feat(seo): sitemap, robots, canonical URLs, OG images and JSON-LD

- Add sitemap.ts and robots.ts
- pageMetadata() helper: consistent title, canonical URL, Open Graph,
  Twitter card and feed alternate on every page
- Generated OG images: a site card, and per post either the cover image
  or a branded title card (pre-rendered at build)
- BlogPosting JSON-LD on post pages
- Fail fast with a clear error when SITE_URL is missing

Content loading:
- Validate post frontmatter at build time and normalize dates to ISO
  (fixes invalid <time datetime> values)
- Add draft: true support (drafts only render in development)
- Cache markdown rendering so metadata and page share one render
- Replace the three copy-pasted about/projects/setup pages with a shared
  MarkdownPage component

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/(withRecent)/categories/[categorySlug]/page.tsx

@@ -1,4 +1,4 @@
-import { metadata } from '@/app/metadata'
+import { pageMetadata } from '@/app/metadata'
 import { getAllCategories, getCategoryBySlug, getPostsByCategory } from '@/lib/categories'
 import { dateFormatter } from '@/utils/time'
 import type { Metadata } from 'next'
@@ -26,17 +26,11 @@ export async function generateMetadata({ params }: CategoryPageProps): Promise<M
   const category = getCategoryBySlug(categorySlug)
   if (!category) notFound()
 
-  return {
+  return pageMetadata({
-    title: `${category} | ${metadata.title!.toString()}`,
+    title: category,
-    description: 'List of posts in this category',
+    description: `Posts in the “${category}” category`,
-    openGraph: {
+    path: `/categories/${categorySlug}`,
-      type: 'website',
+  })
-      title: `${category} | ${metadata.title!.toString()}`,
-      description: 'List of posts in this category',
-      url: process.env.SITE_URL + `/categories/${categorySlug}`,
-      siteName: metadata.title!.toString(),
-    },
-  }
 }
 
 export default async function CategoryPage({ params }: CategoryPageProps) {

app/(withRecent)/categories/page.tsx

@@ -3,21 +3,15 @@ import { getAllPostsMeta } from '@/lib/posts'
 import { slugify } from '@/utils/slug'
 import type { Metadata } from 'next'
 import Link from 'next/link'
-import { metadata } from '@/app/metadata'
+import { pageMetadata } from '@/app/metadata'
 import { dateFormatter } from '@/utils/time'
 
 export async function generateMetadata(): Promise<Metadata> {
-  return {
+  return pageMetadata({
-    title: `Categories | ${metadata.title!.toString()}`,
+    title: 'Categories',
-    description: 'List of categories',
+    description: 'All post categories on the blog',
-    openGraph: {
+    path: '/categories',
-      type: 'website',
+  })
-      title: `Categories | ${metadata.title!.toString()}`,
-      description: 'List of categories',
-      url: process.env.SITE_URL + '/categories',
-      siteName: metadata.title!.toString(),
-    },
-  }
 }
 
 export default function CategoriesPage() {

app/(withRecent)/page.tsx

@@ -1,5 +1,8 @@
 import { getAllPostsMeta } from '@/lib/posts'
 import { Post } from '@/components/post/Post'
+import type { Metadata } from 'next'
+
+export const metadata: Metadata = { alternates: { canonical: '/' } }
 
 export default function Homepage() {
   const posts = getAllPostsMeta()

app/(withRecent)/tags/[tagSlug]/page.tsx

@@ -1,4 +1,4 @@
-import { metadata } from '@/app/metadata'
+import { pageMetadata } from '@/app/metadata'
 import { getAllTags, getPostsByTag, getTagBySlug } from '@/lib/tags'
 import { dateFormatter } from '@/utils/time'
 import type { Metadata } from 'next'
@@ -26,17 +26,11 @@ export async function generateMetadata({ params }: TagPageProps): Promise<Metada
   const tag = getTagBySlug(tagSlug)
   if (!tag) notFound()
 
