HTML to PDF in Go

Send HTML (or a URL) to the FrameForge API and get a PDF back. It is rendered in real Chromium, so modern CSS, web fonts and JavaScript all work. No browser to install or babysit.

The code

Go standard library. Set FRAMEFORGE_KEY to your API key.

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"time"
)

func main() {
	body, _ := json.Marshal(map[string]any{
		"html":   "<h1>Invoice #1001</h1><p>Total: £49.00</p>",
		"format": "pdf",
		"width":  794, // A4 at 96 DPI
		"height": 1123,
	})
	req, _ := http.NewRequest("POST", "https://api.frameforgeapi.com/render", bytes.NewReader(body))
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("X-API-Key", os.Getenv("FRAMEFORGE_KEY"))

	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 != http.StatusOK {
		panic(fmt.Sprintf("render failed: %d %s", res.StatusCode, data))
	}
	os.WriteFile("invoice.pdf", data, 0o644)
}

How it works

• POST /render takes JSON with exactly one of html (up to 1 MiB) or url, plus format (png, jpeg or pdf), width and height (1 to 3840 px) and fullPage.
• The response body is the file itself (application/pdf), not JSON, so write the bytes straight to disk or stream them to the user.
• Page size: the PDF page is width × height pixels. 794 × 1123 is A4 at 96 DPI and 816 × 1056 is US Letter. Content longer than one page flows onto more pages of the same size. With fullPage: true you get one tall page instead.
• Margins: pages have no printer margins, so add padding in your HTML (for example body { padding: 48px }).
• Caching: identical requests within 24 hours are served from cache and don't count against your quota. Check the X-FrameForge-Cache response header.
• Errors come back as JSON with an error code: 401 bad key, 429 rate limited, 400 blocked_url for private or local addresses.

Rendering a URL instead of HTML

{"url": "https://example.com/report", "format": "pdf", "width": 1280, "height": 800, "fullPage": true}

Doing it yourself instead

chromedp drives Chrome from Go without external dependencies, and Gotenberg is a self-hosted Docker service for HTML-to-PDF.

An API makes sense when you don't want Chromium on your servers, or when you need images (PNG/JPEG) and PDFs from the same call. If you render a few PDFs a month on a server you already run, self-hosting is perfectly reasonable.

Free tool: Website to PDF. Other languages: Node.js · Python · PHP · Ruby · Java · C# / .NET · curl / Bash · Next.js · Laravel · Django · Ruby on Rails