Crawling is the initial step in a search engine finding your website’s content. Without crawling, your site won’t be indexed or ranked, resulting in no traffic.
Google announced in 2016 that they have knowledge of 130 trillion pages, a process that is remarkably complicated and completely automatic.
However, research from Ahrefs shows that 96.55% of content receives zero traffic from Google. This indicates that search engines like Google only crawl and index select content.
What is Search Engine Crawling?
Web crawling, as defined by Google, involves discovering and downloading text, images, and videos from online web pages using search engine web crawlers, also known as spiders. Web crawling ensures that these bots efficiently index content for search engine visibility.”
These crawlers find new pages by travelling through URLs (links). They crawl sitemaps, internal links and backlinks to find additional pages that haven’t been crawled. Once they find a new page, they extract the information to index it in their database.
Different Search Engine Bots & User Agent Strings
Search engine bots are crucial to understand search engine crawling, and recognizing user agent strings related to those search engine bots enhances this knowledge.
Web crawlers, or bots, are automated tools that find new web pages across the internet. By identifying themselves with user-agent strings, they help index online content for better search engine results.
Blocking access means no rank on search engines!
| Search Engine | Bot Name | User Agent String Example | Purpose |
| Googlebot | Googlebot/2.1 (+http://www.google.com/bot.html) | Googlebot crawls and indexes web pages to help improve Google Search results and other Google services. | |
| Bing | Bingbot | Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm) | Bingbot explores and indexes web pages to enhance Bing Search results. |
| DuckDuckGo | DuckDuckBot | DuckDuckBot/1.0; (+http://duckduckgo.com/duckduckbot.html) | DuckDuckBot scans and indexes web pages to make DuckDuckGo Search better. |
| Yandex | YandexBot | Mozilla/5.0 (compatible; YandexBot/3.0; +http://yandex.com/bots) | YandexBot crawls and indexes web pages to improve Yandex Search. |
| Baidu | Baiduspider | Mozilla/5.0 (compatible; Baiduspider/2.0; +http://www.baidu.com/search/spider.html) | Baiduspider searches and indexes web pages to enhance Baidu Search. |
| Apple | Applebot | Applebot/1.0 (+http://www.apple.com/go/applebot) | Applebot explores and indexes web pages for services like Spotlight Search. |
The Stages of Search Engine Crawling
Search engines work through a process called crawling to deliver relevant search results. This involves five steps: discovery, prioritization, crawling, data extraction, and indexing.
Step One: Discovery
The URL discovery process kicks off web crawling. When starting out, search engines like Google use bots, like Googlebot, to track down new, uncrawled pages.
Optimizing crawlability is crucial because search engines typically have a huge queue of URLs waiting to be crawled. Ensuring your page gets crawled the first time highlights the importance of optimizing crawlability.
Search engine crawling involves several methods to discover new content.
Primarily, search engines might re-crawl previously indexed URLs for updates or changes. Additionally, they crawl a website’s XML sitemap to uncover new pages.
Another approach search engines utilize involves crawling internal and external links to identify new pages.
Remember, however, “Crawling is not a guarantee you’re indexed.” – Rand Fishkin
Search engine indexing ensures your web pages are added to search results, but it’s not automatic. Your pages must meet specific criteria for search engines to index them.
Step Two: Fetching
Search engine crawlers kick off by picking a URL from their list. They then request the page from the web server, grabbing and indexing its content to boost search engine results.
HTML code is sent by the server as the page’s content, usually in HTML format. This HTML code includes the page’s structure and text. Additionally, HTML code may contain links to other resources like images, CSS, stylesheets, and JavaScript files.
Step Three: Parsing
Web crawling is the process by which search engine bots, known as crawlers, fetch webpages to gather information for indexing. During this process, the crawler parses the HTML content of a page to extract key data, including links, which play a central role in discovering new content.
