Blog - felix-arntz.me

10 Lessons from 10 Years of Contributing to WordPress Core

June 29, 2025

Today marks a special anniversary for me: It has been exactly 10 years since I received my first props for a contribution to WordPress Core. And it was just a day before that I actually worked on that first contribution.

You may know that I am a long-term WordPress Core contributor, having contributed ever since. To celebrate this 10-year milestone, I wanted to reflect on this journey and share the 10 most valuable lessons I learned along the way. But first, let me provide a bit of background about just how I started.

Migrating Your JavaScript Codebase to TypeScript with Cline & Gemini

June 19, 2025

I recently undertook a significant project: migrating the entire JavaScript codebase of my AI Services plugin for WordPress (GitHub repository) to TypeScript.

Why is that significant?

We’re talking about over 80 JavaScript files, so it’s by no means a small project. Not gigantic like e.g. Gutenberg, but certainly a substantial amount of code.
Additionally, that JavaScript code is powering a plugin with a fairly unique feature set. This uniqueness often makes it harder for Large Language Models (LLMs) to assist, as there’s likely less similar code in their training data.

The process taught me a lot about the synergy between a well-structured codebase and LLMs. It also strengthened my belief that, while an LLM isn’t magically going to solve complex development tasks for you, it can be a massive productivity booster when you prepare your project and guide it effectively.

This post will walk you through how I used Cline in VS Code together with Google’s Gemini models to get it done efficiently and why I think this migration was worthwhile.

Introducing the View Transitions Plugin for WordPress

June 4, 2025

I’m thrilled to announce a new plugin from the WordPress Core Performance Team: View Transitions! This experimental plugin brings the power of the cross-document View Transitions browser API to your WordPress site, allowing for smoother, animated transitions between page navigations.

View Transitions?

Traditionally, moving from one page (or, technically, URL) to another on the web has always involved an abrupt, “hard” reload. While this might seem completely natural to many of us on the web, user expectations have shifted drastically in the past (almost) two decades.

Native mobile applications, with their seamless in-app navigations and smooth transitions, have set a new bar for user experience. This has led web developers to try to catch up with that experience, often turning to Single Page Applications (SPAs). While SPAs aim to mimic native app navigations by dynamically updating content without full page reloads, this often comes with increased development complexity and a shift in how you structure your entire website, often at the cost of accessibility or performance.

Now, with cross-document view transitions, you can achieve that desired user experience through smooth transitions on the web without any extensive overhaul of your website. And the new View Transitions plugin makes it super simple in WordPress.

Speculative Loading, or A Brief History of Landing a Performance Feature in WordPress Core

May 22, 2025

Two years ago today, on May 22, 2023, I opened an experimental pull request for a new module in the Performance Lab plugin. That little experiment was the very first step on a long road that ultimately led to the “Speculative Loading” feature landing in WordPress 6.8 last month (April 2025).

For those unfamiliar, the Speculative Loading feature enhances performance by speculatively loading pages a user is likely to visit next, which can make navigation feel almost instantaneous. If you want to dive into the technical nitty-gritty, I recommend checking out the “dev note” post on Make WordPress Core.

This post, however, isn’t about the what or how of the feature itself. Instead, I want to pull back the curtain and share the story behind the feature—the milestones, the discussions, and the collaborative effort that took it from a spark of an idea to a reality for millions of WordPress sites. The impact is considerable even for the entire web. Keep reading to the end for concrete numbers. 👇

Deploying Your WordPress Plugin’s “Tested Up To” Version Bump in Isolation

May 8, 2025

Keeping the “Tested Up To” version of your WordPress plugin up-to-date on WordPress.org is crucial for ensuring compatibility and giving your users confidence. However, the process of manually updating this information can be a bit tedious, often involving a new release even if no other code changes are necessary.

While there are existing GitHub Actions that can deploy plugin assets to WordPress.org, such as the excellent 10up/action-wordpress-plugin-asset-update, using them solely for updating the “Tested Up To” version without any customization can be less than ideal. You might inadvertently deploy other changes you’ve made to your readme.txt file or other assets, even if those weren’t intended for immediate release. This could lead to unexpected updates on the plugin directory.

Imagine you implemented a new plugin feature in your GitHub repository which is not released yet, and you’ve already included documentation about it in the readme.txt. You wouldn’t want that to be deployed by accident when all you want to do is bump the “Tested Up To” version.

This post highlights a targeted GitHub workflow for exactly this purpose, which allows you to automate the deployment of bumping your WordPress plugin’s “Tested Up To” version in isolation.

My mom’s Vanillekipferl recipe (the best German Christmas cookies)

December 6, 2024

The other week we were hanging out with our friends K. Adam and Emily, and K. Adam shared with us some delicious Italian cookies he had made. Their texture and almond flavor reminded me of my favorite German Christmas cookies, called “Vanillekipferl”. Maybe you’ve seen them or even had them before – they’re half moon-shaped cookies with somewhat crumbly dough, usually topped with powdered sugar (or “snow”).