-  return {
+  return pageMetadata({
-    title: `${tag} | ${metadata.title!.toString()}`,
+    title: tag,
-    description: 'List of posts in this tag',
+    description: `Posts tagged “${tag}”`,
-    openGraph: {
+    path: `/tags/${tagSlug}`,
-      type: 'website',
+  })
-      title: `${tag} | ${metadata.title!.toString()}`,
-      description: 'List of posts in this tag',
-      url: process.env.SITE_URL + `/tags/${tagSlug}`,
-      siteName: metadata.title!.toString(),
-    },
-  }
 }
 
 export default async function TagPage({ params }: TagPageProps) {

app/(withRecent)/tags/page.tsx

@@ -3,21 +3,11 @@ import { getAllPostsMeta } from '@/lib/posts'
 import { slugify } from '@/utils/slug'
 import type { Metadata } from 'next'
 import Link from 'next/link'
-import { metadata } from '@/app/metadata'
+import { pageMetadata } from '@/app/metadata'
 import { dateFormatter } from '@/utils/time'
 
 export async function generateMetadata(): Promise<Metadata> {
-  return {
+  return pageMetadata({ title: 'Tags', description: 'All tags used on the blog', path: '/tags' })
-    title: `Tags | ${metadata.title!.toString()}`,
-    description: 'List of tags',
-    openGraph: {
-      type: 'website',
-      title: `Tags | ${metadata.title!.toString()}`,
-      description: 'List of tags',
-      url: process.env.SITE_URL + '/tags',
-      siteName: metadata.title!.toString(),
-    },
-  }
 }
 
 export default function TagsPage() {

app/about/page.tsx

@@ -1,35 +1,7 @@
-import { metadata } from '@/app/metadata'
+import { MarkdownPage, markdownPageMetadata } from '@/components/content/MarkdownPage'
-import { TableOfContents } from '@/components/post/TableOfContents'
-import { getPostBySlug } from '@/lib/posts'
-import type { Metadata } from 'next'
 
-export async function generateMetadata(): Promise<Metadata> {
+export const generateMetadata = () => markdownPageMetadata('about')
-  const { meta } = await getPostBySlug('about', 'content/pages')
+
-  return {
+export default function AboutPage() {
-    title: `${meta.title} | ${metadata.title!.toString()}`,
+  return <MarkdownPage slug="about" />
-    description: meta.description,
-    openGraph: {
-      type: 'website',
-      title: `${meta.title} | ${metadata.title!.toString()}`,
-      description: meta.description,
-      url: process.env.SITE_URL + `/about`,
-      siteName: metadata.title!.toString(),
-    },
-  }
-}
-
-export default async function AboutPage() {
-  const { meta, content, tableOfContents } = await getPostBySlug('about', 'content/pages')
-
-  return (
-    <main className="flex w-full">
-      <article className="max-w-3xl 2xl:max-w-4xl mx-auto px-4 py-8 mb-8 lg:py-16 min-w-0">
-        <h1 className="text-4xl font-bold mb-4">{meta.title}</h1>
-        <p className="text-fg text-lg mb-4">{meta.description}</p>
-        <div className="prose">{content}</div>
-      </article>
-
-      <TableOfContents items={tableOfContents} />
-    </main>
-  )
 }

app/feed.xml/route.ts

@@ -1,11 +1,9 @@
-import { metadata } from '@/app/metadata'
+import { AUTHOR, SITE_NAME, SITE_URL } from '@/app/metadata'
 import { getAllPostsMeta } from '@/lib/posts'
 import type { PostMeta } from '@/types/Post.type'
 
 export const dynamic = 'force-static'
 
-const SITE_URL = process.env.SITE_URL
-
 const lastModified = (p: PostMeta) => new Date(p.updated ?? p.date)
 
 function escapeXml(str: string) {
@@ -46,14 +44,15 @@ export async function GET(req: Request) {
   const feed = `<?xml version="1.0" encoding="UTF-8"?>
 <feed xmlns="http://www.w3.org/2005/Atom">
   <id>${SITE_URL}/</id>
-  <title>${escapeXml(metadata.title!.toString())}</title>
+  <title>${escapeXml(SITE_NAME)}</title>
   <updated>${updated}</updated>
   <author>
-    <name>${escapeXml(metadata.creator!.toString())}</name>
+    <name>${escapeXml(AUTHOR.name)}
+    <uri>${AUTHOR.url}</uri></name>
   </author>
   <link href="${SITE_URL}/feed.xml" rel="self" type="application/atom+xml" />
   <link href="${SITE_URL}" rel="alternate" type="text/html" />
-  <rights> © ${new Date().getFullYear()} Frank Borisjuk </rights>
+  <rights>© ${new Date().getFullYear()} ${escapeXml(AUTHOR.name)}</rights>
   ${entries}
 </feed>`
 

app/metadata.ts

@@ -1,20 +1,84 @@
 import { Metadata } from 'next'
 
