Guides / Go
Pages with custom social cards get measurably more clicks than a generic logo when shared on X, LinkedIn or Slack. Designing one image per blog post by hand doesn't scale — RasterKit renders them from an HTML template with {{variables}} you fill from Go.
Design the card once (plain HTML/CSS — gradients, fonts, avatars), store it as a template, then request /v1/image with a title and author per page. Combine with signed URLs and your og:image tag can point directly at the API.
Sign up free (magic link, no card) — your key is shown right after sign-in. You get 100 renders/month free across screenshots, PDFs, and images.
Store a template once (dashboard or POST /v1/templates) — HTML/CSS with
{{variables}} — then render it with per-page values:
package main
import (
"bytes"
"fmt"
"io"
"net/http"
"os"
"time"
)
func main() {
body := []byte(`{"template_id": "tpl_your_template", "variables": {"title": "Hello World", "author": "Paul"}}`)
req, _ := http.NewRequest("POST", "https://rasterkit.com/v1/image", bytes.NewReader(body))
req.Header.Set("x-api-key", os.Getenv("RASTERKIT_API_KEY"))
req.Header.Set("content-type", "application/json")
client := &http.Client{Timeout: 60 * time.Second}
res, err := client.Do(req)
if err != nil {
panic(err)
}
defer res.Body.Close()
data, _ := io.ReadAll(res.Body)
if res.StatusCode != 200 {
panic(fmt.Sprintf("render failed: %d %s", res.StatusCode, data))
}
os.WriteFile("og-image.png", data, 0644)
fmt.Println("Saved og-image.png")
}The response body is the file itself — no JSON envelope to unwrap, no second download request. Errors come back as JSON with a stable error code.
The OG Image API reference documents every parameter. The ones people reach for first:
width/height — defaults to the OG standard 1200×630device_scale_factor: 2 — retina-sharp textcache_ttl: 604800 — published posts don't change; cache for 7 days freeog:image straight at the API1200×630 (the default) renders crisply everywhere — X, Facebook, LinkedIn, Slack, iMessage. Use device_scale_factor: 2 for retina-sharp text.
Yes — {{variable}} values are HTML-escaped by default. Use triple braces {{{variable}}} only for trusted markup.
Yes — load Google Fonts or any @font-face in your template; the engine waits for fonts to be ready before capturing.