mobile Safari on my iPhone -- at least inspecting MSI files works, extracting files may work as well (not sure where it is placing the "downloaded" zip file).

jasonjmcghee · 1h ago

My safari puts things in icloud drive / downloads

lxgr · 28m ago

That's configurable in the Safari settings, fwiw (I personally prefer my downloads to not automatically become uploads, especially on mobile data).