Fastify

FastifyFastify

Generate a unique OG image for every page, or any on-demand graphic, from a single Imejis template. The pattern below uses a Fastify route handler as a thin proxy: your API key stays on the server, and the browser (and social crawlers) only ever see your own URL.

Set two environment variables first: IMEJIS_API_KEY (from your dashboard) and IMEJIS_DESIGN_ID (any design's ID).

.env

IMEJIS_API_KEY=your_api_key
IMEJIS_DESIGN_ID=your_design_id

1 a handler that renders the image1. A handler that renders the image

This handler takes a title query param, POSTs it to Imejis as a component.property override, and sends the finished image back as a Buffer. Because the key is sent server-side, it never reaches the client.

server.js

import Fastify from "fastify"
 
const fastify = Fastify()
 
fastify.get("/og", async (request, reply) => {
  const title = request.query.title ?? "Untitled"
 
  const upstream = await fetch(
    `https://render.imejis.io/v1/${process.env.IMEJIS_DESIGN_ID}`,
    {
      method: "POST",
      headers: {
        "dma-api-key": process.env.IMEJIS_API_KEY,
        "Content-Type": "application/json",
      },
      body: JSON.stringify({ "headline.text": title }),
    }
  )
 
  const image = Buffer.from(await upstream.arrayBuffer())
 
  reply.header("Content-Type", "image/jpeg")
  // Renders are deterministic, so cache aggressively at the edge/CDN.
  reply.header(
    "Cache-Control",
    "public, immutable, no-transform, max-age=31536000"
  )
  return reply.send(image)
})
 
await fastify.listen({ port: 3000 })

2 point your metadata at it2. Point your metadata at it

Reference the handler from whatever renders your page's <head>, passing each page's real data. Social platforms fetch /og?title=… from your own domain, no key exposed.

head.html

<meta
  property="og:image"
  content="https://your-site.com/og?title=Hello%20from%20Fastify"
/>
<meta name="twitter:card" content="summary_large_image" />

Override any field. Each dynamic component exposes keys like headline.text, title.color, or image.image. Send only the ones you want to change. A design's overridable fields are listed in its Share / API panel.