Four Agent Frameworks in Sixteen Months
How Gama went from LangChain to LangGraph to Google ADK to Mastra to the Claude Agent SDK — and what we'd tell our December 2024 selves.
Sebastien Castiel | Articles
Developer, writer, indie hacker · 📍 Montreal, QC
Latest posts
If Claude Writes the Code, What Makes Me Still a Developer?
It's been three months since I last wrote a line of code.
Watching, Not Waiting: When AI Coding Crossed the Speed Threshold
I know that feedback about using AI as a dev is so mid-2025, but I feel there are still some things to say.
Designing AI‑Ready Systems: Making Code Easy for Assistants
Most leverage from AI doesn't come from writing AI code—it comes from writing code that AI can use. When your system exposes clear contracts and examples, assistants can extend it safely.
Building a Modular AI Copilot: From Monolithic to Dynamic Context
How we built Vasco's Copilot — from a LangChain-and-Gemini prototype to a modular architecture where each page declares its own context and tools.
Seven Hours, Zero Internet, and Local AI Coding at 40,000 Feet
Seven hours on a plane, zero internet, and a curiosity about local AI coding. That's how I found myself downloading 13GB of AI models in an airport lounge, preparing for what would become an accidental experiment in offline…
AI-Assisted Development: A Three-Act Play
Developers on my team use Cursor's Tab feature. Designers use vibe-coded prototypes to gather feedback from stakeholders. I rely on Claude Code to plan and build larger features. Same AI technology, completely different…
Turning Claude Code Into My Best Design Partner
When I first started using Claude Code, I had a naive approach to working with it. I would describe the task directly in the prompt, press Enter, and cross my fingers. If the agent made mistakes, I would tell it how to fix them.…
Two Hours with Cursor Changed My Mind About AI Coding
For the first time in my career, I have absolutely no idea what the software engineer job will look like in five or ten years.
Spliit by the Stats: Usage, Costs, Donations
A transparency report on Spliit's first year, sharing figures on visits and usage, the roughly $115 monthly hosting costs, the donations that nearly cover them, and how much time goes into the project.
Spliit Is Now Available in Eight Languages
Thanks to open-source contributors from around the world, Spliit now supports eight languages, and this post credits the people who added each translation and invites others to contribute.
We Need an Open Source Alternative to Splitwise
After Splitwise began limiting free usage in late 2023, this post argues that a widely used app should be more than just free, and explains why building Spliit as an open source project guarantees users can keep using it freely forever.
Announcing Receipt Scanning Using AI
Spliit now lets you create an expense by taking a photo of a receipt, using OpenAI's GPT-4 with Vision to automatically extract the title, category, amount, and date.
13 tips for better Pull Requests and Code Review
Would you like to become better at crafting pull requests and reviewing code? Here are the 13 tips from my latest book that you can use in your daily developer activity.
The simplest example to understand Server Actions in Next.js
Server Actions are a new feature in Next.js. The first time I heard about them, they didn’t seem very intuitive to me. Now that I’m a bit more used to them, let me contribute to making them easier to understand.
Intro to React Server Components and Actions with Next.js
React is living something these days. Although it was created as a client UI library, it can now be used to generate almost everything from the server. And we get a lot from this change, especially when coupled with Next.js. Let’s use Server Components and Actions to build something fun: a guestbook.
How to give code review as a junior developer?
By focusing on learning, providing constructive feedback with a positive tone, and embracing the opportunity to contribute, junior developers can make valuable contributions to code quality and their own growth. Code reviews are essential for skill development and fostering collaboration within development teams.
How well should I know React before applying to my first job?
A recurring question I hear from people learning React: “how do I know if I’m ready to apply to junior React developer jobs?”. Very often, they’re ready before they know.
A better learning path for React with server components
What if we took advantage of React Server Components not only to improve how we use React, but also how we help people learn it from the beginning?
