The Spec-First Development Showdown: Spec Kit, OpenSpec, BMad and Gangsta Agents Compared

GitHub Spec Kit, OpenSpec, BMad Method, and Gangsta Agents all implement spec-first development but with different philosophies. Here’s how they actually differ - and how to choose.

Ask Claude or Copilot to “add user authentication” and you’ll get something. Whether that something matches what you actually need depends on twenty silent inferences the agent made: which auth pattern, which session strategy, which security level, which error handling. None of them written down. None of them reviewable. All of them yours to debug later.

This is the structural failure SDD addresses. But “spec-first” is one principle implemented four very different ways. GitHub Spec Kit, OpenSpec, BMad Method, and Gangsta Agents agree that the spec comes before the code — they disagree on almost everything else: how strict the gates are, where the spec lives, whether agents debate, whether memory persists across sessions.

I’ll compare them across five axes that actually...

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