+if (!process.env.SITE_URL) {
+  throw new Error('SITE_URL environment variable is not set (e.g. SITE_URL=https://example.com)')
+}
+
+export const SITE_URL = process.env.SITE_URL.replace(/\/$/, '')
+export const SITE_NAME = 'Ephemeris'
+export const SITE_DESCRIPTION = 'A blog about me and my interests'
+export const AUTHOR = { name: 'Frank Borisjuk', handle: 'hangerthem', url: SITE_URL + '/about' }
+
+// Child segments replace `alternates` wholesale, so every page re-declares the feed link
+const feedAlternate = { 'application/atom+xml': [{ url: '/feed.xml', title: SITE_NAME }] }
+
 export const metadata: Metadata = {
-  metadataBase: new URL(process.env.SITE_URL!),
+  metadataBase: new URL(SITE_URL),
-  title: 'Ephemeris',
+  title: SITE_NAME,
-  description: 'A blog about me and my interests',
+  description: SITE_DESCRIPTION,
-  creator: 'hangerthem',
+  creator: AUTHOR.handle,
+  authors: [{ name: AUTHOR.name, url: AUTHOR.url }],
+  alternates: { types: feedAlternate },
   openGraph: {
     type: 'website',
-    title: 'Ephemeris',
+    title: SITE_NAME,
-    description: 'A blog about me and my interests',
+    description: SITE_DESCRIPTION,
-    url: process.env.SITE_URL,
+    url: SITE_URL,
-    siteName: 'Ephemeris',
+    siteName: SITE_NAME,
+  },
+  twitter: {
+    card: 'summary_large_image',
+    title: SITE_NAME,
+    description: SITE_DESCRIPTION,
   },
   appleWebApp: {
-    title: 'Ephemeris',
+    title: SITE_NAME,
     statusBarStyle: 'default',
     capable: true,
   },
 }
+
+type PageMetadataOptions = {
+  title: string
+  description: string
+  /** Path relative to the site root, starting with a slash. */
+  path: string
+  /** Open Graph / Twitter image URL. Defaults to the generated site card. */
+  image?: string
+  openGraph?: Metadata['openGraph']
+}
+
+// Generated by app/opengraph-image.tsx. Child segments that set `openGraph` don't inherit
+// file-based images, and explicit images win over them, so every page names its image here.
+const defaultOgImage = '/opengraph-image'
+
+/** Builds consistent page metadata (title, canonical URL, Open Graph and Twitter card). */
+export function pageMetadata({
+  title,
+  description,
+  path,
+  image = defaultOgImage,
+  openGraph,
+}: PageMetadataOptions): Metadata {
+  const fullTitle = `${title} | ${SITE_NAME}`
+  return {
+    title: fullTitle,
+    description,
+    alternates: { canonical: path, types: feedAlternate },
+    openGraph: {
+      type: 'website',
+      title: fullTitle,
+      description,
+      url: SITE_URL + path,
+      siteName: SITE_NAME,
+      images: image,
+      ...openGraph,
+    },
+    twitter: {
+      card: 'summary_large_image',
+      title: fullTitle,
+      description,
+      images: image,
+    },
+  }
+}

app/opengraph-image.tsx

@@ -0,0 +1,10 @@
+import { SITE_DESCRIPTION, SITE_NAME } from '@/app/metadata'
+import { ogImageSize, renderOgCard } from '@/lib/og-image'
+
+export const alt = SITE_NAME
+export const size = ogImageSize
+export const contentType = 'image/png'
+
+export default function OpengraphImage() {
+  return renderOgCard({ title: SITE_NAME, description: SITE_DESCRIPTION })
+}

app/posts/[slug]/opengraph-image.tsx

@@ -0,0 +1,19 @@
+import { getAllPostSlugs, getPostMeta } from '@/lib/posts'
+import { ogImageSize, renderOgCard, renderOgCover } from '@/lib/og-image'
+
+export const size = ogImageSize
+export const contentType = 'image/png'
+
+export function generateStaticParams() {
+  return getAllPostSlugs().map((slug) => ({ slug }))
+}
+
+/** Uses the post's cover image when it has one, otherwise a generated title card. */
+export default async function OpengraphImage({ params }: { params: Promise<{ slug: string }> }) {
+  const { slug } = await params
+  const meta = getPostMeta(slug)
+  return (
+    (meta.coverImage && renderOgCover(meta.coverImage)) ??
+    renderOgCard({ title: meta.title, description: meta.description, eyebrow: meta.category })
+  )
+}

