Technical

4 Minutes

TLDR: Download the best disk cleanup app in existence from diskspace.io. A fun experiment in writing the same app three times (well kind of 4 times) with AI, and being as optimised and OS native as possible.

My Mac recently filled its 1TB drive and my quest to find out where the space had gone was very frustrating. The existing tools for tracking down disk space were slow, clunky and it was impossible to use them until their 30 minute crawl of my hard drive completed.

I decided to fix this by building a new app called Disk Space, which takes the great features of my favourite old time app Disk Inventory X, makes it blazingly fast and adds much improved file/folder deletion aesthetics so that you can clean up safely and quickly, as well as highlighting recently created files so you can find what changed more quickly.

Let’s get nerdy

The three versions, Mac, Windows and Linux, are all mostly independent, with just a little shared C++ code. My goal was to make each app as small, fast, as native to its environment as possible. This meant not using any of the more common cross platform libraries, and leaning on Claude to do the work.

MacOS

The MacOS version of Disk Space is written fully in Swift, with no dependencies on other libraries. This was the first version I built. It detects how many CPU cores your machine has and optimises itself to maximise the throughput. The size of the installed app is just under 1MB, with about 300KB of that being multiple sizes of the icon, so the app itself is just over 600KB in size. Not bad!

Releasing desktop apps for the Mac is actually not too bad an experience. You can choose to put it in the App Store, but then it can be a pain to release a new version. Apple offer a free notarisation service that signs the built app with your Apple Developer credentials, and it works well. For this reason, you can simply download the MacOS version of Disk Space from the site.

Windows

The Windows version is a direct port of the Swift code to C++. Similar to the MacOS version it optimises its operation based on the number of cores, but it also checks if the drive being scanned is a spinning disk or a solid state drive. If it’s a spinning disk there’s no point running many threads against it, it’s physically incapable of responding, so it caps the number of threads. Since it it just pure C++ with no dependencies pulled in, the installer is just about 600KB, pretty cool.

Releasing apps on Windows these days generally means you are forced to either release through the Microsoft Store or pay for quite expensive yearly fees to have your app notarized. Without this, the user will be shown very scary warning dialogs, making the app very hostile to use. Since this is a small free app, I went the Microsoft Store route.

Linux

The Linux version shares some of the C++ with the Windows version, especially the code that draws the multi-coloured tree map on the right. Similar to the Windows version, it checks the hardware of your storage to best optimize itself and otherwise builds the UI using Linux native code with almost not dependencies. The first version Claude recommended depended on the GTK libraries for the UI, which was convenient, but it meant that using the app on any system that didn’t include those libraries would force the user to download hundreds of megabytes just to get a 500KB app running. Luckily, within an hour Claude had completely rewritten the app to be almost fully self contained.

This means that the Linux app, which is packaged as an AppImage file, is just about 600KB all in, and you can simply download it from the site.

Epilogue

This was a fun experiment in building an identical app for all three operating systems while keeping it as native and optimised as possible. The hardest part was the hardware setup required for testing.

I now have on my desk:

  • My MacBook Pro (my primary machine). I do most of my work on this, run Claude and do all testing of the MacOS app.
  • A small but powerful Windows Desktop. This is pretty great, as not only can Claude build and test Windows apps on it, it can also build and test (to some degree) Linux apps too. I use this as the main machine for those two operating systems.
  • An ancient, 2009 MacBook Pro 17″ that I installed Linux on just for building this app. I use this for testing the Linux version on a real machine, not just on Windows WSL. It works relatively well, but with just 4GB of memory I won’t be doing any development on it any time soon. Still, it’s great to make use of the old hardware instead of throwing it away – I knew there was a reason I hung on to it!
  • … a lot of messy crap I need to tidy up. Any day now….

I can’t believe you read this far, thanks! Now go get Disk Space from diskspace.io, your hard drive will thank you 🙂

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Published by Shane O'Sullivan

I am a software engineer and manager from Ireland. I spent 7 years working in Ireland from 2003 – 2010, then ten years in Silicon Valley from 2010 to 2020. In California I spent about 6.5 years at Facebook Engineering, the last three of which I was an engineering manager in the Ads organisation focusing on customer facing products for creating and managing ads. At Stripe I built the Developer Productivity organisation, with teams that were responsible for the use of the Ruby language, testing infrastructure, documentation, developer tooling (e.g. IDE integrations) and more. At Promise, I was Head of Engineering from 2018 – 2020, responsible for building the first few iterations of our products, hiring for all product roles, meeting with clients and investors, and anything else needed to get a tiny startup bootstrapped and successful. Now I’m back in Ireland, working various projects while advising the great people at Stainless (stainless.com). This blog contains my various musings on all things technical/interesting on the interweb and beyond.

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