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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
One of the absolutely coolest features of Kidz Fun Art is the ability to create Animations. This was initially inspired by watching my nieces creating an animation on another Android app, so I focused purely on the creation case. This worked well, where most animations were under 50 frames in length, as it takes time to create them. I later added the ability to import Gif images, since it was a relatively simple change – parse the Gif image into frames, save them and boom, you can edit and re-export it. However this exposed a problem: Gifs can be huge, and Kidz Fun Art didn’t work well with thousands of animation frames of data. I wasn’t sure where the bottlenecks were, but at some point the app would just crash if the Gif was big enough, of if the user created an animation over 100 frames or so. This is all now fixed, and the app comfortably imports multi-Megabyte Gif images and provides a better user experience when some operations (like deleting hundreds of frames) are not instant. Using AI to find performance issues & subtle bugs While I have always written the vast majority of the code for Kidz Fun Art by hand (using AI for more complex things like WebGL shaders and C++ based paint brush simulation), it’s been invaluable recently for reviewing and testing the code. I asked Claude Opus 4.8 (the current frontier model as of July 2026) to identify the bottlenecks and it did a great job. There were multiple places where I initially wrote a function to take an action on a single frame that would then save the full animation, but later reused this function in a loop over all the frames. This caused the full animation to be saved hundreds of times in a few seconds, crashing the app. The list of frame thumbnails at the bottom of the screen rendered all thumbnails up front. This is fine for 50 but not for 1000. When saving a Gif, the file was far too large. This is because it wrote each frame in its entirety to the Gif image. The Gif standard obviously supports just writing the pixels that changed from the previous frame, and I wasn’t doing that. Deleting a large animation would take multiple seconds, with not user feedback. This was fine for other media types as they are more or less instant, but in this case it let the user click around the app, then have unexpected things happen 5 seconds later. It made the app feel broken. Gifs that stored some frames with the option to simply restore the previous frame were not handled, making the import of some images be inaccurate. There were a number of places where race conditions between multiple asynchronous actions could cause bugs. The AI was very good at finding places where my code should have been waiting for one to complete before beginning the second. There were multiple places where memory leaks occurred, specifically with not cleaning up event listeners. It found them all. When leaving the app open for days or weeks at a time without a reload, this could have been a real problem. What is better now? Animations now scale up to very large sizes, with instant access to all frames. You should be able to import basically any reasonable Gif image, and it will be exported in a highly optimized manner, with perfect colour matching per pixel. When deleting a large animation, you are told it is being deleted immediately, so it’s obvious the app is doing what you asked it to do. When importing a large Gif, you are shown a dialog telling you that it is happening, and blocking you doing other work until that completes. Many subtle bugs fixed. The frame list is fully virtualized, and scales up to essentially any size of animation. We have tests now! Another great use of AI is for writing tests, in this case laboriously creating dozens of large integration tests. These were invaluable in both validating the deep changes being made and in finding more edge cases and race conditions. Kidz Fun Art now has full end-to-end tests covering animations, layers, comics, cards, drawing, colouring, handwriting, maths and puzzles. I hate writing these, but AI doesn’t get bored, and I look forward to adding more and more regression tests in the future to keep quality high for all the world’s young artists out there.
For a long time I’ve wanted to add Spirographs to my (awesome ) drawing app for kids, Kidz Fun Art, and today it’s ready! There was quite a bit of fun mathematics in getting it to feel natural and work with all sizes of circles, but it seems to have worked out very well! You can move the Spirograph around, change the size of the outer and inner circles, and draw in any colours you like. Read more about it on the main blog post here, try it out on the web at https://kidzfun.art , get it for iPad here, or download for Microsoft Windows here.
Way, waaayyy back in 2010, I built a fun little game for the Palm WebOS series of phones called Mazer. I was happy with it, loads of people downloaded and played it, and then WebOS died. I recently found the source code again, and with the help of Claude AI I rewrote it to run on iOS and iPad! Get it for free today from the iOS App Store. (Android version coming soon) There are four different game types You can find your way around a simple maze, or race a terrifying fiery ball to the finish. Over 120 hand crafted obstacle courses to get around with worm holes, force fields, evil fiery balls, and more. My personal favourite, a Pacman like maze where the four ghosts chase your little ball around as you try to open the portal and get outta there!
I’ve been using the Irish energy provider Energia for 5 years or so (as of writing, 2026) and they used to have a useful insights dashboard that let me analyse my power usage. Well, they seem to have removed it so I built a handy dashboard that anyone can use. It’s at https://energy.chofter.com/ , try it out! You simply download your power usage information as a CSV file (a spreadsheet) from their site, currently at https://energyonline.energia.ie/my-account/half-hourly-usage/ . Then drop the file into the web app and it will: Show a useful overview of your usage for the full time period You can configure your current home setup This includes specifying your current tariff, whether or not you have a home battery or a car Compare usage versus last year Shows a heatmap of your usage by every 30 minutes Simulate the change in cost if you change your home setup Try out what would happen if you kept your consumption the same but changed your tariff, or added a battery or a car. This one is particularly useful.
