Why should project documents act as the source of truth for an AI coding agent?

Why should project documents act as the source of truth for an AI coding agent?

Project documents give an AI coding agent a durable definition of what the application should do. A conversation may mention a feature once, while an approved PRD, architecture note, and API contract make the same decision available during implementation, review, and later maintenance.

Connect each document to a decision

For a wedding application, the PRD might say that organizers can edit event details and guests can only view published events. The architecture explains where those permissions are enforced. The database design describes event ownership, and the API document defines the edit request.

These documents answer different questions. Together, they help the agent connect a screen to real behavior instead of inventing missing requirements from a visual mockup. The design reference guides appearance; it should not silently expand permissions or introduce unsupported features.

Resolve disagreements before implementation

Suppose a dashboard design shows a public guest list, but the approved requirements make guest details private. Ask the agent to identify the conflict and explain the affected components before changing code. The product owner can clarify the intended behavior, and the documents can then be updated together.

A useful task instruction is: “Implement event editing against the approved requirements, identify conflicting references, and describe any assumptions that affect access or stored data.”

Keep the source of truth current

Documents are useful because they record agreed decisions, not because every sentence remains correct forever. When the team changes a requirement, update its acceptance criteria and related contracts in the same increment.

During review, trace the completed behavior back to those criteria. Verify the actual code and tests as well: documentation describes intent, while implementation evidence shows whether that intent was achieved.