Key Steps in Web Crawling
- Fetching the Page
When a crawler visits a page, it downloads the HTML code and other associated files. This initial step allows the crawler to analyze the structure and content of the webpage. - Extracting Links
Crawlers identify links embedded within the HTML. These links include both internal links, which connect to pages within the same website, and backlinks, which point to external websites. Extracted links are added to a queue for future crawling. - Re-crawling Existing Pages
Crawlers regularly revisit pages they already know about to ensure their index reflects the most current version. Updates to content, new links, or changes in structure are captured during these re-crawls. - Building the Crawl Queue
URLs found during the link extraction process are prioritized in a crawl queue. This queue determines the order in which new or updated pages will be fetched, balancing factors such as content freshness, relevance, and importance.
Continuous Discovery and Updates
Through this iterative process, crawlers systematically uncover and revisit publicly available webpages. Any page linked from another becomes part of the crawler’s reach, ensuring a comprehensive and regularly updated index of the web.
By understanding how this system operates, website owners can optimize their pages for better visibility. Clean HTML, clear internal linking structures, and high-quality backlinks help ensure that pages are easily discoverable and indexed.
Step 4: Rendering
Web crawlers struggle with accurately reading content on modern websites built using JavaScript. This makes it tricky for them to interpret and index such sites correctly.
To understand a webpage completely, search engines need to render it first. This means they run the JavaScript code on the page, much like how a browser would show it to you. This step is crucial for search engines to grasp the full content and present it correctly.
Web crawlers gain a better understanding of web page content, including dynamically generated elements, through this.
However, when web crawlers encounter an HTTP error such as HTTP 500, their crawl efficiency may decrease. During these instances, web crawlers typically adjust their crawl rate to prevent server overload.
Step 5: Indexing
Search engine indexing is when a search engine stores information from web pages in its index.
This helps the search engine’s algorithms decide which pages are most relevant to show when you search for something.
How Do Changes to Page Content Affect Indexing?
Updating a webpage’s content can change how search engines rank and display it. These adjustments impact several areas, from how often search engines visit your site to how users find and interact with your content.
Search engines revisit websites periodically to check for updates. Significant changes, such as adding fresh material or reworking existing sections, are more likely to catch their attention. For instance, if you expand a blog post by adding new research, search engines may see the update as a reason to reassess the page.
Changes to the text, images, or metadata also affect how relevant your page is to specific search queries.
Adding keywords that reflect what your audience is searching for can improve visibility.
For example, replacing generic descriptions with phrases your customers might type into Google, such as “affordable online courses,” can help align your content with their needs.
Adjusting the structure of your page—like revising headings or improving HTML formatting—makes it easier for search engines to understand your content.
Tools like schema markup can highlight key details, such as product information or event dates, which helps search engines present your page in ways that stand out.
Internal links, which connect pages within your site, play a crucial role in guiding search engines.
Updating these links to point to newer or more relevant content can improve how your site is indexed. For example, linking from a high-traffic article to a new service page can boost visibility for both.
Finally, updating meta titles and descriptions changes how your page appears in search results.
A concise, compelling title with relevant keywords can make your page more appealing to users.
If your meta description highlights benefits or solutions, users are more likely to click, which can influence your rankings over time.
Every update is an opportunity to refine how your page serves both search engines and users. By focusing on content quality, clear structure, and thoughtful keywords, you can ensure that your changes are noticed and valued.
Crawling vs. Indexing
Crawling and indexing are often confused in SEO, but they are distinct processes. Knowing how each works is key to optimizing your website effectively.
Here’s a side-by-side comparison to help:
| Feature | Crawling | Indexing |
| Definition | The process of discovering new or updated web pages | The process of storing and organizing information from web pages |
| How it works | Automated bots, known as crawlers, follow hyperlinks to explore web content | Bots analyze the content of crawled pages and extract essential information |
| Sources | Hyperlinks, sitemaps, and URL submissions | Pages that have been crawled |
| Goal | To collect data from web pages for inclusion in the index | To create a structured and searchable database of web content |
| Control | The robots.txt file provides guidance to crawlers on which pages to access | The robots.txt file dictates which pages can be indexed |
| Outcome | A comprehensive list of URLs | A searchable database that facilitates efficient retrieval of search results |
How Search Engines Discover and Index Web Pages
Discovery is the first step in getting your content indexed by search engines. Crawlers, the bots responsible for indexing, use several methods to locate new pages and updates on your site.
