AI coding tools can build quickly, but they can also build the wrong thing quickly. Starting implementation from a vague feature request leaves important decisions about scope, architecture, edge cases, success criteria, and expected behavior to be made implicitly during coding. I created a spec-generator agent that sits between an idea and implementation. I give it a feature request, product vision, or rough description of what I want to build. It investigates the existing project, identifies missing decisions and constraints, researches external dependencies when necessary, and turns the request into a detailed specification that another AI agent can implement without having to guess what I meant. The finished specification becomes the source of truth for the rest of the development workflow. Step-by-step: 1. I give the spec-generator the feature or product idea I want to build, along with any existing requirements, vision documents, or constraints. 2. I have it inspect the existing project before proposing a solution. It needs to understand the current architecture, conventions, capabilities, and relevant prior decisions rather than designing the feature in isolation. 3. I have it identify ambiguities and missing decisions, including questions about users, behavior, scope, dependencies, edge cases, data requirements, integrations, and what is explicitly out of scope. 4. I have it research external technologies, APIs, libraries, or platform capabilities when the design depends on facts that cannot be determined from the repository alone. 5. I have it translate the idea into a layered specification: first the product purpose and desired outcomes, then the technical architecture, and finally the detailed implementation requirements. 6. I have it define measurable success criteria and acceptance tests so that “done” means something concrete rather than simply “the code was written.” 7. I have it persist the finished specification in the project so developers or coding agents can treat it as the source of truth during implementation. 8. I pass the specification through a separate review or validation step before coding begins, resolving gaps or contradictions in the spec rather than discovering them halfway through implementation. Instead of asking an AI coding agent to interpret a rough idea while it writes code, I separate figuring out what should be built from building it.