Understanding Crawling User Agents: Your SEO Guide to Spiders

Alexandre Hoffmann 28/05/2024 7 minutes

Ever found yourself worried about how search engine bots interact with your website? Worried about what “crawling user agents” mean for your site’s SEO? Whether you’re doing your own SEO or looking to work with an SEO agency, understanding these crawlers is crucial. You’re in the right place.

Let’s explore the nuts and bolts of crawling user agents, breaking down technicalities in a conversational, easy-to-digest way.

What exactly are crawling user agents?

Crawling user agents, called spiders or bots, are automated software programmes search engines use to index web content.

When it comes to SEO, understanding these agents is crucial.

They help search engines, like Google, discover and rank pages on your site.

Imagine them as digital librarians. They’re tasked with cataloguing the vast volumes of the internet, ensuring that your content is sortable, accessible and retrievable.

The role of crawling user agents in SEO

Why should you care about these bots?


They directly impact your site’s visibility on search engines.

Here’s a story for you.

Imagine you’ve penned the best article on “sustainable farming practices”. It’s insightful, packed with data and visually appealing.

But if the crawling user agents don’t index it properly, it might never reach its intended audience.

A well-optimised site ensures these agents can effectively crawl and index your pages, enhancing your visibility on search engines.

How to identify crawling user agents

Spotting user agents might seem like a task for Sherlock Holmes. But it’s simpler than you think. When a bot visits your site, it leaves behind a unique “signature” in your server logs.

Here’s a sample log entry: - - [22/Jun/2023:00:00:05 +0000] "GET /robots.txt HTTP/1.1" 200 1234 "-" "Googlebot/2.1 (+http://www.google.com/bot.html)"

This line tells you a lot.

  • The IP address of the bot ( points to Google
  • The user agent information (Googlebot/2.1) confirms it’s Google’s crawler

SEO best practices for crawling user agents

Now that we’re acquainted with user agents, let’s discuss some best practices for optimising these bots.

1. Robots.txt file

This tiny file can make or break how bots interact with your site.

A well-configured robots.txt file tells spiders which pages they can or can’t visit.

Here’s a simple example.

User-agent: *
Disallow: /private/

This snippet tells all user agents to avoid the /private/ directory.

2. Sitemaps

Sitemaps are like roadmaps for bots.

They guide them efficiently through your site.

Make sure to:

  • Update your sitemap regularly
  • Add your sitemap to your robots.txt file
  • Submit your sitemap to search engines

3. Avoiding crawling traps

Ever heard of crawling traps?

These are endless loops that waste crawler resources.

Ensure your URLs are clean, without parameters that can trap bots in loops.

For instance:

  • Using session IDs in URLs can confuse bots
  • Avoid calendar pages that generate infinite URLs

4. Mobile optimisation

Google’s mobile-first indexing means bots prioritise mobile versions of sites.

So, ensure your site is mobile-friendly.

Use tools like Google’s Mobile-Friendly Test to check and optimise.

Dealing with crawling issues

Even with the best practices, issues can crop up.

How do you spot and resolve them?

1. Crawl errors

Google Search Console is your friend here.

Under the “Coverage” report, you can see:

  • Errors due to pages being “Not Found” (404 errors)
  • Redirect issues
  • Pages blocked by robots.txt

2. Crawl budget

Ever heard of a crawl budget?

It’s the number of pages a search engine spider will crawl on your site within a given time.

For vast websites, managing this budget is crucial.

Make sure to prioritise crawling and indexing for critical pages.

3. Duplicate content

Duplicate content can confuse crawlers.

Use canonical tags to indicate the primary version of a page.

Here’s a quick tip: Consistently update old content. It provides fresh signals to bots, enhancing crawl efficiency.

Understanding why your SEO crawler user agent was blocked

First, let’s figure out why your SEO crawler user agent might be blocked in the first place.

There could be several reasons, including:

  1. Robots.txt restrictions: The site might have specific directives that disallow certain user agents
  2. IP blocking: Your crawler’s IP address might be blocked due to excessive requests
  3. Bot detection mechanisms: Some websites use sophisticated methods to block bots, including behaviour analysis and CAPTCHAs

Now, onto the solutions.

Step 1: Check the robots.txt file

First, you should examine the robots.txt file of the website you’re trying to crawl.

This file is typically found by appending /robots.txt to the domain name (e.g., example.com/robots.txt).

Look for entries that might be blocking your user agent.

Here’s an example:

User-agent: YourCrawlerBot
Disallow: /

If you see something like this, your user agent is explicitly disallowed.

You might need to contact the site owner and request permission to get around this.

Step 2: Review IP blocking

If the robots.txt file looks clear, your next step is to investigate IP blocking.

Some websites block IP addresses if they detect excessive requests quickly.

Try crawling at a slower rate.

If you’re using a fixed IP, consider using a range of IP addresses to distribute the requests.

