Mastering Spec-Driven Development: Key Questions Answered
In the rapidly evolving world of AI-assisted coding, developers face a choice between spontaneous "vibe coding" and a more structured approach called spec-driven development (SDD). While vibe coding can be fun for weekend projects, it often leads to technical debt and hidden bugs. SDD offers a disciplined yet flexible alternative, leveraging specifications as a source of truth to guide AI agents and human developers alike. Below, we answer common questions about these approaches and how SDD can help you build better software.
What is vibe coding and why is it risky?
Vibe coding is a term coined by AI researcher Andrej Karpathy in early 2025. It describes a coding style where developers rely heavily on large language models (LLMs) like Cursor Composer with Sonnet, accepting all suggestions without reading diffs, and simply pasting error messages back into the AI. While this can produce quick results for throwaway projects, Karpathy himself admits it "mostly works." The risks include hidden bugs, accumulating technical debt, and reduced productivity when a human must later clean up the mess. For serious software, vibe coding is folly—it creates a fragile codebase that can collapse under maintenance pressure.
What is spec-driven development (SDD)?
Spec-driven development (SDD) is a lightweight methodology that avoids the chaos of vibe coding without returning to fully manual coding. Unlike waterfall-style exhaustive requirements, SDD uses concise, readable specifications that act as "version control for your thinking," as Den Delimarsky of Microsoft puts it. A spec defines how code should behave—a contract between developers, AI agents, and testing tools. This contract becomes the source of truth, reducing guesswork and surprises. The result is higher-quality code generated with fewer iterations. SDD is not about planning everything upfront; it's about creating a clear, shared understanding that both humans and AI can follow.
How does Spec Kit enable spec-driven development?
Introduced by Den Delimarsky, Spec Kit is a tool that formalizes SDD practices. It treats a spec like code, putting it under version control so teams can track changes in thinking as the project evolves. Spec Kit integrates with AI agents, allowing them to read the spec, generate code that matches the contract, and validate outputs against the spec automatically. This reduces the back-and-forth typical of vibe coding. By making the spec a living document, Spec Kit ensures that both human developers and LLMs stay aligned, decreasing the likelihood of hidden bugs and cutting down on cleanup time.
What are the benefits of SDD over vibe coding?
The primary benefit of spec-driven development is reliability. While vibe coding can produce code quickly, it often generates technical debt that requires more time to fix than writing code manually. SDD reduces this debt by defining clear behavioral boundaries from the start. Developers spend less time debugging and more time on design. Additionally, SDD scales better for team projects—multiple contributors and AI agents can work from the same contract, avoiding conflicts. SDD also makes it easier to test outcomes, since the spec provides expected behaviors. Though it requires some upfront thinking, the long-term savings in maintenance and rework are substantial.
How does Birgitta Böckeler at Thoughtworks view specs?
Birgitta Böckeler has written extensively on how to divide specifications effectively. She advocates for splitting specs into small, focused chunks that map directly to user stories or features. Each chunk should be testable independently, making it easier for developers and LLMs to implement without scope creep. Böckeler emphasizes collaboration—team members review and refine specs together, treating them as communication tools rather than static documents. This aligns with SDD's principle of keeping specs concise and readable. Her approach helps teams avoid the trap of over-specification while still providing enough detail to guide AI code generation reliably.
Can SDD work for weekend projects or is it only for serious software?
While vibe coding is often marketed as ideal for quick, throwaway projects, SDD can be adapted to any scale. For a weekend project, you might write a one-paragraph spec defining core behaviors rather than full system architecture. Tools like Spec Kit allow you to keep it lightweight. The advantage is that even a small spec prevents the "mostly works" syndrome—your code will behave predictably. And if the project grows, you already have a foundation. Many developers find that spending 10 minutes writing a spec saves hours of debugging later. SDD doesn't mean abandoning speed; it means investing a little upfront to avoid rework.
How do I get started with spec-driven development?
Start by adopting a simple workflow: write a short spec for your next feature using markdown or a tool like Spec Kit. Define the input, expected behavior, and error handling. Then feed that spec into an LLM as context. Generate code in small increments, validating against the spec after each change. Over time, you can evolve your spec style to include test cases and acceptance criteria. One practical tip: keep specs under version control so you can track how your understanding changes. Eventually, you'll build a library of specs that speed up future development. SDD is a skill—start small, and you'll see the benefits compound.