Book 3: Water Tracker Overview

What Is Offer Driven Development?

Most builders fall into the same trap: they build first, then try to sell. A weekend goes into an app. It works. It looks clean. And then nothing. A handful of downloads. Zero paying customers. The cycle starts again.

AI coding tools have made this worse, not better. Claude Code, OpenAI Codex, Gemini CLI: any of them can ship a working app in a day. That speed is brilliant. It is also dangerous. Speed without direction just means you build the wrong thing faster.

Offer Driven Development (ODD) flips the sequence. Instead of build then sell, you sell then build.

Before you write a line of code, you define the offer. What transformation are you promising? Who is it for? What will they pay? Then you ask ten people if they would pay for it. Not “do you think this is a good idea?” (everyone says yes to that). “Would you pay for this?” That question gets honest answers.

If seven out of ten say yes, you build. If three say yes, you fix the offer. If zero say yes, you have saved yourself a wasted weekend.

This is the third book in the series. You have already seen ODD applied to a Sleep Tracker with Claude Code (Book 1) and a Time Boxing app with OpenAI Codex (Book 2). The methodology is identical. The tool and the project are different.

The VOSS Framework

ODD is the philosophy. VOSS is the system that makes it work. Four stages, each building on the last:

Vault. Structure your knowledge in Obsidian. Your skills, stories, and expertise go into a structured vault that feeds everything after it.
Offer. Sell a digital product that describes the offer in detail to 10 early adopters on Gumroad. Score it using the Hormozi Value Equation. The goal: ten people pay before you build anything. That is proof your idea has legs.
Ship. Build and deliver using SpecKit. You only build what the offer requires. Nothing more. This constraint prevents feature creep.
Scale. Grow beyond the 10 with outreach. Warm outreach, social content, and selling skills turn ten early customers into a real business.

In this Book Lab, the VOSS framework is not a separate set of guides. Each stage has its own dedicated page, tailored to the Water Tracker project you are building.

What You Will Build

You will build a Water Tracker mobile application using Gemini CLI as your AI coding partner. The app helps users set a daily hydration goal, log every glass of water throughout the day, and visualise their habits over weeks and months.

The app has five screens:

Home: a progress ring showing today’s intake against the daily goal, quick-add buttons (+100ml, +250ml, +500ml), a custom amount button, and a streak counter
Daily: a chronological list of today’s individual water entries with timestamps and running totals
Weekly: a 7-day bar chart of daily totals with a horizontal goal line and weekly average
Monthly: a calendar heat map of the current month, colour-coded by goal achievement (green for met, amber for over 50%, red for under 50%)
Settings: configurable daily goal, unit preference (ml or oz), and reminder intervals

The app tracks water intake in millilitres with a configurable daily goal. Everything stays on your phone. No account. No cloud. No wearable required.

This is the third and final book in the series. You have already built a Sleep Tracker with Claude Code (Book 1) and a Time Boxing app with OpenAI Codex (Book 2). By the end of this series you will know how all three major AI coding tools handle the same process, so you can pick the one that suits you best.

The water tracker is a teaching vehicle. What you are learning is the ability to build and sell any digital product, with any AI tool, for any audience. The methodology is the product. The app is the proof that it works.

What Are Skills?

Throughout this Book Lab you will see references to skills. These are pre-written instruction files that give your AI coding tool specialised knowledge about a particular task. For example, the vault-validator skill knows the exact folder structure, required files, and YAML frontmatter rules for a CoEngineers vault. The offer-validator skill knows how to score your offer against the Hormozi Value Equation.

Skills auto-activate when you describe a task in plain language. If you type “validate my vault,” the vault-validator skill kicks in automatically. If you type “score my offer,” the offer-validator skill takes over.

You need to download the skills starter before starting — the Prerequisites page has the download links for each AI tool.

Your Learning Path

Each page in this Book Lab follows a stage of the VOSS framework:

Page	VOSS Stage	What You Will Do
Vault	Vault	Set up your Obsidian vault for the Water Tracker project
Offer	Offer	Define, validate, and sell your offer to 10 early adopters
Ship	Ship	Build the Water Tracker app using Gemini CLI and SpecKit
Scale	Scale	Grow beyond your first 10 with outreach and content

What Comes Next

Head to the Vault page to set up your Obsidian vault for the Water Tracker project. This is the first stage of the VOSS framework and takes approximately 30 minutes with your LLM.