A Leaner JustInterval: Moving From Firebase Studio to Local AI

By Magne · August 22, 2026 · Development & Training

JustInterval has always been two things at once: a practical timer for structured spin sessions and a small laboratory where I can learn by building. This summer, both parts of that story changed.

The app has moved out of Firebase Studio and into a local development setup. At the same time, I have removed many of the features that accumulated around the original timer. The result is a smaller, more focused JustInterval that is easier to understand, maintain, and use in a class.

Firebase Studio is closing

Google has announced that Firebase Studio will shut down on March 22, 2027. Google recommends Google AI Studio for browser-based prototyping and Google Antigravity for a code-first, local workflow.

The shutdown applies to the development environment, not the core Firebase services. JustInterval can therefore continue using Firebase Hosting and Firestore. What had to change was where and how I work on the source code.

Choosing a local development setup

I decided to move the project into Visual Studio Code and keep GitHub as the source of truth. OpenAI Codex now helps me inspect the code, fix bugs, run tests, and manage the deployment workflow.

I have also installed Ollama with Qwen2.5-Coder running directly on my laptop. That gives me a fully local AI option when I want to work without cloud model credits. I can deliberately choose between a cloud Codex session and a local Qwen session while working on the same repository.

A new laptop gave me the final push to set up a proper development environment—not only for JustInterval, but for any personal project where AI and local agents can help me maintain the work over time.

When more features became less useful

The earlier version of JustInterval had accumulated plenty of bells and whistles: an AI Coach powered by Gemini, Bluetooth trainer integration, target-watt controls, advertising, and several supporting screens. Building those features taught me a lot, and the complete history is preserved in GitHub.

In practice, however, the extra features were rarely used. The Gemini API usage behind the AI Coach also introduced an ongoing cost, while every additional integration created more code that needed attention. A feature is not free just because the first version was quick to generate.

So I trimmed the application. The AI Coach and its Gemini keys are gone. Bluetooth control is gone. Advertising is gone. The workout builder no longer asks for target watts. The interface is broader, calmer, and centered on building and running a sequence of timed intervals.

Power still matters

Removing target-watt fields does not mean power has become less important in my coaching philosophy. Quite the opposite: training with a power meter remains one of the cornerstones of how I structure intensity.

But every rider has an individual target. A single number typed into a shared class timer can distract from that reality. The coach can communicate the purpose and intensity of an effort, while each participant works from their own FTP, current capacity, and goals. JustInterval only needs to make the structure unmistakably clear.

Back to the spin class

I recently started a new job at Lighthouse and am back working with Equinor. We are developing many custom solutions, and that has left little spare time for fixing bugs and maintaining this page. The leaner version is partly a response to that reality: a useful small application should be possible to maintain without becoming a second job.

I hope we can continue the spin class this coming winter, and I hope the updated timer works well for the people in the room. I also hope it remains useful beyond our own class. Over time, I have received emails about JustInterval from Australia, China, and Norway. Historical usage data also suggested that the app was surprisingly accessible in China.

That reach is more than I expected from a simple side project. It is also a good reason to keep the page fast, accessible, and free of unnecessary dependencies.

The next version is the simpler one

JustInterval is still a learning project, but the lesson has changed. Earlier, the goal was to discover how many modern capabilities I could connect. Now the goal is to decide what the product can do without.

The old version is safe in Git history. The current version has a clearer purpose: help people build structured intervals, see what comes next, and keep moving.