Crawlers frequently discover pages by following links.
When a bot finds a link on an indexed page, it may follow that link to uncover new content.
This process allows search engines to explore the web dynamically, relying on the interconnected nature of pages to expand their coverage.
Sitemaps offer another way for crawlers to find your pages.
These files act as directories, listing the URLs on your site and guiding bots to content they might not otherwise reach.
If you have recently added new pages or sections, updating your sitemap ensures these are on the crawler’s radar.
For faster results, tools like Google Search Console let you submit URLs directly.
This method is particularly useful when you’ve made substantial updates or published time-sensitive content.
By manually submitting URLs, you can signal to search engines that these pages are ready for indexing without waiting for crawlers to discover them organically.
While manual submissions work well for a few pages, sitemaps are better suited for handling larger volumes.
Google recommends using XML sitemaps to manage extensive content, as they provide a structured way to communicate updates.
It’s worth noting that Google processes individual URL submissions and sitemaps with similar indexing speeds, so either approach can work depending on your needs.
To ensure crawlers find your most important pages, maintain a strong internal link structure, keep your sitemap updated, and use manual submissions when necessary.
This combination helps search engines stay current with your site’s content and ensures your updates are visible to users as quickly as possible.
Indexing
Understanding how search engines discover and index web pages is key to making your site visible online. Here’s how it works: search engines use bots to crawl links and sitemaps, or you can manually submit pages through tools like Google Search Console.
During the search engine optimization process, search engines analyze various index factors for SEO efficiency, such as content quality, relevance, and keyword usage.
SEO also prioritizes title tags, meta descriptions, and header tags (H1, H2, etc.). Internal and external links, image alt text, page load speed, mobile-friendliness, structured data, and social signals play pivotal roles in SEO.
Additionally, the freshness of content, domain authority, trustworthiness, user engagement metrics, and robots.txt file demands contribute significantly to SEO. T
here are numerous SEO factors determining web pages’ indexing efficacy; for a comprehensive list, refer to Google’s 200 Ranking Factors from Backlinko.
FAQ
How often do search engine crawlers revisit web pages?
Crawlers prioritize pages based on how often they’re updated and how relevant the content appears. For example, a page that regularly adds new information, like a blog or news site, is likely to be revisited more often than one with static content. Search engines also factor in the number and quality of links pointing to a page, both internally from your site and externally from other websites.
Regular updates, like refreshing product descriptions or adding new blog posts, show search engines that your site is active and worth monitoring closely. Crawlers use this activity to assess whether a page’s content has changed enough to warrant re-indexing.
Can search engine crawlers access non-text files like images and videos?
Yes, they can! While search engines can’t directly interpret images, videos, or audio in the way humans do, they rely on associated information to understand and index these files.
How Search Engines Handle Non-Text Files
When crawlers encounter non-text content, they extract details from filenames, alt text, captions, and the text surrounding the file. For example:
- An image with the filename
blue-widget.jpgand alt text “Blue Widget for Sale” gives search engines clues about its content and relevance. - Video metadata, such as titles and descriptions, provides context for indexing and ranking.
Although search engines can’t “read” these files, they still have the potential to rank in search results. Indexed images, videos, and audio can drive significant traffic when paired with relevant metadata and content.
Making Non-Text Files SEO-Friendly
To maximize visibility, ensure your files are named descriptively, use detailed alt text, and provide captions or transcripts where applicable. For videos, consider uploading sitemaps or structured data, which can make it easier for search engines to index and rank them appropriately.
For those curious about specifics, Google provides an online resource detailing the types of files it can index. By aligning with these guidelines, you can improve how search engines process and rank your non-text content, ensuring it contributes effectively to your site’s overall performance.
How do search engines discover new pages?
Search engines find new pages using crawlers. These crawlers track down pages by following links within a site, links from other sites, sitemaps, and sometimes through manual submissions. This way, search engines can efficiently discover new content.
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