Web standards

Components

• One job per component. If the name needs "and", split it.
• Props in, events out. A component does not reach into global state it was not given.
• Server-render by default; reach for a client component only when you need interactivity.

State

• URL for anything shareable or reloadable.
• No duplicated source of truth. Derive, do not copy.
• An uncontrolled input that reflects server data needs a key tied to that data, or it will show a stale value after a save.

Accessibility (non-negotiable)

• Every interactive element is reachable and operable by keyboard.
• Every input has a label — visually hidden is fine, absent is not.
• Focus is visible. Do not remove the outline without replacing it.
• Colour is never the only carrier of meaning.
• Text contrast is at least 4.5:1.

Performance

• Measure before optimising.
• Images are sized and lazy below the fold.
• Watch the bundle. A date library is rarely worth 70 KB.

Review checklist

• Works with the keyboard alone
• Inputs are labelled
• Loading and error states exist, not just the happy path
• No layout shift once data arrives
• Nothing secret in client-side code