Vibe Coding vs Spec-Driven Development: When to Use Each

Here is the short version, so you do not have to scroll for it. Vibe coding is prompting an AI agent and iterating by feel until the output works. Spec-driven development writes the specification first and treats it as the source of truth that code is derived from. Vibe coding buys you discovery speed. Spec-driven development buys you production durability. They are not rivals. They are different tools for different moments, and the skill in 2026 is knowing which one the task in front of you actually needs.

I am a backend engineer. I spend most of my day building production APIs with AI agents in the loop, and I have shipped things both ways, sometimes badly. This post is the framework I wish I had a year ago, when “just vibe it” and “write a real spec” felt like a personality test instead of an engineering decision.

We have written a lot about the tools you use to do this, from comparing Cursor, Claude Code, and OpenCode to writing CLAUDE.md files. This post is about the method, which matters more than the tool.

The term “vibe coding” has a precise origin. In early February 2025, Andrej Karpathy (a founding member of OpenAI and former Director of AI at Tesla) described “a new kind of coding I call ‘vibe coding’, where you fully give in to the vibes, embrace exponentials, and forget that the code even exists.” He described accepting every diff without reading it and pasting in errors without comment: “I just see stuff, say stuff, run stuff, and copy paste stuff, and it mostly works.”

That post lit the fuse. The rest of 2025 became, as developer Tiago Valverde put it, “a 2025 hot summer of vibe coding.” After that, “the trend is shifting to Spec-Driven Development, after the industry realized that they can't escape planning and solution designing in the AI era.”

The most telling signal came from Karpathy himself. About a year after coining the term, he wrote that “programming via LLM agents is increasingly becoming a default workflow for professionals, except with more oversight and scrutiny,” and that he now prefers the label “agentic engineering”: “the new default is that you are not writing the code directly 99% of the time, you are orchestrating agents who do and acting as oversight.” The New Stack framed it bluntly: vibe coding is passé. The man who named it had moved on.

Vibe coding is a tight loop: write a short prompt, let the agent generate, run it, and adjust by feel until the result looks right. You are not maintaining a mental model of the code. You are reacting to its behavior. The running output is the only thing you trust.

When the stakes are low, this is genuinely the right move. There is no faster way to find out whether an idea has legs, to learn the shape of an unfamiliar library, or to throw together a demo before lunch. Speed is the whole point, and structure would only slow you down.

The trap is not vibe coding itself. The trap is letting a Tuesday-afternoon prototype quietly become the foundation of a production feature, with no one ever stopping to write down what it is supposed to do.

Spec-driven development (SDD) inverts the relationship between code and intent. Instead of code being the artifact and the spec being an afterthought, a structured, versioned specification becomes the source of truth, and the implementation, tests, and documentation are generated and maintained against it. As InfoWorld frames it, the spec anchors the AI rather than letting it free-associate.

In practice, most SDD workflows move through four phases:

This is not just a process; it is now tooling. GitHub's Spec Kit is an open-source, MIT-licensed toolkit that adds a spec-driven workflow to 30+ AI coding agents. Amazon's Kiro is an agentic IDE built around explicit requirements, design, and task phases. Martin Fowler's team has written at length about how these tools make specifications executable rather than decorative.

You do not need a dedicated tool to start, though. A well-written CLAUDE.md or a markdown spec the agent reads before it implements anything is spec-driven development in its simplest honest form.

The two methods optimize for different things. Lined up side by side, the tradeoff is easy to see.

Notice that none of these rows say one method is “better.” A weekend prototype does not want team scalability. A payments system does not want speed at the cost of correctness. The right column depends entirely on what you are building.

Stop asking “which method is better?” Start asking “which method is better for this task?” Here is how I decide.

The case for spec-driven development is not philosophical. It shows up in the data on what unstructured, AI-accelerated coding does to a codebase over time.

GitClear's 2025 AI Copilot Code Quality report, which analyzed roughly 211 million changed lines of code from 2020 to 2024, found that the share of “moved” (refactored) lines fell from 24.1% in 2020 to 9.5% in 2024, while copy/pasted lines climbed from 8.3% to 12.3%, a relative increase of about 48%. Blocks of five or more duplicated lines rose roughly eightfold in 2024, and that year was the first time copy/pasted lines outnumbered refactored ones. In other words: AI makes it cheap to add code and rare to consolidate it. That is the exact opposite of what a healthy, long-lived codebase needs.

And speed itself is not guaranteed. A METR randomized controlled trial found that experienced open-source developers took 19% longer to complete tasks with early-2025 AI tools, even though they believed the tools had made them about 20% faster. Unstructured AI assistance can feel fast while quietly costing you time and quality. A spec is how you claim the speed without paying that tax.

This is also why the human review layer matters more than ever. When agents write most of the code, the spec is what gives a reviewer something concrete to check the output against.

The honest answer is that good teams use both, in sequence. You vibe to explore and spec to ship. The Towards Data Science framing captures it well: vibe coding is how you discover what to build; spec-driven development is how you harden it into something that lasts.

My own loop looks like this. When I am chasing an idea, I vibe: fast, messy, throwaway. The moment that idea earns a place in the real codebase, I stop, write the spec, and let the agent build against it. The prototype gets thrown away, not promoted. That single discipline, refusing to let a vibe become a foundation, is most of the value.

This mirrors the role-based development model we have written about: you are the architect and reviewer, the agents are the implementers, and the spec is the contract between you. It also pairs naturally with the skills and plugins that make agents reliable enough to delegate real work to.

There is a reason spec-driven development clicks for us at TurboDocx. The entire premise of our platform is that a structured document should be the source of truth from which finished output is generated. A template and its variables drive a polished proposal, SOW, or contract, the same way a spec drives a feature.

If you are building tooling around that idea, turning structured input into reliable, repeatable output, our document automation API and SDK are designed exactly for spec-driven workflows. You describe what the document should contain, and the system produces it. No vibes required.