Display a view counter on your blog with React Server Components
A short tutorial with a cool use case for React Server Components, Streaming and Suspense with Next.js: adding a view counter on a blog, calling the Plausible analytics API.
Using Zod & TypeScript for more than user input validation
If you have ever created an API or a form accepting user input, you know what data validation is, and how tedious it can be. Fortunately, libraries can help us, such as Yup or Zod. But recently, I realized that these libraries allow patterns that go much farther than input validation. In this post, I’ll show you why I now use them in most of my TypeScript projects.
Display your Gumroad products on your Next.js website
If you sell some products on Gumroad and also have a personal website, maybe you’d like to automatically list your products on this website. And if your website is based on Next.js, you can do it pretty easilly using Gumroad API.
Use Next.js Image component in posts with Markdown
Next.js has a wonderful Image component that lazy loads images and optimizes their dimensions. Here is how to use it when generating your blog from Markdown.
Create OG images for your blog with Next.js
Vercel recently announced a new library to generate OpenGraph (OG) images. A short tutorial to see how to use it to generate OG images for your Next.js application.
Combining scripts and DSLs is Kotlin’s most underrated feature
The more I play with Kotlin, the more convinced I am that a combo of two of its features is vastly underrated: first, the ability to create domain-specific languages (DSL), thanks to some syntactic sugar; then, the ability to write scripts and create interpreters for them.
Walk in the steps of successful makers, and fail
Following advice by successful people might not be enough. A short essay about survivorship bias, and how it can make you forget the most important ingredient to success: luck.
Purchasing Power Parity: fair pricing for your SaaS product
Using Purchasing Power Parity, you can offer a fair pricing based on your user’s location. Here I explain what it is, then I show you how I implemented it on my course’s selling page using serverless functions and a little bit of React.
How I use Pandoc to create programming eBooks
Here is the story of how I built my eBooks, especially the last one. After some trial and errors, in the end, I used the same recipe as the two previous ones, and it involves a fantastic tool: Pandoc.
Reimplement Redux with vanilla React in 12 lines of code
Redux is an awesome library to handle the state of big applications, React or not. But when you think about it, the basic features of Redux can be implemented in very few lines of code. Let’s see how.
Understand how React hooks work
The reason hooks cause developers to struggle is that they look simple, just basic functions, but they are a lot more complex than that. The complex logic is very well hidden in the React core, but understanding a little how they work will help you to use them at their full potential, and overcome the issues you face more easily.
Back to basics with Node.js and Express, the time of a side project
Although I love React and am more used to single-page applications (SPA), I decided to leave them aside the time of a side project and to use plain old Node.js, Express, Pug, and MongoDB. And that felt good!
Why you should have side projects
As a developer, you may have acquired some skills that you don’t find the time to practice. Or you may want to learn new ones, but your daily job doesn’t give you the opportunity. Side projects are an excellent way to solve these problems.
Create an animated 3D book in CSS, step by step
A couple of days ago, I created a 3D version for the book I’m writing, with CSS only. Because I couldn’t find an easy way to do it, I created a small 3D book image CSS generator. There was a lot of interest for it, and since it’s definitely not that complicated, here is a small tutorial to learn how to create your own version.
On distraction and developer productivity
When twenty developers were asked to keep a precise diary of what tasks they worked on during the day minute by minute, the results were surprising. Maybe you don’t code as much as you think you do during a day…
I’m writing a new book: Become an Outstanding Developer
When you’ve been working as a developer for several years, improving at coding is not enough to become better at your job. Of course, it’s a very important thing, but some soft-skills can make you not only better but one of the best. And I decided to accept the challenge: explore them and put them into a book!
I tried Flutter for a week and made an app
It’s been some time that I hear about Flutter, the UI library by Google supposed to be a concurrent for React. I’m a huge fan of React, and on the paper Flutter has all the arguments. And that made me want to try, so last week I decided to learn Flutter by making a small iOS application.