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Reading my recent computing retrospective, I realised there was a big section missing: the people in my life that made an impact and helped shape my career. Outside my immediate family, one person made an outsized contribution, and I’m fairly certain that without his influence my life would have taken a very different path. The fact that I’m still here in 2026, still writing code and being fortunate enough to have a career in something I love is testament to him. So I’d like to take a few moments to talk about my old secondary school teacher, George Dryden. Denied Back in 1995, I had a problem. I knew I wanted to study computing at university and build a career out of my passion, but there was a snag. For those unfamiliar with the UK schooling system, when you’re 15-16 you take a set of GCSE exams in a broad range of subjects. After that, you pick around 3 subjects to really focus on over a period of 2 years. These are called A Levels, and they are a big step up and are meant to prepare you for a degree-level course at university. Admission to university is also governed by these results - if you want to study computing, you’re going to need a computing A-Level, and most universities will only accept you (or “make an offer”) if you achieve a certain grade. And whilst I had taken computing at a GCSE level, my school did not offer a computing A-Level course. I instead had to settle on “Design & Technology”, which just didn’t inspire me. Instead of working on my portfolio and projects, I spent most of my time daydreaming and writing code on the Acorn Archimedes computers that were the staple of every 90s UK school. No disrespect to the teachers - they were all awesome - but it just wasn’t for me. I was miserable, and by the end of my first year, I was well on my way to failing outright with my entire future plans seemingly going up in smoke. Someone noticed That’s when George stepped in. He’d taught me computing right the way through my GCSEs, and with no A-Level course on offer, that was officially where his involvement was supposed to have ended. It didn’t. He had noticed my constant presence in the computing labs - before and after school, during lunch breaks, free “study” periods - working on some little pet project or digging into RISC OS internals. I remember him as warm, with a wicked, dry sense of humour, and a refreshingly spiky attitude to authority - I always got the sense he’d worked out for himself which rules were worth taking seriously and which ones weren’t. And he always had time for me. I spent years pestering him with questions that had nothing to do with anything on the syllabus, and he’d always find a way to answer them that actually made sense. He was just as supportive of my odd little obsessions. At one point I’d got deep into the BBS scene, which I thought was the coolest thing ever, and decided what the school really needed was an internal BBS running on its own network. So I wrote one. It was deeply cringeworthy, obviously - but George helped me put posters up around the school advertising it, and even gave it a mention in assembly one morning. I think about five people in total ever checked it out. It didn’t matter: a teacher had stood up in front of the entire school and treated my weird little project like it was worth something, and that was a hugely validating moment for me. Off the books He recognised the passion, and eventually he made a suggestion: What if I quit the Design and Technology course, and instead attempt the A-level course myself? Personally, I also suspect he was enjoying himself. There was some internal school politics behind why computing wasn’t offered at A-Level in the first place - I never knew the details - and I think the prospect of one of his students simply going out and getting the qualification anyway appealed to him on two separate levels. It would get me where I wanted to go, and it would wind up exactly the right people. It wouldn’t be easy, he warned. The school would be against it, plus it was a two-year course which I’d have to cram into one year. I’d have to do it all myself - studying, lesson planning, coursework - he couldn’t help me in an official capacity, but he said he’d advocate for me and help where he could. If I had assignments, he’d send them off to be graded and would give feedback in his own time. He’d enter me in for the exams and also gave me a set of keys to the computer lab so I could use it whenever I needed. It was the first time anybody outside my own family had really shown faith in my abilities and encouraged me to take a stand. It was a pivotal moment for me - I realised if I wanted something badly enough I would have to fight for it, but I could still make it happen. I didn’t have to take “NO” for an answer - a lesson I think I picked up from watching him as much as from anything he ever actually said to me. After a few weeks of dithering, I took the jump. I remember a few awkward meetings with the school administration but thanks to his behind-the-scenes work, I was soon following my dream. An intense year And yes, it was bloody hard work. I had to condense an entire two year course into under a year, be disciplined enough to produce my own study plan, and be critical enough of my own shortcomings that I could focus my study where it was needed. I pretty much lived and breathed it for months straight and was more-or-less a permanent fixture in the labs or school library poring over my course books. I’d make lists of questions and chat to George over lunch, and he’d provide guidance and encouragement. It was a lonely way to learn with no classmates to compare notes with, no lessons to turn up to, and right up until the end I had no real idea whether any of it was good enough - but bit by bit, it started to feel like something I could actually pull off. And sure enough, in the late spring of 1996, I sat down in an exam hall with my fellow