Alternatively, use proxy servers to mask your IP.

Step 3: User agent strings

Some websites might be blocked based on your user agent string.

Update your SEO crawler’s user agent string to mimic a legitimate user agent like a common web browser.

Here’s an example of a user agent string for Google Chrome:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.3

Consider ethical considerations: Always respect the website’s terms of service you’re crawling.

Step 4: Implementing crawler best practices

If you’re repeatedly getting blocked, it’s a sign that you might need to fine-tune your crawling strategy.

Here are some best practices:

  • Crawl rate limiting: Set reasonable limits on how frequently your crawler requests pages. Use crawl delay settings in your crawler’s configuration
  • Respect ‘Retry-After’: If you encounter HTTP 429 status codes, respect the Retry-After header
  • Monitor response codes: Monitor HTTP status codes. A high rate of 403 or 429 codes can indicate blocking
  • Human-like behaviour: Try mimicking human browsing patterns and avoiding high request rates during office hours

Step 5: Contacting the owner of the site

When all else fails, a direct approach often helps.

Reach out to the webmaster or the support team of the site you’re trying to crawl.

Explain who you are and why you need to crawl their site and assure them of the non-disruptive nature of your crawling activities.

Sometimes, just obtaining explicit permission can resolve the issue.

What to do when it’s Cloudflare blocking my crawler

Alright, dealing with Cloudflare blocking your crawler can be tricky, but it’s definitely manageable. Cloudflare is a popular web infrastructure and security company that provides DDoS mitigation, Internet security and distributed domain name server services. When Cloudflare blocks your SEO crawler, it’s usually because it identifies your requests as potentially harmful or spammy.

Let’s get straight into the steps you can take to resolve this issue.

Step 1: Understanding Cloudflare’s blocking reasons

Cloudflare uses various security measures to protect websites from malicious bots and DDoS attacks. These measures include rate limiting, IP blocking and behavioural analysis. Knowing this, let’s break down how to navigate around these issues.

Step 2: Rate limiting

Cloudflare often blocks crawlers due to excessive requests in a short period.


  • Throttle your requests: Slow your crawling rate to make fewer requests per second. Set a rate limit that mimics human browsing behaviour.
  • Randomise your requests: Introduce randomness in your crawling patterns to avoid detection.

Step 3: IP blocking and proxies

Cloudflare might block specific IP addresses if they detect suspicious activity.


  • Rotate IP addresses: Use a pool of IP addresses instead of a single IP
  • Whitelist the IPs of your crawlers
  • Proxy servers: Implement proxy servers to distribute your requests across multiple IPs

Step 4: Custom headers and user agent strings

Cloudflare can block traffic based on user-agent strings or headers.


  • Spoof user agent: Change your crawler’s user agent string to mimic a legitimate browser. For example, use a commonly recognized browser agent like:Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.3
  • Add genuine headers: Include headers that resemble real traffic. This can include RefererAccept-Language, etc.

Step 5: Dealing with JavaScript challenges

Cloudflare often employs JavaScript challenges (CAPTCHAs) to block bots.


  • Headless browsers: Use headless browsers such as Puppeteer or Selenium that can execute JavaScript and mimic real browsing behaviour. These tools can wait for the JavaScript challenges to complete before continuing

Step 6: Cloudflare’s “I’m Under Attack” mode

Robots and crawlers will face heavier scrutiny if Cloudflare has activated “I’m Under Attack” mode.


  • Contact site owners: Ask the website administrators for permission to whitelist your crawler. Provide them with IP addresses, user agents and details about your crawling activities

Step 7: Monitoring and analytics

Consistently reviewing your crawler’s activities and responses can provide insights if Cloudflare begins blocking your IP.


  • Monitor logs: Regularly check the HTTP status codes returned by the server. Pay attention to 403 (Forbidden) or 429 (Too Many Requests) responses
  • Adjust as necessary: Use the data in your logs to adjust your crawler’s behaviour, ensuring it stays under Cloudflare’s radar

The solution checklist

Understanding Cloudflare’s security measures requires a balanced blend of technical adjustments and trial and error. Here’s a quick summary if Cloudflare is blocking your crawler:

  1. Throttle your requests: Slow down your crawling
  2. Whitelist the IPs of the crawler you are using
  3. Rotate IPs or use proxies: Distribute your traffic
  4. Modify headers and user agents: Make your traffic appear more legitimate
  5. Use headless browsers: Handle JavaScript challenges
  6. Contact site owners: Request whitelisting
  7. Monitor responses: Monitor your logs and adjust your behaviour accordingly

Remember: A well-optimised website for crawling user agents is a website primed for SEO success. Following the tips and strategies outlined here will open doors to better search engine visibility and attract a wider audience for your content.

If you’re still facing challenges, don’t hesitate to get in touch! We’ll be more than happy to guide you on the right path for optimal SEO performance.