Why should planning documents be completed before coding begins?

Why should planning documents be completed before coding begins?

Planning documents give developers and AI assistants a shared baseline for what to build and how the main pieces should fit together. Preparing that baseline before feature coding reduces the risk of producing attractive screens backed by incompatible assumptions.

Resolve decisions that affect several features

A PRD defines the users, journeys, and scope. Architecture identifies component responsibilities. Database design explains stored information and relationships. API design describes the operations that connect the interface to server behavior.

In a wedding-management application, deciding whether guests respond per event affects the guest journey, invitation records, API payloads, and dashboard design. If each part invents its own answer during coding, the resulting work may require substantial rework.

Write enough to guide the next increment

Useful planning does not require predicting every future feature. Document the current release, important constraints, acceptance criteria, and unresolved questions. Make assumptions visible so implementation work can test them.

For example, the first increment might only let an organizer create an event and view it in the dashboard. The documents should define that flow, its required data, and its access checks before asking an AI assistant to implement it.

Keep documentation connected to learning

Prototypes and user feedback can reveal problems in an initial plan. When they do, update the relevant documents and explain the decision instead of treating the original draft as permanent.

Ask AI to compare the documents for contradictory names, missing states, or inconsistent permissions before coding begins. Then use the reviewed files as context for each implementation task. Planning is most useful when it provides clear direction while remaining easy to revise as the team learns more about the product.