Create a React hook to add dark theme to your app
Thanks to a recent evolution in mobile and desktop operating systems, it is more and more common for users to expect two UI themes for apps and websites: a light one and a dark one. In this article we’ll see how it is possible to offer two themes in your React application, using the one the user prefers by default.
This blog is proudly powered by Gatsby (with some super powers)
This blog has been using Gastby for a year now. Before that I used a home-made tool I was proud of, but it was very minimalistic. Switching to Gastby was a very interesting thing to do, it’s a fantastic tool, but let’s be honest, it’s quite hard to use. I made a lot of improvements on the codebase of this blog these past few days, here is a small feedback.
Beginner Guide to Deep Work for Developers
Have you ever dreamed to wake up one morning and realize you felt different, more powerful. As if you had this super power inside of you that it waiting to be used. Good news: as a developer, you do have this super power.
One year as a morning person
I’ve been living in Montréal for almost two years now. I’m currently going in vacation in France to see friends and family, for the fifth time in these two years. Montréal is not that far from France. You take off on the evening, and you arrive early on the morning. (Short night though.) For the return it’s even shorter: you land only a couple hours after taking off, thanks to the time shift.
Lost with Redux and sagas? Implement them yourself!
You can use everyday a library such as React, Redux or Redux-Saga. You can be perfectly efficient with it. You can be able to tell others why it is nice or not, and wether they should use it or not. But at the same time it’s possible you consider it a bit magic.
React hooks: get the current state, back to the future
React Hooks are trully awesome, but the more I play with them the more I discover tricks, and sometimes spend a lot of time figuring out why my code doesn’t do what it is supposed to.
So I wrote a technical book 😁
Big week for me: I finished writing my eBook in French about React, and I couldn’t be prouder. Eight months, and it was not easy, but it’s so worth it. In this post I wanted to expose a few thoughts about what happens when you write a technical book.
Est-il utile d’apprendre React ?
Plusieurs tweets m’ont interpelé récemment, par rapport au fait que l’écosystème JavaScript s’est dégradé, car concentré autour de plus en plus d’outils pas forcément utiles. React en prend notamment pour son grade.
Pourquoi j’écris un livre sur React ?
Voilà quelques mois, j’étais à la recherche d’un nouveau projet personnel. Bien souvent ce type de recherche aboutit au développement d’une nouvelle application web ou mobile, mais cette fois-ci, j’ai plutôt décidé d’écrire un livre. Ce n’est pas la première fois, j’avais écrit un livre consacré à Node.js en 2013. Le projet m’avait beaucoup plu, bien que cela prenne beaucoup de temps.
Bootstrap a Reason-React project with Parcel
Not that long ago I used Create-React-App a lot to quickly boostrap my React projects. That’s why I naturally used Reason Scripts when I wanted to use Reason-React. But even if I still understand the advantages of the approach of CRA and Reason Scripts, I recently discovered Parcel, a very minimalist bundler for web projects.
Create reusable high-order React components with Recompose
Writing reusable components in React is something every React developer care about (or should care about). Wether it’s to create a toolbox of styled components, to mutualize common behaviors, etc.
Create a simple and tested Redux-like app with Reason React
In the past few weeks I’ve become a big fan of Reason, and in particular its association to React with Reason React. And because both Reason and Reason React are really young projects, there is not a lot of tutorials, StackOverflow questions, and documentation about it yet. So beginning a new project isn’t as easy as the official website wants us think.
Writing modern JavaScript code
Remember when JavaScript was a language used to make elements change on the page when the cursor was over them? These days are over, every language evolves over time, and so does the way wa use them. Look at the code you wrote one or two years ago: do you feel ashamed? If yes, this post is for you 🙂
Play with cryptography with OpenPGP.js
For about a year now, I use ProtonMail as my mail provider. If you don’t know it, you should definitively give it a look! The mails are encrypted _end-to-end_, which means that ProtonMail has absolutely no readable version of the stored emails, nor any key to decrypt them.