I Used GitHub's Spec Kit for 30 Days. Here's the Truth.

GitHub's Speckit is a specification-driven development toolkit designed to address the core problems of vibe coding: lack of deliberate decision-making, missing tradeoff analysis, and poor documentation. The workflow follows spec → plan → tasks → implementation, forcing developers to answer 'why' and 'what' before 'how'. After 30 days of real-world use, the key benefits include tool-agnostic design (works with Copilot, Cursor, Claude Code, Gemini), natural documentation generation, brownfield project support via a 'constitution' file, and baked-in best practices like TDD and contract testing. Main drawbacks include being too opinionated for established teams, a slow feedback cycle that feels waterfall-like, and heavy context window consumption that can cause compaction issues and token burn. The sweet spot is non-developer technical users building prototypes, or developers exploring unfamiliar domains. For experienced developers on well-understood projects, it adds friction without proportional value.