app/posts/[slug]/page.tsx

@@ -1,4 +1,4 @@
-import { metadata } from '@/app/metadata'
+import { AUTHOR, pageMetadata, SITE_NAME, SITE_URL } from '@/app/metadata'
 import { ImageWrapper } from '@/components/content/ImageWrapper'
 import { ShareLinks } from '@/components/post/ShareLinks'
 import { TableOfContents } from '@/components/post/TableOfContents'
@@ -21,29 +21,52 @@ export async function generateMetadata({
 }): Promise<Metadata> {
   const { slug } = await params
   const { meta } = await getPostBySlug(slug)
-  return {
+  return pageMetadata({
-    title: `${meta.title} | ${metadata.title!.toString()}`,
+    title: meta.title,
     description: meta.description,
+    path: `/posts/${slug}`,
+    image: `/posts/${slug}/opengraph-image`,
     openGraph: {
       type: 'article',
-      title: `${meta.title} | ${metadata.title!.toString()}`,
+      publishedTime: meta.date,
-      description: meta.description,
+      modifiedTime: meta.updated,
-      url: process.env.SITE_URL + `/posts/${slug}`,
+      authors: [AUTHOR.url],
-      images: meta.coverImage ? [`/posts/${meta.coverImage}`] : undefined,
+      section: meta.category,
       tags: meta.tags,
-      ...(meta.updated && { modifiedTime: new Date(meta.updated).toISOString() }),
-      siteName: metadata.title!.toString(),
     },
-  }
+  })
 }
 
 export default async function Post({ params }: { params: Promise<{ slug: string }> }) {
   const { slug } = await params
   const { meta, content, tableOfContents } = await getPostBySlug(slug)
   const { next, previous } = getNextAndPreviousPosts(slug)
+  const url = `${SITE_URL}/posts/${slug}`
+
+  const jsonLd = {
+    '@context': 'https://schema.org',
+    '@type': 'BlogPosting',
+    headline: meta.title,
+    description: meta.description,
+    url,
+    mainEntityOfPage: url,
+    datePublished: meta.date,
+    dateModified: meta.updated ?? meta.date,
+    image: `${url}/opengraph-image`,
+    articleSection: meta.category,
+    keywords: meta.tags.join(', '),
+    author: { '@type': 'Person', name: AUTHOR.name, url: AUTHOR.url },
+    publisher: { '@type': 'Person', name: AUTHOR.name, url: AUTHOR.url },
+    isPartOf: { '@type': 'Blog', name: SITE_NAME, url: SITE_URL },
+  }
 
   return (
     <main className="flex w-full">
+      <script
+        type="application/ld+json"
+        // Escape "<" so post content can never close the script tag early
+        dangerouslySetInnerHTML={{ __html: JSON.stringify(jsonLd).replace(/</g, '\\u003c') }}
+      />
       <article className="max-w-3xl 2xl:max-w-4xl mx-auto px-4 py-8 mb-8 lg:py-16 min-w-0">
         {meta.category && (
           <Link
@@ -114,7 +137,7 @@ export default async function Post({ params }: { params: Promise<{ slug: string
         )}
         <div className="prose">{content}</div>
 
-        {meta.tags && (
+        {meta.tags.length > 0 && (
           <div className="mt-6 border-t border-border pt-4 flex gap-2 items-center flex-wrap">
             <h2 className="text-lg font-bold">Tags</h2>
             <div className="flex flex-wrap gap-1">
@@ -132,11 +155,7 @@ export default async function Post({ params }: { params: Promise<{ slug: string
         )}
 
         <div className="mt-8 mx-auto flex">
-          <ShareLinks
+          <ShareLinks url={url} title={meta.title} description={meta.description} />
-            url={process.env.SITE_URL + `/posts/${slug}`}
-            title={meta.title}
-            description={meta.description}
-          />
         </div>
 
         <div className="mt-12 grid grid-cols-1 sm:grid-cols-2 gap-3 sm:gap-4 border-t border-border pt-8">

app/projects/page.tsx

@@ -1,35 +1,7 @@
-import { metadata } from '@/app/metadata'
+import { MarkdownPage, markdownPageMetadata } from '@/components/content/MarkdownPage'
-import { TableOfContents } from '@/components/post/TableOfContents'
-import { getPostBySlug } from '@/lib/posts'
-import type { Metadata } from 'next'
 