Vanillekipferl have been a staple in my life for as long as I can remember, and every Christmas I would eat far too many of them. Every Christmas I would love to come home to my parents and eat my mom’s Vanillekipferl. But when I moved to the US and then COVID hit, gone was my ability to go home for Christmas – which is when I made them myself (or rather, with my then-girlfriend, now wife 😊) for the first time and asked my mom for the recipe. They were and still are my favorite Christmas cookies after all.

So as we were talking about the cookies the other week, K. Adam asked me for the recipe for Vanillekipferl, but all the instructions I had were in German, and also were missing some explanations that my mom had just told me in addition. This led me to think that I should write down this recipe, in English, with all the ingredients and amounts and temperatures translated too. To share them with others of course, but even to help myself when I make them here in the US – yay for the imperial system. 😂

So in this post I’m sharing with you my mom’s recipe for my favorite Vanillekipferl.

Writing a WordPress plugin to generate image alt text with AI Services

October 23, 2024

In my initial post that announced the AI Services plugin for WordPress I mentioned several times how it simplifies using AI in WordPress by providing AI service abstractions as central infrastructure.

In this post, let’s take a more hands-on look how you as a developer can use the AI Services plugin: We will write a WordPress plugin that generates alternative text for images in the block editor – a crucial aspect of good accessibility, which AI can be quite helpful with. Since the feature will be built on top of the AI Services plugin, it will work with Anthropic, Google, OpenAI – or any other AI service that you may want to use. And the entire plugin will consist of less than 200 lines of code – most of which will in fact be for the plugin’s UI.

Introducing the AI Services plugin for WordPress

October 9, 2024

It’s safe to say the topic of generative AI doesn’t need an introduction in today’s age. It has been emerging throughout the tech world. However its adoption in the WordPress ecosystem has been slower than in other ecosystems. This is for various, mostly technical reasons that make implementing generative AI features in WordPress harder than elsewhere.

That’s what I’m trying to address with AI Services, a new free open-source plugin that is now available for early access on GitHub, and as an early version 0.1.0 in the WordPress plugin directory.

AI Services is an infrastructure plugin which makes AI centrally available in WordPress, whether via PHP, REST API, JavaScript, or WP-CLI – for any provider. Other plugins can make use of the APIs from the AI Services plugin to easily add AI capabilities to their own plugins, for whichever third party service they prefer: Whether it’s Anthropic, Google, or OpenAI, whether you’d like to use another service, or whether you’d like to leave the choice up to the end users of your plugin – AI Services makes it possible by providing access to the various APIs in a uniform way. It acts as a central hub for integrating AI services, allowing plugin developers to focus on functionality instead of managing individual service integrations. As an end user of WordPress, that means you have more control on how you would like to use the AI capabilities provided by the plugins.

Autoloading WordPress options efficiently and responsibly

October 1, 2024

If you’re a WordPress plugin developer, you may have come across the concept of autoloading options. Or you may not, since knowing about autoloading options is, technically speaking, entirely optional when implementing a WordPress plugin that uses options. However, being unaware of the concept of autoloading options can lead to massive performance problems for large WordPress sites. It can notably slow down the server response of sites using your plugin. And by doing that, it hurts their “Time to First Byte” (TTFB), which directly contributes to the Core Web Vitals metric “Largest Contentful Paint” (LCP).

This post is about explaining what autoloading options in WordPress is, how it works, and how plugins should go about it. We’ll go over the basics as well as explore how to use more recently introduced WordPress Core enhancements, including some code examples. This will hopefully help you get to a comprehensive understanding of how to apply autoloading in your WordPress plugins in a way that’s both efficient (for your own plugin’s usage) and responsible (for the overall sites using your plugin, in a gazillion of combinations with other plugins).

My WordPress Core Contribution Workflow

September 22, 2024

During an informal meetup between the WordPress Core committers attending WordCamp US 2024, one of the topics we discussed was how each of us was handling commits. Given that WordPress Core uses svn and Trac for its source of truth but git and GitHub are encouraged for contributing, it can be a bit of a hassle to synchronize changes when it comes to committing code to WordPress Core.

Fortunately, this is only relevant for the folks that commit code, i.e. nothing that a new contributor needs to worry about. Yet, there’s a good number of committers, and new ones are added regularly, so we thought it would be good to document our workflows. There’s no “official” documentation about this, simply because there’s no universally recommended approach. Many committers have come up with their own solutions throughout the years, so we decided it would be a great idea if each committer documented their approach, so that we would have a number of solutions to compare and for newer committers to review and choose from.

This brief article outlines my personal workflow for committing to WordPress Core.