Michiels Blog

65 lines of Markdown - a Claude Code sensation

2026-02-12T08:00:00+01:00

Yesterday my employer organized an AI workshop. My company works a lot with AI supported code editing; using Cursor and VS Code, GitHub Copilot. Plus we do custom stuff using AWS Bedrock, agents using Strands and so on, all the stuff everyone is working with nowadays.

Our facilitator explained how custom rules files can be so very helpful for AI tooling. He linked to this extension with Karpathy-Inspired Claude Code Guidelines as an example. Apparently this plugin is very popular! Yesterday morning the project had 3.5K stars and at the end of the day this already increased to 3.9K. That’s a lot of stars.

I went on to investigate what this extension actually does and found that it’s just one Markdown file of 65 lines long that lays out four principles; the first one is “Think Before Coding”, added with some packaging to make it install in Claude Code.

Publishing it as a Cursor extension

But I don’t use Claude Code, so I fired up Codex CLI and turned it into an extension for VS Code and for Cursor, which is a fork of VS Code but uses a plugin registry from the Eclipse Foundation.

Getting the plugins published was the most work. On the ‘VS Code Marketplace’ I am not a Verified Publisher meaning I do not get a green check mark next to my name, and you will get a warning if you want to install my extension. And apparently the only way to get rid of that is to wait for six months with at least one extension published and then apply for verification. So starting August I can apply for that and any new extensions get automatically trusted.

For Cursor the process felt very cumbersome: I had to create an account on open-vsx.org, create an Eclipse Foundation account, link those accounts, link to my GitHub account, sign an Eclipse agreement, and finally create a GitHub Issue to ‘claim’ my VS Code Marketplace namespace.

Using the extension

So, what does using the extension actually feel like? Because of the non-deterministic nature of these models, I found it hard to tell. I tried a simple refactoring, and I had the idea that it was very reluctant in making changes. Was the result better? I’m not really sure.

Typically, your Cursor rules would list the constraints for your environment, explaining what coding standards to adhere to, architectural constraints and so on. I get that, it makes sense.

I find it wild to think that a company spends millions and millions of dollars on training a model, with tons of engineers meticulously improving output, and then some guy comes along and writes 60 lines of text including Think before coding in the rules and that would make all the difference.

But the original repository has almost 4,000 stars, and surely, 4,000 developers can’t be wrong?

Please try for yourself! Install the extension, don’t forget to star my repository and see the results.

As Paul Simon wrote: These are the days of miracle and wonder!

Discussion on Hacker News

My issues with ProtonMail

2026-02-05T21:21:00+01:00

I use my own domain for email, which I’d recommend to everyone. I was on a cheap Hetzner ‘web hosting with email’ plan before, which wasn’t ideal. During last November’s Black Friday sales I got a ProtonMail subscription and moved my domain there. But I’ve run into several issues, some with how their product works, others specific to my setup.

Can not open some mails on mobile

A small percentage of emails simply won’t open on iOS. When I tap them, the app briefly shows the subject, then closes. I can’t read the content. These same emails work fine in the web interface.

This is a serious problem: your mail client should be able to read mail! I haven’t been burned yet, but I worry about the day I need to show a boarding pass or concert ticket at the door and can’t open it.

I realized there is a workaround for this: opening the web interface in my mobile browser, but that’s far from ideal. ProtonMail has confirmed the issue and says they’re working on a fix.

Mail spoof warning does not show in mobile app

My employer recently switched payroll providers. ProtonMail warns that their mail server isn’t properly configured and the messages could be spoofed, yet coworkers on Gmail or Outlook see no such warning. After checking with our security officer, we concluded the mails are valid and ProtonMail is being overly cautious.

The strange part: this warning only appears in the web interface, not the iOS app, or on the Android app.

If there were an actual spoofing attempt, I’d want to know, especially on mobile! I’ve raised this issue with Proton support.

