How do search engine crawlers scan a site?

Search crawlers scan a site step by step, like smart but limited guests who have little time and a clear plan.

Here is how it works:

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#1. Choosing starting URLs

A crawler starts with:

• already known pages;
• links from sitemap.xml;
• external links to the site;
• previously visited URLs.

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#2. Checking robots.txt

Before going inside, the bot checks the site.com/robots.txt file and looks at which sections it is forbidden to scan. If you closed off a section, it will not go there.

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#3. Loading the page

The bot loads the HTML, not always waiting for a full JS render. So content that appears dynamically may simply go unnoticed.

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#4. Extracting links

It pulls all internal and external links out of the HTML and adds them to the crawl queue, if they are allowed.

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#5. Repeating and updating

A site is not scanned once and for good. The bot returns regularly:

• more often to active and popular pages;
• less often to static or weakly linked ones.

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#6. Limits (crawl budget)

Every site has its own limit: how many pages, how often, and at what depth to scan. The more errors, duplicates, and clutter, the faster the crawler "leaves".

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#7. Passing data to the index

After scanning, analysis begins:

• which pages to include in the index,
• which content matters,
• which is a duplicate,
• what to remove.

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Summary: A crawler scans strictly by the rules, quickly, and not endlessly. If you want your site to rank well, you need to make it convenient for the crawler: a clean structure, a sitemap, no obstacles.