What is a PRD (Product Requirements Document)?
TL;DR: A Product Requirements Document (PRD) outlines the business goals, user stories, and features of a product. It tells you what to build. In traditional software development, humans translate the PRD into an architecture. In AI development, feeding a PRD directly to a coding agent forces the AI to guess the architecture—usually leading straight to the doom loop.
The Traditional Definition
A Product Requirements Document (PRD) is the business blueprint for a feature or application. Historically written by Product Managers, it serves as the single source of truth for what needs to be built.
A standard PRD includes:
- Problem Statement: Why are we building this?
- Target Audience: Who is this for?
- User Stories: "As a user, I want to [action] so that [benefit]."
- Acceptance Criteria: How do we know the feature is done and working?
- Out of Scope: What are we deliberately not building?
In a traditional dev team, the PM hands this document to a senior engineer. That engineer reads it, thinks about the existing codebase, designs a database schema, and figures out how to build it.
Why PRDs Break AI Agents
Tools like Windsurf, Cursor, and Bolt are incredible executors, but they are not senior architects.
If you paste a standard PRD into an AI agent and tell it to start coding, the agent understands the features but lacks the technical boundaries. It will enthusiastically start generating UI components and backend routes. But because the PRD didn't specify a database schema, component hierarchy, or state management strategy, the agent invents them on the fly.
When you ask for changes on day three, the agent forgets its own made-up architecture, hallucinates new dependencies, and breaks existing code. You hit the 80% wall.
PRD vs. ADD (Architecture Design Document)
To successfully build with AI, you have to separate the "What" from the "How."
- The PRD defines the What. (User needs, features, business logic).
- The ADD defines the How. (Database schema, API boundaries, tech stack).
Frequently asked questions (FAQs)
What’s the difference between a PRD and a BRD? A Business Requirements Document (BRD) focuses on business objectives and stakeholder needs. A PRD focuses on product features and user stories. Neither defines technical architecture.
Can I use a PRD with an AI coding agent? You can, but the agent will fill in the missing architecture on its own, picking your schema, your component structure, your API boundaries. For simple prototypes that’s workable. For production builds, it starts to break down.
Does Zalcro replace the PRD? No. Zalcro takes your product requirements as input and outputs the architectural layer, the ADD and Prompt Pack, that sits between the PRD and the coding agent. You still need to know what you’re building.
What should a PRD include for AI development? In addition to the standard elements (user stories, acceptance criteria, out of scope), a PRD for AI development should explicitly define phase boundaries: what’s in v1 and what’s not. The agent shouldn’t know about features it isn’t building yet.
Zalcro takes your PRD as its starting point and generates the Architecture Design Document and Prompt Pack your agent needs to build from.