Web Crawler: What It Is and How to Optimize a Website for It
How web crawlers work
In simple terms, a website crawler is a program that works behind the scenes of search engines like Google and Yandex, looking for pages for them.
Search engines use special algorithms to show us the most important and relevant results. If a robot cannot scan a page, the search engine will decide that it is irrelevant. As a result, it will be ranked lower in the search results.
The process is similar to how a librarian adds new books to a catalog. If the librarian doesn’t know about a book, it won’t appear in the catalog, and it will be hard for people to find it.
How crawlers process a resource
A search engine robot perceives a website quite differently than we do. Instead of images and text visible to us, it looks at technical details such as the page title, server response, IP address, and others.
The "spider" evaluates many criteria, including: HTTP status code, web server type, timestamp in GMT format, MIME content type, byte size, presence of Keep-Alive, address, redirection response code, server IP address, cookies set, and link structure.
If the website contains a special file with a site map (sitemap.xml), the search robot always reviews it first. This document tells the crawler what to check on the site (and what should not be crawled).
If you want the search "spider" to definitely check a specific section on your website, add the site to the database of a special tool. For example, in Yandex.Webmaster or Google Search Console, there is a feature where you can specify the exact address of the page you want to be indexed.
After the robot accesses the page, it scans it. It reads all the text, examines the HTML code, and finds all the links.
Once the robot finishes examining the page, it sends all the data to the server. There, all unnecessary elements are removed from the collected information, and it is organized in a specific order. Then, the data is sent to a special database known as an index. Although indexing is handled by a different program, it is often also referred to as a search robot.
Search engines process new websites at different speeds. Yandex adds fresh pages to the results after a few days, while Google can do it within just a couple of hours. If the site is brand new and search engines don't know anything about it yet, full site indexing will take much longer — often months.
Search robots don’t just visit a website once. They constantly monitor changes on it. If a page has been deleted or moved, the crawler will inform the search engine. How often robots check the site depends on the size of the website, the number of visitors, and how frequently fresh information appears on the site.
Common issues with web crawlers
Below, we’ll discuss the difficulties that can arise with web crawlers:
- It takes a long time. If the site is large and complex, with a huge number of pages and sections, the search robot will require a lot of time to fully index it. This is especially true for websites with a confusing structure and insufficient internal links between sections. In this case, the process of full indexing can take months. Additionally, errors in the website code and the presence of duplicate pages also slow down indexing and negatively impact its results. This will lead to some sections of the site not appearing in the results or ranking in lower positions.
- It overloads the website. Search crawlers that constantly visit the site create a load on the server. This happens because the robots mimic the actions of real users. If there are too many "spiders," the server may become overwhelmed, rendering the site inaccessible. Popular search engines typically avoid overloading websites, but if a lot of new pages are added to the site at once, the load increases significantly. In this case, you should either manually limit the number of visits by crawlers or configure the server to send "spiders" an overload signal (code 429). This code tells them to reduce the frequency of requests.
- It can be dangerous. If the site owner doesn’t restrict access to certain pages, the search "spider" will find and index them. Due to privacy setting errors or the absence of no-index rules, materials that should not be published may appear online. For example, client data could become accessible through search engines.
- Sometimes crawlers fail to index pages. This issue can arise for several reasons — we’ll explain them below.
Why web crawlers can't see pages
Below, we’ll discuss some of the most common reasons a page isn’t indexed and how to address these issues.
No other pages link to it.
- You’ve intentionally blocked search engines from indexing this section using special tags or the robots.txt file.
- The page is not listed in the sitemap
- Your site takes too long to load.
Add links to the desired section from other parts of your site.
Include the page in the sitemap.
- Check server errors in the indexing report in Google Search Console or using a tool like Screaming Frog.
- Fix all broken links and remove unnecessary redirects.
- Eliminate duplicate pages to avoid confusing search engines.
How to optimize your site for web crawlers
Below, we’ll explore in detail how to make your site more readable for robots.
Conclusion
A web crawler is a software agent that explores resources. It analyzes the content of site sections to identify keywords and assess how pages are interconnected. The information gathered is used by search engines to build an index, making it easier to find relevant pages in response to user queries.
To ensure your site ranks high in search results, it is essential to optimize it according to search engine algorithm requirements.
