Koa middleware for Prerender.io. Intercepts requests from bots and crawlers and serves prerendered HTML, so your JavaScript-rendered app is fully indexable by search engines and social media scrapers.

Compatible with Koa v2+ and Node.js 18+.

Installation

npm install prerender-koa

Usage

const Koa = require('koa');
const prerender = require('prerender-koa');
const app = new Koa();
app.use(prerender({
  token: 'YOUR_PRERENDER_TOKEN'
}));
// your other middleware and routes

The middleware intercepts bot requests and proxies them to Prerender.io, returning prerendered HTML. Regular browser requests pass through unaffected. All responses include an X-Prerender: true/false header.

Options

Option	Type	Default	Description
`token`	`string`	`process.env.PRERENDER_TOKEN`	Your Prerender.io token
`serviceUrl`	`string`	`process.env.PRERENDER_SERVICE_URL` or `https://service.prerender.io/`	Prerender service URL (use this for self-hosted Prerender)
`protocol`	`string`	`null`	Force a protocol (`http` or `https`). Defaults to the request's protocol

Environment variables

PRERENDER_TOKEN=your_token_here
PRERENDER_SERVICE_URL=https://service.prerender.io/  # optional

Self-hosted Prerender

app.use(prerender({
  serviceUrl: 'http://your-prerender-server:3000'
}));

How it works

Requests are prerendered when all of the following are true:

The HTTP method is GET
The User-Agent matches a known bot/crawler (Googlebot, Bingbot, Twitterbot, GPTBot, ClaudeBot, etc.)
— OR the URL contains _escaped_fragment_
— OR the X-Bufferbot header is present
The URL does not end with a static asset extension (.js, .css, .png, .woff2, .webp, etc.) — matched case-insensitively

Everything else passes through to your normal Koa middleware.

License

MIT