Weekly newsletter

A different sports app, vibe-coded every week.

I build one small, useful sports tool each week with AI, then tell you honestly how it went: the prompts, what broke and what I fixed.

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The Saturday 5K Pace Planner on a desktop screen: a form asking for a PB, target time, age and age-grading category, with a Plan my 5K button. — Latest build, issue 1: Saturday 5K Pace Planner. Open the tool

The Saturday 5K Pace Planner on a phone: a 57.8% age grade for a 23:45 target and a table of five per-kilometre splits. — Latest build, issue 1: Saturday 5K Pace Planner. Open the tool

Latest build

This week’s build

The Saturday 5K Pace Planner on a phone showing the start of its form: PB time, target time, age and category.

RunningIssue 126 October 2026

Saturday 5K Pace Planner

Enter your 5K time, age and target to get an age-graded percentage, per-km splits for your course and a shareable result card. Works for any 5K, including weekly timed runs.

5K
age grading
pacing

Open the tool Source code

Also available at saturday-5k-pace-planner.vercel.app.

The method

How Sport Builds works

One idea a weekA small sports tool that does one job well, built from a clear brief.
Built with AIVibe-coded in public: real prompts, real tests, a live demo and open source code.
Honest notesEvery issue says what broke and how it was fixed, not just the shiny result.

More builds are on the way, one a week. See the archive.