Metadata

A page or layout can export a static metadata object, or an async generateMetadata() for values that depend on route params:

import type { Metadata } from 'murasaki'

export const metadata: Metadata = {
  title: 'Blog',
  description: 'Posts about murasaki.',
}

import type { GenerateMetadata } from 'murasaki'

export const generateMetadata: GenerateMetadata = async ({ params }) => {
  return { title: `Post: ${params.slug}` }
}

generateMetadata receives { params } — the same dynamic-segment params useParams() reads on the client — so it can fetch a title from a CMS, an API route, or anything else async.

The Metadata shape

interface Metadata {
  title?: string
  description?: string
  icons?: {
    icon?: string
    shortcut?: string
    apple?: string
  }
  openGraph?: {
    title?: string
    description?: string
    images?: string[]
  }
}

Layouts set defaults, pages override them

A layout's metadata (or its page's) merges root → leaf: each ancestor layout's fields apply first, then the matched page's on top — so a layout can set a fallback description or openGraph.images that every page under it inherits unless it sets its own:

export const metadata: Metadata = {
  title: 'My App',
  openGraph: { images: ['/og-default.png'] },
}

export const metadata: Metadata = {
  title: 'My Post',
  // openGraph.images still resolves to '/og-default.png' from the layout —
  // only fields a page actually sets override the ones above it.
}

The merge is per-field, not whole-object: icons and openGraph are merged key by key (a page setting openGraph.title doesn't drop the layout's openGraph.images), while top-level fields like title simply overwrite.

A page's generateMetadata (if present) is awaited and merged on top of that whole static chain last — so it can override any field the static exports set, including a layout's.

How it's applied

On every navigation, <AppRouter> resolves this whole chain and applies it to the document:

• document.title (only touched when a title actually resolves — never blanked out)
• <meta name="description">
• Open Graph <meta property="og:..."> tags (falling back to title / description when openGraph fields are omitted)
• <link rel="icon">, from icons.icon

Tags Murasaki previously added are removed before the new ones are applied, so navigating between routes replaces them cleanly instead of accumulating stale tags from the last route. applyMetadata (the function doing this, exported if you ever need to call it yourself) is a no-op outside a DOM environment.

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