Understanding Spec-Driven-Development: Kiro, Spec-Kit, and Tessl

Summary

I’ve been trying to understand one of the latest AI coding buzzword: Spec-driven development (SDD). I looked at three of the tools that label themselves as SDD tools and tried to untangle what it means, as of now. Definition Like with many emerging terms in this fast-paced space, the definition of “spec-driven development” (SDD) is still in flux. Here’s what I can gather from how I have seen it used so far: Spec-driven development means writing a “spec” before writing code with AI (“documentation first”). The spec becomes the source of truth for the human and the AI. GitHub: “In this new world, maintaining software means evolving specifications. […] The lingua franca of development moves to a higher level, and code is the last-mile approach.” Tessl: “A development approach where specs — not code — are the primary artifact. Specs describe intent in structured, testable language, and agents generate code to match them.” After looking over the usages of the term, and some of the tools that claim to be implementing SDD, it seems to me that in reality, there are multiple implementation levels to it: Spec-first: A well thought-out spec is written first, and then used in the AI-assisted development workflow for the task at hand. Spec-anchored: The spec is kept even after the task is complete, to continue using it for evolution and maintenance of the respective feature. Spec-as-source: The spec is the main source file over time, and only the spec is edited by the human, the human never touches the code. All SDD approaches and definitions I’ve found are spec-first, but not all strive to be spec-anchored or spec-as-source. And often it’s left vague or totally open what the spec maintenance strategy over time is meant to be. What is a spec? The key question in terms of definitions of course is: What is a spec? There doesn’t seem to be a general definition, the closest I’ve seen to a consistent definition is the comparison of a spec to a “Product Requirements Document”. The ter...