Nepotistic Pontifex Maximus


    0.8.1 • Public • Published

    A pre-render service for client-side rendered websites

    Use Case

    Some websites are client-side rendered with JavaScript. While this is great for building interactive websites, if not used correctly, it'll definitely hurt the Search Engine Optimization (SEO) and index ranking.

    Most libraries provide a way to do Server-Side Rendering (SSR), which is perfect for SEO. But SSR is not always possible, so a Pre-rendering application such as Rendergun is another solution.

    Rendergun uses a real browser to load your page, download all assets, execute the JavaScript, build the DOM and return the HTML as a string. This string can then be returned as a response to web crawlers such as Google, Bing, DuckDuckGo, etc.

    Pre-rendering is recommended by Google. Visit to learn more.


    • 🚀 Uses a real, stable and up-to-date Chromium (Google Chrome): Built on top of puppeteer, an API for Headless Chrome
    • 👩🏻‍⚕️ Self-healing: Rendergun constantly checks the health of the browser instance and restart it if necessary.
    • ⚡️ Cache: Pages are cached to provide lightning fast responses.
    • 🔀 Skip unnecessary requests: Rendergun can skip requests that are not required for rendering, such as CSS and Images files, which can greatly increase the performance of the rendering process.
    • 🐳 Runs on Docker: Rendergun has an official Docker image. Just pull and run it!

    How to install

    Rendergun can be used as a Node.js CLI or Docker container.

    Rendergun Node.js CLI

    # install rendergun install NPM 
    $ npm i -g rendergun 
    # start rendergun with default configuration 
    $ rendergun

    Rendergun Docker Container

    docker run --name rendergun -p 3000:3000 goenning/rendergun



    • Use Case: Request an HTML rendered version of a webpage
    • HTTP Method: GET or POST
    • Parameters:
    Location Name Default Value Required Comments
    QueryString url Yes which url to pre-render
    Body N/A No Rendergun will skip the initial page load of url and use the content of body to render the page. This is useful if the requestor knows what's the content of url as this can avoid an additional HTTP Request. When set, it should be of type text/html.
    HTTP Header x-rendergun-wait-until load No which chrome event to wait before returning the HTML. Possible values are load, domcontentloaded, networkidle0,networkidle2
    HTTP Header x-rendergun-timeout 10000 No timeout in milliseconds for Chrome to load the page
    HTTP Header x-rendergun-abort-request No a RegExp that aborts all requests that matches it. Useful to skip requests to CSS/Images files that are not required for pre-rendering
    HTTP Header x-rendergun-block-ads false No true/false if Rendergun should skip requests to Ads/Trackers domains. This gives a small performance improvement and avoid unecessary tracking

    Example: is a client-side rendered page built with React. Look at the source and you'll see that only JavaScript files and a JSON object is returned by the server. The whole HTML is built by React when it's executed by the browser.

    Start rendergun and open http://localhost:3000/render?url= on your browser. The visual result should be the same, except that now the server has returned just the HTML content, without the JavaScript files and the JSON object. Web crawlers like Google, Bing and, DuckDuckGo prefer this over client-side rendered pages.


    • Use Case: Check if Rendergun is healthy
    • HTTP Method: GET

    This is used to verify if Rendergun and the Headless Chrome instance are healthy. If everything is OK, 200 status code is returned, otherwise 500. Rendergun will constantly monitor the health of Headless Chrome instance and restart it if necessary.


    Rendergun can be customized by using Environment Variables. The following settings are available.

    Name Default Value Comments
    PORT 3000 which port Rendergun should bind to
    CACHE_MAX_SIZE 100 how many megabytes should Rendergun use for caching
    CACHE_MAX_AGE 1800 how long (in seconds) should items be cached


    npm i rendergun

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    • goenning