students, the only one with an A-Level computing question paper in front of me. The final exam went by in a blur - I can only remember a few of the questions now (and a peculiar obsession with the Pascal language) - but I do remember the euphoria as the invigilator called “time’s up, pens down, close your papers NOW”. I had done it. A few nerve-wracking months later, my Mum drove me into school to pick up my results. I ripped open the envelope and saw it - I’d passed with an A grade! I literally ran up the stairs to George’s office next to the computing labs to thank him personally. I’d taken my camera into school to take a few last photos for memory’s sake and snapped this photo of him before I walked out the school gates for the last time: A different path Because of him, I managed to get into my university of choice, studying computing with a focus on networks. Because of that, I landed my first job working as a “webmaster”, and my career since has been one of the highlights of my life. All these years later, it’s a real privilege to be able to get up each morning and actively look forward to working in an industry I love. Without George stepping up for me and encouraging me to believe in myself, none of that would have happened. I wouldn’t have had the career I have, and I wouldn’t be where I am now. I met my wife when we both worked at a software company - she sat at the desk behind me - so even my home and family life can be traced back to that spring of 1996. And the A-Level itself was only half of what I took away from that year. The qualification opened the door to university, but the lesson that came with it was every bit as important: that a “no” isn’t always the end of it, and that sometimes the answer can be argued with. I’m so proud of what I managed to achieve all those years ago, and even more thankful to have had someone like George in my life to put me on the right track. Mr. Dryden I did see him again after I left. He drank in one of my local pubs - a pub I’d been going to for a good while before I was technically old enough to be in it - and I’d say hello if I spotted him in there, mostly in the months before I moved away to university. After that it was only a handful of times. For years I’d find myself scanning the room whenever I was back home and in for a pint, half expecting him to be at the bar. At some point I stopped seeing him altogether and eventually moved across the country. The trouble was I never really knew how to talk to him outside of school. He was always Mr. Dryden, or just “Sir”, I don’t think I ever once called him George to his face! I was (and still am if I’m honest) fairly socially awkward, and I never worked out how to phrase the thing I actually wanted to say: that he had changed the entire direction of my life, and I wasn’t sure he knew it. So instead I’d say hello, and ask how he was, talk about nothing much, and go back to my friends. Epilogue Sadly, 3 years ago now, I opened the latest issue of my old school alumni newsletter to read that he’d passed away. The photo at the start of this article was taken from his obituary article and I read that he’d had a long illness and had suffered from dementia at the end. I did write to him years ago by email - I don’t know if he ever got it, or was in any capacity to understand what he’d done for me, but I hope so. There’s an old saying by one of my favourite authors (Terry Pratchett) that “no one is finally dead until the ripples they cause in the world die away”. In one of his books, a character keeps the memory of his son alive by passing his name along a series of telegraph towers. It’s in that spirit that I’m writing this post - I debated it for many years as it’s very personal to me and I also have no contact with any of George’s family so I have no idea what they would make of it all. But even though it’s 30+ years ago now, I will never forget him or what he did for me - and at least now, if someone searches his name it’ll be recorded here for as long as I’m alive and running this site. Thank you, Sir. George Dryden 1942-2023
Let’s step inside the kernel and understand how it implements copy-on-write and what are its implications for the performance of user-space systems
Yesterday, I received this email as a response to You Can't Vibe Code Love. It's such a remarkable and powerful statement that I asked permission to share it here, in its entirety, with personal information redacted: Hey Jeff, Hope you and your family are doing well.
A frustrated Reddit post about being a condom between an AI and production made the rounds in our team. Here is why I think the opposite is true and what it means for how we review code, plan work and think.
And here we are three years after I wrote about the Google Pixel Fold being announced, followed now with the announcement of the iPhone Duo...(I have questions about the naming by the way). Four years ago I was talking about web primitives in the platform for the Surface Duo. My how time flies. There are CSS media features, a Viewport Segments API, a Device Posture API but Chromium based browsers are the only ones currently supporting these things. I haven't been able to find any signal yet on whether Safari will support these things in the web platform as the developer docs focus on application development. If you're interested in trying out the platform features, you can emulate the Surface Duo and Galaxy Z Fold in the developer tools. And if you're thinking, do I really have to have my website adapt to two screens? The answer is no. Adding a design to an application or dual screen makes sense if you have an experience that has two simulataneous contexts that are useful e.g. a list of email messages/inbox on one screen, an open message, email thread or email composer on the other. Here's one of my talks from 2022 if you're interested in learning more about what's available in the browser for dual screen/foldable devices. Happy building :)
