How Search Engines Work
See how search engines discover, understand and serve web pages to users.
To rank on a search engine, you first need to understand how it works. Every search engine runs three core jobs.
1. Crawling
Automated bots called crawlers or spiders (Google's is Googlebot) follow links across the web to discover pages.
2. Indexing
The engine analyzes each page it finds - the text, images, and structure - and stores what it learns in a giant database called the index.
3. Ranking
When someone searches, the engine picks the most relevant, highest-quality pages from its index and orders them on the results page.
The key takeaway
If a page is not crawled, it cannot be indexed. If it is not indexed, it can never rank. Everything in SEO builds on these three steps.
Example
# See how Googlebot identifies itself in server logs
Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)
# You can test how Google renders a page with the URL Inspection tool
# in Google Search Console.When to use it
- A developer adds an internal link from a high-authority page to a new blog post so Googlebot follows it and discovers the post faster.
- A media site uses fast server response times to ensure Googlebot can crawl more pages within its daily crawl budget.
- A retailer avoids JavaScript-only product descriptions so the search engine renderer can read content without executing scripts.
More examples
Permissive robots.txt for Googlebot
A permissive robots.txt with a Sitemap directive ensures Googlebot can discover and crawl all intended pages.
# /robots.txt — allow all bots to crawl everything
User-agent: *
Disallow:
# Point bots to the sitemap
Sitemap: https://example.com/sitemap.xmlServer-side rendered product HTML
Serving fully rendered HTML ensures search engines index actual content rather than empty JavaScript shells.
<!-- Without SSR: crawler sees empty container -->
<!-- <div id="product-list"></div> -->
<!-- With SSR: crawler reads full content immediately -->
<div id="product-list">
<article data-sku="SH-001">
<h2>Trail Runner Pro</h2>
<p>Lightweight shoe for off-road running.</p>
<span class="price">$129.99</span>
</article>
</div>Measure server response time as Googlebot
A slow TTFB reduces the pages Googlebot crawls per visit; this command shows what response time the crawler actually experiences.
# Time the server as seen by Googlebot
curl -o /dev/null -s \
-w "TTFB: %{time_starttransfer}s Total: %{time_total}s HTTP: %{http_code}\n" \
-A "Googlebot/2.1 (+http://www.google.com/bot.html)" \
https://example.com/products/trail-runner-pro/
Discussion