Web Rendering: Impact on SEO

Definition

The process by which the browser or search engine transforms HTML, CSS, and JavaScript code into a visual web page.

Rendering is the process by which a browser or search engine bot transforms source code (HTML, CSS, JavaScript) into a visual and interactive web page. For SEO, rendering is crucial because it determines what Google actually sees on a page. Google performs rendering in two phases: first it crawls the raw HTML, then it renders the JavaScript (Web Rendering Service). Rendering can be client-side (in the browser), server-side (on the server), or hybrid (SSG, ISR).

Rendering Page rendering Web rendering

Key Points

Google uses the Web Rendering Service to execute JavaScript
Server-side rendering (SSR) is preferable for SEO
Critical content should be in the initial HTML for fast indexing

Practical Examples

Client-side rendering

A React site using CSR sends a nearly empty HTML and generates all content via JavaScript. Google must wait for JS rendering to see the content, causing indexing delays.

Pre-rendering

A service like Prerender.io detects bots and serves them a pre-rendered HTML version, while users receive the interactive JavaScript version.

Frequently Asked Questions

What is the difference between CSR and SSR?

CSR (Client-Side Rendering) generates content in the browser via JavaScript. SSR (Server-Side Rendering) generates the complete HTML on the server. SSR is better for SEO because Google receives the content directly.

Does Google render JavaScript the same way as a browser?

Google uses a headless version of Chrome, but rendering is deferred and has limitations (no local storage, timeout for long-running scripts). It is not identical to a user browser.

Related Terms

Go Further with LemmiLink

Discover how LemmiLink can help you put these SEO concepts into practice.

LemmiLink Home Development expertise for agencies