-export async function generateMetadata(): Promise<Metadata> {
+export const generateMetadata = () => markdownPageMetadata('projects')
-  const { meta } = await getPostBySlug('projects', 'content/pages')
+
-  return {
+export default function ProjectsPage() {
-    title: `${meta.title} | ${metadata.title!.toString()}`,
+  return <MarkdownPage slug="projects" />
-    description: meta.description,
-    openGraph: {
-      type: 'website',
-      title: `${meta.title} | ${metadata.title!.toString()}`,
-      description: meta.description,
-      url: process.env.SITE_URL + `/projects`,
-      siteName: metadata.title!.toString(),
-    },
-  }
-}
-
-export default async function ProjectsPage() {
-  const { meta, content, tableOfContents } = await getPostBySlug('projects', 'content/pages')
-
-  return (
-    <main className="flex w-full">
-      <article className="max-w-3xl 2xl:max-w-4xl mx-auto px-4 py-8 mb-8 lg:py-16 min-w-0">
-        <h1 className="text-4xl font-bold mb-4">{meta.title}</h1>
-        <p className="text-fg text-lg mb-4">{meta.description}</p>
-        <div className="prose">{content}</div>
-      </article>
-
-      <TableOfContents items={tableOfContents} />
-    </main>
-  )
 }

app/robots.ts

@@ -0,0 +1,9 @@
+import type { MetadataRoute } from 'next'
+import { SITE_URL } from '@/app/metadata'
+
+export default function robots(): MetadataRoute.Robots {
+  return {
+    rules: { userAgent: '*', allow: '/' },
+    sitemap: `${SITE_URL}/sitemap.xml`,
+  }
+}

app/setup/page.tsx

@@ -1,35 +1,7 @@
-import { metadata } from '@/app/metadata'
+import { MarkdownPage, markdownPageMetadata } from '@/components/content/MarkdownPage'
-import { TableOfContents } from '@/components/post/TableOfContents'
-import { getPostBySlug } from '@/lib/posts'
-import type { Metadata } from 'next'
 
-export async function generateMetadata(): Promise<Metadata> {
+export const generateMetadata = () => markdownPageMetadata('setup')
-  const { meta } = await getPostBySlug('setup', 'content/pages')
+
-  return {
+export default function SetupPage() {
-    title: `${meta.title} | ${metadata.title!.toString()}`,
+  return <MarkdownPage slug="setup" />
-    description: meta.description,
-    openGraph: {
-      type: 'website',
-      title: `${meta.title} | ${metadata.title!.toString()}`,
-      description: meta.description,
-      url: process.env.SITE_URL + `/setup`,
-      siteName: metadata.title!.toString(),
-    },
-  }
-}
-
-export default async function SetupPage() {
-  const { meta, content, tableOfContents } = await getPostBySlug('setup', 'content/pages')
-
-  return (
-    <main className="flex w-full">
-      <article className="max-w-3xl 2xl:max-w-4xl mx-auto px-4 py-8 mb-8 lg:py-16 min-w-0">
-        <h1 className="text-4xl font-bold mb-4">{meta.title}</h1>
-        <p className="text-fg text-lg mb-4">{meta.description}</p>
-        <div className="prose">{content}</div>
-      </article>
-
-      <TableOfContents items={tableOfContents} />
-    </main>
-  )
 }

app/sitemap.ts

@@ -0,0 +1,41 @@
+import type { MetadataRoute } from 'next'
+import { SITE_URL } from '@/app/metadata'
+import { getAllCategories } from '@/lib/categories'
+import { getAllPostsMeta } from '@/lib/posts'
+import { getAllTags } from '@/lib/tags'
+import { slugify } from '@/utils/slug'
+
+export default function sitemap(): MetadataRoute.Sitemap {
+  const posts = getAllPostsMeta()
+  const lastPostUpdate = posts
+    .map((post) => post.updated ?? post.date)
+    .toSorted()
+    .at(-1)
+
+  return [
+    { url: SITE_URL, lastModified: lastPostUpdate, changeFrequency: 'weekly', priority: 1 },
+    ...['about', 'projects', 'setup'].map((page) => ({
+      url: `${SITE_URL}/${page}`,
+      changeFrequency: 'monthly' as const,
+      priority: 0.8,
+    })),
+    ...posts.map((post) => ({
+      url: `${SITE_URL}/posts/${post.slug}`,
+      lastModified: post.updated ?? post.date,
+      changeFrequency: 'monthly' as const,
+      priority: 0.9,
+    })),
+    { url: `${SITE_URL}/categories`, changeFrequency: 'weekly', priority: 0.4 },
+    ...Object.keys(getAllCategories()).map((category) => ({
+      url: `${SITE_URL}/categories/${slugify(category)}`,
+      changeFrequency: 'weekly' as const,
+      priority: 0.3,
+    })),
+    { url: `${SITE_URL}/tags`, changeFrequency: 'weekly', priority: 0.4 },
+    ...Object.keys(getAllTags()).map((tag) => ({
+      url: `${SITE_URL}/tags/${slugify(tag)}`,
+      changeFrequency: 'weekly' as const,
+      priority: 0.3,
+    })),
+  ]
+}

