Web Crawlers: What You Need to Know

Your website is constantly being crawled by various bots, each serving different purposes. Some of these bots, such as search engine crawlers, help improve your site’s visibility and SEO. Others, like scrapers, may extract data without your consent, potentially harming your site’s performance. Understanding the differences between these bots and knowing how to manage them is crucial for maintaining control over your website’s security and search rankings.

There are two main types of website crawlers:

First-party bots – These are tools that website owners and SEO professionals use to audit, analyse, and optimise their own sites. They help identify technical issues, improve page speed, and ensure proper indexing by search engines. Tools like Screaming Frog and Sitebulb fall into this category.
Third-party bots – These operate externally, often crawling your website without direct permission. Some, like Googlebot, are beneficial, as they index your content for search engines, helping users find your site. However, others, such as competitor scrapers and data harvesters, may extract content for their own use, potentially affecting your rankings and reducing traffic to your pages.

While search engine crawlers are necessary for online visibility, unwanted scrapers can be problematic. Website owners can take steps to manage bot activity, such as using robots.txt directives, monitoring server logs, and implementing security measures like CAPTCHAs or bot-blocking services.

By understanding the different types of website crawlers and their effects, you can take proactive steps to optimise your site while minimising risks associated with harmful bots.

First-party crawlers: Mining insights from your own website

Website crawlers play a crucial role in identifying areas for improving technical SEO. By analysing how search engines interact with your site, these tools can help optimise its structure, enhance indexing, and improve overall performance.

Building a strong technical foundation, ensuring efficient site architecture, and improving crawlability are long-term strategies that contribute to sustained search traffic growth. A well-optimised site makes it easier for search engines to access and rank your content, ultimately leading to better visibility in search results.

In some cases, crawlers may reveal critical issues that could be limiting your site’s performance. For example, a common problem is an outdated robots.txt file on a staging site that unintentionally blocks all search bots, preventing pages from being indexed. Identifying and resolving such errors can lead to immediate improvements in rankings and traffic.

To better understand how to optimise your site’s technical SEO, let’s explore different crawl-based technologies and how they can help improve your website’s search performance.

Googlebot via Search Console

Since Googlebot operates within Google’s infrastructure, you can’t manually trigger it to crawl your site. However, by verifying ownership through Google Search Console (GSC), you can access valuable insights into how Googlebot interacts with your pages. Google provides step-by-step guidance on setting up GSC, making it easy to get started.

GSC is free and offers key data, particularly about page indexing. It also provides insights into mobile-friendliness, structured data, and Core Web Vitals. Although technically a third-party tool, GSC functions similarly to a self-run site crawl, as only verified users can view their site’s data.

Screaming Frog SEO Spider

Screaming Frog is a desktop-based application that generates crawl data for your website. It also offers a log file analyser, which can be useful if you have access to server logs. For this discussion, we’ll focus on Screaming Frog’s SEO Spider.

At $259 per year, Screaming Frog is much more affordable than many cloud-based tools that charge similar amounts per month. However, since it runs locally on your computer, it stops crawling when your device is turned off. Despite this, it delivers fast and accurate data, making it an excellent choice for those who want detailed technical SEO insights.

Using the main interface, you can easily launch website crawls. Once a crawl is complete, exporting the “Internal > All Data” report allows you to analyse the results in Excel or Google Sheets. Screaming Frog also provides various export options, including reports on internal linking, redirects, and mixed content.

One drawback is that Screaming Frog requires hands-on management. Users must be comfortable working with raw data in spreadsheet software to maximise its potential.

Ahrefs Site Audit

Ahrefs is a cloud-based SEO platform that includes a Site Audit module for technical analysis. To use it, you create a project, configure the crawl settings, and let the system scan your site for issues.

Once the audit is complete, Ahrefs provides an SEO health rating (0-100) and highlights key problems. Clicking on an issue offers further details, and helpful guidance is available to explain why fixes are necessary.

Because Ahrefs runs in the cloud, crawls continue even if your computer is turned off, making it more convenient than Screaming Frog. However, its higher cost may not be justifiable if you don’t need its additional features, such as backlink analysis and keyword research.

Semrush Site Audit

Semrush is another cloud-based SEO tool with a built-in technical site audit function. Like Ahrefs, it also includes backlink and keyword research capabilities.

The platform provides a technical SEO health rating, which improves as you resolve detected issues. It highlights errors and warnings, with explanations of why they matter and how to fix them.

Both Semrush and Ahrefs offer powerful site audit features, making it easy to launch crawls, interpret results, and provide recommendations. While both platforms are more expensive than Screaming Frog, they excel at translating crawl data into actionable insights.

For those new to technical SEO, Semrush is slightly more affordable than Ahrefs, making it a solid choice for beginners.