Part 2: Functional Block Design — The Methodology

In Part 1, we identified the problem: vibe coding collapses when projects grow beyond a handful of features. We discovered the core insight: AI thinks in functions, not systems.

Now we need a methodology.

This part introduces Functional Block Design (FBD) — a repeatable, four-phase process for building systems from AI-generated blocks.

Phase 1: Decomposition — Break the system into functional blocks.

Phase 2: Block Specs — Write a Description (for humans) and a Prompt (for AI) in each .py file header.

Phase 3: Generation — Generate code from the Prompt.

Phase 4: Integration — Connect the blocks into a working system.

We use Python as the example language. One functional block = one .py file. Each .py file contains a header (Description + Prompt) and the generated code below.

Let us walk through each phase using a URL shortener as our running example.

2.1 Phase 1: Decomposition

Goal: Break the system into functional blocks.…