components/content/MarkdownPage.tsx

@@ -0,0 +1,27 @@
+import { pageMetadata } from '@/app/metadata'
+import { TableOfContents } from '@/components/post/TableOfContents'
+import { getPageBySlug } from '@/lib/posts'
+import type { Metadata } from 'next'
+
+/** Metadata for a standalone page served at `/<slug>` from content/pages/<slug>.md. */
+export async function markdownPageMetadata(slug: string): Promise<Metadata> {
+  const { meta } = await getPageBySlug(slug)
+  return pageMetadata({ title: meta.title, description: meta.description, path: `/${slug}` })
+}
+
+/** Renders a standalone page from content/pages/<slug>.md. */
+export async function MarkdownPage({ slug }: { slug: string }) {
+  const { meta, content, tableOfContents } = await getPageBySlug(slug)
+
+  return (
+    <main className="flex w-full">
+      <article className="max-w-3xl 2xl:max-w-4xl mx-auto px-4 py-8 mb-8 lg:py-16 min-w-0">
+        <h1 className="text-4xl font-bold mb-4">{meta.title}</h1>
+        <p className="text-fg text-lg mb-4">{meta.description}</p>
+        <div className="prose">{content}</div>
+      </article>
+
+      <TableOfContents items={tableOfContents} />
+    </main>
+  )
+}

components/layout/Sidebar.tsx

@@ -1,4 +1,4 @@
-import { metadata } from '@/app/metadata'
+import { SITE_NAME } from '@/app/metadata'
 import { NavLinks } from '@/components/layout/NavLinks'
 import { siBluesky, siGithub, siMatrix, siTelegram, type SimpleIcon } from 'simple-icons'
 import { ExternalLink } from '@/components/ui/ExternalLink'
@@ -39,7 +39,7 @@ export async function Sidebar() {
         <div>
           <h2 className="text-2xl font-bold mb-4 flex items-center gap-2">
             <Image src="/logo.png" alt="Ephemeris Logo" width={32} height={32} />
-            <span>{metadata.title!.toString()}</span>
+            <span>{SITE_NAME}</span>
           </h2>
           <ul className="space-y-2">
             <NavLinks />

lib/og-image.tsx

@@ -0,0 +1,81 @@
+import fs from 'fs'
+import path from 'path'
+import { ImageResponse } from 'next/og'
+import { SITE_NAME, SITE_URL } from '@/app/metadata'
+
+export const ogImageSize = { width: 1200, height: 630 }
+
+const colors = { bg: '#040404', fg: '#e0e0e0', fgDim: '#b0b0b0', accent: '#ef1f1f' }
+
+function toDataUri(filePath: string, mime: string) {
+  return `data:${mime};base64,${fs.readFileSync(filePath).toString('base64')}`
+}
+
+const logo = toDataUri(path.join(process.cwd(), 'public/logo.png'), 'image/png')
+
+type OgCardProps = {
+  title: string
+  description?: string
+  eyebrow?: string
+}
+
+/** Renders the branded title card used for pages and posts without a cover image. */
+export function renderOgCard({ title, description, eyebrow }: OgCardProps) {
+  return new ImageResponse(
+    <div
+      style={{
+        width: '100%',
+        height: '100%',
+        display: 'flex',
+        flexDirection: 'column',
+        justifyContent: 'space-between',
+        padding: '64px 72px',
+        background: colors.bg,
+        color: colors.fg,
+        borderLeft: `16px solid ${colors.accent}`,
+      }}
+    >
+      <div style={{ display: 'flex', flexDirection: 'column', gap: 20 }}>
+        {eyebrow && (
+          <div style={{ fontSize: 28, color: colors.accent, textTransform: 'uppercase' }}>
+            {eyebrow}
+          </div>
+        )}
+        <div style={{ fontSize: title.length > 50 ? 60 : 76, fontWeight: 700, lineHeight: 1.1 }}>
+          {title}
+        </div>
+        {description && (
+          <div style={{ fontSize: 30, color: colors.fgDim, lineHeight: 1.4, maxHeight: 130 }}>
+            {description.length > 140 ? description.slice(0, 137).trimEnd() + '…' : description}
+          </div>
+        )}
+      </div>
+      <div style={{ display: 'flex', alignItems: 'center', gap: 16, fontSize: 30 }}>
+        {/* oxlint-disable-next-line nextjs/no-img-element -- Satori renders plain <img> only */}
+        <img src={logo} width={48} height={48} alt="" />
+        <span style={{ fontWeight: 700 }}>{SITE_NAME}</span>
+        <span style={{ color: colors.fgDim }}>{SITE_URL.replace(/^https?:\/\//, '')}</span>
+      </div>
+    </div>,
+    ogImageSize,
+  )
+}
+
+const coverMimeTypes: Record<string, string> = {
+  '.png': 'image/png',
+  '.jpg': 'image/jpeg',
+  '.jpeg': 'image/jpeg',
+}
+
+/** Renders a post's cover image at OG size, or null if the format isn't supported by Satori. */
+export function renderOgCover(coverImage: string) {
+  const mime = coverMimeTypes[path.extname(coverImage).toLowerCase()]
+  if (!mime) return null
+
+  const src = toDataUri(path.join(process.cwd(), 'public/posts', coverImage), mime)
+  return new ImageResponse(
+    // oxlint-disable-next-line nextjs/no-img-element -- Satori renders plain <img> only
+    <img src={src} width={ogImageSize.width} height={ogImageSize.height} alt="" />,
+    ogImageSize,
+  )
+}

