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When the Tool Is Its Own Proof

Building an open-source Claude skill that implements the Specification Engineering framework — and discovering the SKILL.md is itself a spec.

3 min readDecember 2025

Outcome

Designed and shipped 'specify' — an open-source Claude skill that walks any agent task through the Five Pillars of Specification Engineering — and published it as a reusable workflow anyone can deploy.

From Framework to Tool

Developing the Specification Engineering framework answered the why: vague AI instructions aren't a style problem, they're a thinking problem, and the discipline of writing a real spec forces you to resolve your own ambiguity before asking an agent to work.

But a framework sitting in a Medium article doesn't change how anyone actually builds. The question was how to encode it as something repeatable — a workflow someone could run every time they needed to spec out an agent task, without having to remember the Five Pillars from scratch.

The answer was a Claude skill.

What a Skill Is

A Claude skill is a reusable, structured workflow stored as a SKILL.md file. When invoked, it gives Claude a specific set of instructions, conversation patterns, and output formats to follow — turning a free-form AI session into a guided, predictable process.

The specify skill walks through the Five Pillars of Specification Engineering as a structured conversation. It gathers the information needed for each pillar, drafts the spec content for that section, reviews it with you before moving on, and produces a complete .md specification file at the end — ready for any executor, human or agent, to use as a standalone brief.

The Recursive Proof

Here's what I didn't fully anticipate until I was building it: the specify SKILL.md is itself a complete specification for how specification conversations should go.

Every step in the workflow is an acceptance criterion applied to the spec-writing process. The constraint architecture defines what the skill must do, what it can never do, and when it should escalate for clarification. The decomposition breaks the five-pillar conversation into independently executable steps. The evaluation design describes what a complete, usable specification looks like.

The thing is its own proof of concept.

This wasn't a clever design decision — it emerged from taking the framework seriously during implementation. When you build something using its own methodology, you find out immediately whether the methodology actually works. In this case, it did.

Open Source by Design

The specify skill is fully open source on GitHub: github.com/scanton/specify

The decision to open source it was straightforward. The value of Specification Engineering isn't in the tool — it's in the discipline of thinking clearly before delegating. Publishing the skill openly puts the workflow in front of anyone building with agents, and makes the framework concrete rather than theoretical.

If someone forks it, adapts it, or improves on it, that's the point.

What This Demonstrates

The Specification Engineering framework is a consulting offering. The specify skill is evidence that the framework is real, not aspirational.

Any consultant can describe a methodology. Fewer can show you a working implementation of it. The specify skill is the difference between saying "you should write better specs" and shipping a tool that walks you through exactly how to do it.

That gap — between describing an approach and building a tool that embodies it — is where most AI strategy work stays. Crossing it is the part I find interesting.


The full write-up on the framework is on Medium: The Spec Is the System

The skill is available to clone and use: github.com/scanton/specify

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