Phase 1: Spec-Driven Development · 40 min · Claude Code · Python

Why Specs Before Code

A spec written after the code just describes the bug. A spec written before the code can catch it.

What you will learn

Explain the root problem spec-driven development solves: drift and hallucination in AI-assisted codebases
Contrast the traditional think -> code -> document loop with the specify -> generate -> validate loop
Demonstrate concretely why documentation written after the code can't catch bugs the code already contains
Identify when a team's 'documentation' is actually just a restatement of current behavior rather than an independent spec

Introduction

Why Specs Before Code

Objective

Prove concretely that a docstring derived from reading buggy code cannot catch its own bug, while an independent spec written from the business requirement can.

Unlock the full lesson

You've read the first 2 sections. The rest of this lesson covers The Problem, The Concept, Build, Check Yourself, Key Terms & Next — plus a hands-on lab, quiz, and project artifact.

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