lib/posts.tsx

@@ -9,7 +9,14 @@ import remarkRehype from 'remark-rehype'
 import rehypeHighlight from 'rehype-highlight'
 import rehypeKatex from 'rehype-katex'
 import rehypeReact from 'rehype-react'
-import { cloneElement, isValidElement, type ReactElement, Fragment, type ReactNode } from 'react'
+import {
+  cache,
+  cloneElement,
+  isValidElement,
+  type ReactElement,
+  Fragment,
+  type ReactNode,
+} from 'react'
 import { jsx, jsxs } from 'react/jsx-runtime'
 import { rehypeCodeMeta } from '@/lib/rehype-code-meta'
 import { CodeWrapper } from '@/components/content/CodeWrapper'
@@ -28,28 +35,86 @@ import { PostMeta } from '@/types/Post.type'
 import Link from 'next/link'
 
 const postsDirectory = path.join(process.cwd(), 'content/posts')
+const pagesDirectory = path.join(process.cwd(), 'content/pages')
 
-export function getAllPostSlugs(): string[] {
+const includeDrafts = process.env.NODE_ENV !== 'production'
-  return fs
+
-    .readdirSync(postsDirectory)
+type TocItem = { text: string; id: string; level: number }
-    .filter((f) => f.endsWith('.md'))
+
-    .map((f) => f.replace(/\.md$/, ''))
+function readMarkdownFile(directory: string, slug: string) {
+  return matter(fs.readFileSync(path.join(directory, `${slug}.md`), 'utf8'))
+}
+
+/**
+ * Validates post frontmatter and normalizes dates to ISO strings.
+ * Throws at build time with the offending file and field instead of rendering a broken post.
+ */
+function parsePostFrontmatter(slug: string, data: Record<string, unknown>) {
+  const fail = (message: string): never => {
+    throw new Error(`Invalid frontmatter in content/posts/${slug}.md: ${message}`)
+  }
+  const requireString = (key: string) => {
+    const value = data[key]
+    return typeof value === 'string' && value.trim() !== ''
+      ? value
+      : fail(`"${key}" is required and must be a non-empty string`)
+  }
+  const optionalString = (key: string) => {
+    const value = data[key]
+    return value === undefined || typeof value === 'string'
+      ? value
+      : fail(`"${key}" must be a string`)
+  }
+  // YAML parses bare dates (2024-08-04) into Date objects, anything with a time stays a string
+  const optionalDate = (key: string) => {
+    const value = data[key]
+    if (value === undefined) return undefined
+    const date = value instanceof Date ? value : new Date(String(value))
+    return Number.isNaN(date.getTime()) ? fail(`"${key}" is not a valid date`) : date.toISOString()
+  }
+
+  const tags = data.tags ?? []
+  if (!Array.isArray(tags) || tags.some((tag) => typeof tag !== 'string')) {
+    fail('"tags" must be a list of strings')
+  }
+
+  return {
+    title: requireString('title'),
+    description: requireString('description'),
+    date: optionalDate('date') ?? fail('"date" is required'),
+    updated: optionalDate('updated'),
+    category: requireString('category'),
+    tags: tags as string[],
+    math: data.math === true,
+    mermaid: data.mermaid === true,
+    draft: data.draft === true,
+    coverImage: optionalString('coverImage'),
+    coverImageAlt: optionalString('coverImageAlt'),
+  }
+}
+
+export function getPostMeta(slug: string): PostMeta {
+  const { data, content } = readMarkdownFile(postsDirectory, slug)
+  return {
+    slug,
+    ...parsePostFrontmatter(slug, data),
+    readingTimeText: readingTime(content).text,
+  }
 }
 