Mail read flags do not seem to sync between mobile and desktop

Emails I’ve read on my phone sometimes show up as unread in webmail later. Others on Reddit report the same thing, and Proton has confirmed they’re investigating. This is table-stakes stuff for a mail client.

Pulsating menu in ProtonMail

When I open the context menu in a message, it ‘pulsates’. A minor issue, but it’s been there for over two months, testament to the lack of polish in their apps. This only happens on iOS; a co-worker on Android doesn’t see it.

No third party mobile clients

ProtonMail encrypts all data at rest and decrypts on your device. Nice in theory, but it means no standard IMAP, so you can’t use your favorite mail client directly.

The workaround is installing the ProtonMail Bridge on your laptop, which decrypts locally and exposes IMAP for Thunderbird, Outlook, etc. But this doesn’t work on mobile. There you’re stuck with their app or the web interface.

I use Linux with ProtonMail in a browser tab; I don’t love the Bridge approach.

No instant search in webmail without local indexing

Another consequence of client-side decryption: search doesn’t just work. For full-text search, your browser has to download and index all your mail locally. This takes a long time initially.

Conclusion

I really want to love ProtonMail. They’re steward-owned, privacy-focused, European, and building out a full suite of products (VPN, calendar, etc.). But their core product is email, and it has too many rough edges. I expected better from a company that’s been around this long and is this popular. I’ll be migrating elsewhere soon.

That said, most of my issues are with the iOS app. Android users likely have a better experience.

Reinout van Rees on prefect.io

2026-01-22T21:00:00+01:00

Reinout is a long-time visitor of the Python Leiden meetup. In fact, he is a regular on most nearby Python meetups and conferences. The nice thing is that he also writes summaries of the talks he attends and he publishes those on his blog. I really appreciate this! Today he gave a talk at our meetup, and I decided to ‘return the favour’ so here is my summary of his talk!

Reinout discusses prefect.io: it is a server that provides a dashboard, has an API, shows workflows, and allows you to start/restart jobs, examine logs, and such.

In his company much IT-related work involves loading data from web APIs, transforming it in some form, loading it in databases and so on.

Previously this was all done on the command line and people had to log in over SSH and there were constraints about rotating ssh keys which all made it very cumbersome. Now they have a nice web UI and not so much IT restraints and it’s much easier for people because they can just log in to a web UI and click around.

In Prefect, workflows are defined. Workflows consists of one or more tasks. Those tasks are written in python. Prefect comes with some niceties to configure retries on your tasks, it provides a custom logging framework and a lot more. In the UI you can manually start jobs, configure workers, and monitor progress.

Prefect does not provide its own authentication mechanism at the moment. So if you want to ‘protect’ it people are using HTTP Basic auth.

It comes with a docker setup, which is what Reinout is using. Also a hosted version is available.

Reinout created a cookiecutter template that allows non-programmers to create simple python tasks. This has built in workflow that creates a github repository, and configures github actions that creates docker containers on every commit on main, and pushes those to a docker registry.

He uses ‘watchtower’ in the docker compose setup, which allows him to simply deploy the stack once, and the stack will poll for updated containers and keep itself up to date.

I think it’s nice to see that they are able to provide a frictionless way to set up, deploy and monitor data jobs for people who are more data-minded and not hardcore sofware developers!

JPEG XL Test Page

2026-01-21T17:30:00+01:00

This page shows a JPEG XL image, if your browser can handle it! At this point in time (January 2026) this more or less means only Safari will display the image, as far as I know. See also Can I Use.

The person in the image is Jon Sneyers, co-author of the JPEG XL spec and also creator of the “Free Lossless Image Format” that came before it.

I find JPEG XL interesting because of its history. It once was implemented in Chrome, but hidden behind a feature flag. Then Chrome said that it did not saw enough usage, which is unsurprising, really, and it was removed. Now they blessed it again and are re-adding it! Some of this story is found on the JPEG XL Wikipedia page