About 5 years ago, I built a weightlifting app for 5/3/1 that got me on the front page of HN [0]. After that, life happened. I had kids and so decided to get a job and put that project on ice. Eventually I grew too disappointed with my job, and decided to try building something again.

The biggest feedback I kept getting from users was simple: “Let me create my own programs.”

That’s how Vis started.

The initial idea was to create a B2B platform where gyms and trainers could build programs using formulas (e.g., percentages of 1RM) and reusable blocks instead of spreadsheets. I built what I still think is the best workout editor out there, but I quickly found out that B2B sales is hard (or maybe I just suck at it). It also just didn’t feel like a big enough sell for gyms.

So I pivoted. I focused on the iOS app for a while [1], and now re-packaged the editor so individuals can use it directly.

With Vis Pro, you can:

- Define programs using formulas (e.g., 0.85 * SQUAT_1RM, or even better: RPE(8, SET_REPS) * SQUAT_1RM)

- Build workouts by re-using pre-defined or even custom blocks

- Share your programs and workouts with others

The core idea is that programs are parametric instead of static. Change your 1RM and the entire program recalculates automatically.

You can try it out without an account at https://vis.fitness/pro/try/create-program

The whole thing is built with NextJS, using Chevrotain (surprisingly solid) for the formula engine.

It's been super interesting using Codex since late Dec. It's been a huge force multiplier, enabling me to ship really cool features like formula autocomplete and syntax highlighting in a couple of hours. I'm used to reviewing a lot of code from my time at Google, so that hasn't been a problem, but it's interesting to feel that the review speed is now the limiting factor. Though the codebase would become unmaintainable real quick without that.

The next step is building an MCP server to allow users to create programs using LLMs and have them show up directly in the editor (and your phone).

Would love feedback, whether you even lift or not!

[0] https://news.ycombinator.com/item?id=31508009

[1] https://apps.apple.com/us/app/vis-next-generation-workouts/i...