 export function getAllPostsMeta(): PostMeta[] {
-  return getAllPostSlugs()
+  return fs
-    .map((slug) => {
+    .readdirSync(postsDirectory)
-      const fullPath = path.join(postsDirectory, `${slug}.md`)
+    .filter((f) => f.endsWith('.md'))
-      const { data, content } = matter(fs.readFileSync(fullPath, 'utf8'))
+    .map((f) => getPostMeta(f.replace(/\.md$/, '')))
-      const readingTimeText = readingTime(content).text
+    .filter((post) => includeDrafts || !post.draft)
-      return Object.assign({ slug }, {
-        ...data,
-        readingTimeText,
-      } as Omit<PostMeta, 'slug'>)
-    })
     .toSorted((a, b) => (a.date < b.date ? 1 : -1))
 }
 
+export function getAllPostSlugs(): string[] {
+  return getAllPostsMeta().map((post) => post.slug)
+}
+
 export function getNextAndPreviousPosts(slug: string): {
   next: PostMeta | null
   previous: PostMeta | null
@@ -61,13 +126,27 @@ export function getNextAndPreviousPosts(slug: string): {
   return { next, previous }
 }
 
-export async function getPostBySlug(slug: string, postDirectory: string = postsDirectory) {
+// Cached so generateMetadata and the page share one render per request/build
-  const fullPath = path.join(postDirectory, `${slug}.md`)
+export const getPostBySlug = cache(async (slug: string) => {
-  const { data, content } = matter(fs.readFileSync(fullPath, 'utf8'))
+  const meta = getPostMeta(slug)
+  const { content } = readMarkdownFile(postsDirectory, slug)
+  return { meta, ...(await renderMarkdown(content, meta)) }
+})
 
+/** Loads a standalone page (about, projects, ...) from content/pages. */
+export const getPageBySlug = cache(async (slug: string) => {
+  const { data, content } = readMarkdownFile(pagesDirectory, slug)
+  const meta = { title: String(data.title), description: String(data.description) }
+  return { meta, ...(await renderMarkdown(content, data)) }
+})
+
+async function renderMarkdown(
+  content: string,
+  options: { math?: boolean; mermaid?: boolean },
+): Promise<{ content: ReactNode; tableOfContents: TocItem[] }> {
   let processor = remark().use(remarkParse).use(remarkGfm)
 
-  if (data.math) {
+  if (options.math) {
     processor = processor.use(remarkMath)
   }
 
@@ -78,11 +157,11 @@ export async function getPostBySlug(slug: string, postDirectory: string = postsD
     .use(rehypeMark)
     .use(rehypeDefinition)
 
-  if (data.math) {
+  if (options.math) {
     processor = processor.use(rehypeKatex)
   }
 
-  if (data.mermaid) {
+  if (options.mermaid) {
     processor = processor.use(rehypeMermaidSsg)
   }
 
@@ -124,9 +203,7 @@ export async function getPostBySlug(slug: string, postDirectory: string = postsD
   const file = await processor.process(content)
   const rawContentNode = file.result as ReactNode
 
-  const readingTimeText = readingTime(content).text
+  const tableOfContents: TocItem[] = []
-
-  const tableOfContents: { text: string; id: string; level: number }[] = []
   const seenIds = new Map<string, number>()
 
   function withHeadingIds(node: ReactNode): ReactNode {
@@ -161,9 +238,5 @@ export async function getPostBySlug(slug: string, postDirectory: string = postsD
     ? cloneElement(rawContentNode, {}, processedChildren)
     : rawContentNode
 
-  return {
+  return { content: processedContent, tableOfContents }
-    meta: { ...(data as Omit<PostMeta, 'slug'>), readingTimeText },
-    content: processedContent,
-    tableOfContents,
-  }
 }

types/Post.type.ts

@@ -2,12 +2,16 @@ export interface PostMeta {
   slug: string
   title: string
   description: string
+  /** ISO 8601 */
   date: string
+  /** ISO 8601 */
   updated?: string
   category: string
   tags: string[]
   math: boolean
   mermaid: boolean
+  /** Drafts are rendered in development only. */
+  draft: boolean
   readingTimeText: string
   coverImage?: string
   coverImageAlt?: string