---
title: "Discussion on \"Agentic Harness: What Spec Driven Development Actually Is\" | Hashnode"
description: "Discussion on \"Agentic Harness: What Spec Driven Development Actually Is\". What spec-driven development is, where it came from, and how Spec Kit, Kiro, OpenSpec, BMAD and Tessl compare for AI coding agents."
url: "https://hashnode.com/posts/agentic-harness-what-spec-driven-development-actually-is/6adbdbe49d064b5ab1b4e7a3"
---

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# [Agentic Harness: What Spec Driven Development Actually Is](https://juliantellez.hashnode.dev/agentic-harness-what-spec-driven-development-actually-is?utm_source=hashnode&utm_medium=feed)

What spec-driven development is, where it came from, and how Spec Kit, Kiro, OpenSpec, BMAD and Tessl compare for AI coding agents.

Oct 23 · 13 min read · juliantellez.hashnode.dev  
Updated 4d ago  
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## Written by

[Julian Tellez](https://hashnode.com/@julian-tellez)

@julian-tellez · London, UK

  
[View profile](https://hashnode.com/@julian-tellez)

Senior engineer building with AI agents. Ex Sky, ITV, DAZN, Peacock.

I'm Julian, a software engineer with 15 years' experience, 10 of them building video streaming platforms for Sky, ITV, DAZN and Peacock. These days AI agents write most of my code and I do the architecture. I write about spec-driven development, agentic harnesses, and taking AI-built apps from demo to production. Free community: https://www.skool.com/vibe-coding-to-production-3790

## Responses 1

Markdown supported · ⌘↵ to post

[Dmitry Yurkin](https://hashnode.com/@dmitry-yurkin)

[Oct 26](https://hashnode.com/posts/agentic-harness-what-spec-driven-development-actually-is/6adbdbe49d064b5ab1b4e7a3/comment/6adf5de968afba8fc152cf41)

In our experience, living specs work better as a versioned source of truth for how the product should behave. A change proposal describes the delta, while the living specs describe the resulting system. Revision history makes changes easier to manage and helps the agent understand exactly what changed.

Verifying against incremental specs alone is harder because they leave the behavior that should remain unchanged to be reconstructed. With a maintained current specification, we can verify the affected code against that source of truth after each change. That's the approach we've built into Reqode.