# Build key interface parts once

A key interface part is a part that more than one view shows: main navigation, the header, status words, attention colours, a control that appears in many places.

What it can see: only this page.

[Source on GitHub](https://github.com/mbsi-labs/skills/tree/main/rules/shared-interface-parts).

## The rule itself

A key interface part is a part that more than one view shows: main navigation, the header, status words, attention colours, a control that appears in many places. Build each key part once, as one component, and use that component in every view.

When a new view needs a key part that already exists, use the component. Do not copy it, and do not draw a part that only looks the same.

A part that belongs to one page goes beside or under the shared part. It never replaces the shared part.

A mock or prototype starts from the product's shared parts. It does not draw its own header or navigation.

A change to a key part changes every view at once. Before you call the change complete, look at each view that uses the part.

## Use it

Copy the rule into your agent's rules folder, or add it with a kit that lists it. Your agent reads it at the start of each session.

## Used by

- [images](/kits/images) (kit)
- [product](/kits/product) (kit)

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Published 2026-10-29. Web page: https://www.mackenziebowes.com/rules/shared-interface-parts Part of [Rules](https://www.mackenziebowes.com/rules).