Dynamic OG Image Generation with Astro

Dynamic OG Image Generation with Astro

Generate social preview images automatically at build time instead of maintaining stale static PNGs. Every share on Twitter/X, LinkedIn, or Slack will show accurate, up-to-date stats.

Why bother

Static OG images go stale. The day you add your 200th template or hit 1k GitHub stars, your social preview still shows the old numbers. Dynamic generation solves this once and stays accurate forever.

The pattern below uses Satori (Vercel) to render a React-like tree to SVG, then resvg to convert to PNG. It runs at build time in Astro — zero runtime cost, no external service.

Stack

Package	Role
satori	Renders JSX-like object tree to SVG
@resvg/resvg-js	Converts SVG to PNG (Rust, fast)
@fontsource/inter	Local font files (woff1 format required)

Setup

pnpm add satori @resvg/resvg-js @fontsource/inter

Create the file at src/pages/og-image.png.ts. Astro automatically serves it at /og-image.png.

Reference it from your layout:

<meta property="og:image" content="/og-image.png" />
<meta name="twitter:image" content="/og-image.png" />

See the ready-to-use template: examples/scripts/og-image-astro.ts

The pattern

import type { APIRoute } from 'astro'
import satori from 'satori'
import { Resvg } from '@resvg/resvg-js'
import { readFileSync } from 'fs'
import { resolve, dirname } from 'path'
import { fileURLToPath } from 'url'

const __dirname = dirname(fileURLToPath(import.meta.url))

export const GET: APIRoute = () => {
  const fontData = readFileSync(
    resolve(__dirname, '../../node_modules/@fontsource/inter/files/inter-latin-400-normal.woff')
  ).buffer as ArrayBuffer

  const svg = satori(
    { type: 'div', props: { style: { /* ... */ }, children: [ /* ... */ ] } },
    { width: 1200, height: 630, fonts: [{ name: 'Inter', data: fontData }] }
  )

  const png = new Resvg(svg, { fitTo: { mode: 'width', value: 1200 } }).render().asPng()

  return new Response(png.buffer as ArrayBuffer, {
    headers: { 'Content-Type': 'image/png' },
  })
}

Dynamic stats from content

Count your content files at build time instead of hardcoding:

function countQuestions(): number {
  const dir = resolve(__dirname, '../content/questions')
  let total = 0
  for (const cat of readdirSync(dir, { withFileTypes: true })) {
    if (cat.isDirectory()) {
      total += readdirSync(resolve(dir, cat.name))
        .filter(f => f.endsWith('.md')).length
    }
  }
  return total
}

Stats you can auto-count:

• Markdown files in a content directory (questions, articles, docs)
• YAML entries in a data file
• Line count of a large document

Stats to keep hardcoded (update manually):

• GitHub stars (dynamic, use 1.1k+ as a conservative label)
• Templates from another repo
• Performance benchmarks

Gotchas

Font format matters

Satori requires woff1 or TTF. It will silently fail or throw an error with woff2 or remote CDN URLs that redirect to HTML.

// Correct — local woff1 from @fontsource
readFileSync('node_modules/@fontsource/inter/files/inter-latin-400-normal.woff')

// Fails — woff2 not supported by resvg
readFileSync('node_modules/@fontsource/inter/files/inter-latin-400-normal.woff2')

// Fails — CDN may return HTML (redirects, auth walls)
await fetch('https://fonts.gstatic.com/s/inter/...')

Static files shadow API routes

Astro dev server serves static files in public/ before API routes. If you have a public/og-image.png, it will always be served instead of your dynamic endpoint.

Delete it:

rm public/og-image.png

Also check the project root and dist/ — files there can shadow the route too. Diagnose with curl -I http://localhost:4321/og-image.png: if the response has a Last-Modified header, you are hitting a static file, not the API route.

Browser cache

After removing the static file, do a hard refresh (Cmd+Shift+R) or test in a fresh incognito window. The browser may have cached the old PNG aggressively.

satori is synchronous in newer versions

Some versions of satori return a Promise<string>, others return string. If you get a [object Promise] PNG, add await:

const svg = await satori(tree, options)

Testing

Local preview — visit directly in the browser:

http://localhost:4321/og-image.png

Social preview simulation — paste your prod URL into:

• opengraph.xyz — generic OG debugger
• LinkedIn Post Inspector (linkedin.com/post-inspector/) — forces cache refresh for LinkedIn
• Twitter Card Validator (cards-dev.twitter.com/validator)

CI check — if you want to catch regressions, you can add a build step that checks the generated PNG file size is above a threshold:

# In CI after pnpm build
SIZE=$(wc -c < dist/og-image.png)
if [ "$SIZE" -lt 10000 ]; then
  echo "og-image.png looks too small ($SIZE bytes) — generation may have failed"
  exit 1
fi

Variants

Personal branding (no stats grid)

children: [
  { type: 'span', props: { style: { fontSize: '48px', color: '#c0522a' }, children: 'FB.' } },
  { type: 'span', props: { style: { fontSize: '80px', fontWeight: 800, color: '#f5f5f5' }, children: 'Your Name' } },
  { type: 'span', props: { style: { fontSize: '24px', color: '#8b949e' }, children: 'Your tagline here' } },
]

Project list badges

['project-a.com', 'project-b.com', 'project-c.com'].map(label => ({
  type: 'div',
  props: {
    style: { background: '#161b22', border: '1px solid #30363d', borderRadius: '8px', padding: '8px 16px' },
    children: [{ type: 'span', props: { style: { color: '#c0522a' }, children: label } }],
  },
}))

Terminal-style badge (for CLI tools)

{
  type: 'div',
  props: {
    style: { background: '#21262d', border: '1px solid #30363d', borderRadius: '20px', padding: '6px 16px', color: '#3fb950', fontFamily: 'monospace' },
    children: '>_ your-cli-tool',
  },
}

Keeping stats in sync

Maintain a single source of truth. When you update stats in the OG image, update them everywhere (landing page badges, README, etc.) in the same commit.

For projects with multiple landings, create a slash command /update-stats-image-landings that walks each repo and prompts you to verify each stat. This prevents drift across sites.