Which user-agent strings identify HSTS preload bot?

The following user-agent strings identify HSTS preload bot: hstspreload-bot.

Does HSTS preload bot respect robots.txt rules?

According to official documentation, HSTS preload bot does not respect robots.txt rules.

How can I verify HSTS preload bot traffic with live traffic data?

You can verify HSTS preload bot requests by checking your server access logs for the documented user-agent strings. For accurate verification, correlate user-agent patterns with IP ranges or verification methods provided by Chromium.

What is HSTS preload bot?

Direct Answer: The HSTS preload bot, operated by Chromium, checks that links can be preloaded for Chromium.

Operator: Chromium Type: Other Bot Purpose: HSTS preload checking

The HSTS preload bot is a tool used to check if links can be preloaded for Chromium, ensuring that websites can instruct web browsers to access the site only over HTTPS.

User-Agent Identification

The following user-agent strings identify HSTS preload bot in your live traffic data:

hstspreload-bot

robots.txt Rules for HSTS preload bot

Respects robots.txt: No

This bot does not commit to following robots.txt

HSTS preload bot does not officially follow robots.txt directives. The only reliable way to control access is through server-side blocking (IP filtering, user-agent rules in your web server config) combined with log monitoring to verify effectiveness.

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Crawl Behavior

Frequency:Not Documented

Request Pattern:Not Documented

Crawl Activity Index

Relative crawl activity for HSTS preload bot over the past 28 days. Higher values indicate increased crawling intensity compared to the period baseline.

View recent activity data (last 7 days)

Date	Activity Index
Mar 26, 2026	88.0
Mar 27, 2026	82.7
Mar 28, 2026	83.1
Mar 29, 2026	81.8
Mar 30, 2026	87.3
Mar 31, 2026	90.2
Apr 1, 2026	88.8

Source: Cloudflare Radar

Why track HSTS preload bot traffic?

Identify and classify unknown crawler activity. HSTS preload bot may appear in your live traffic data with varying frequency. Tracking its behavior helps you decide whether to allow, throttle, or block it based on actual data.

Protect your crawl budget. Every bot request consumes server resources. Understanding what HSTS preload bot crawls helps you prioritize the crawlers that matter.

Log Verification

To verify HSTS preload bot traffic in your live traffic data:

Search access logs for the user-agent strings listed above
Check if the IP addresses match documented ranges (if provided by Chromium)
Verify the crawl pattern matches documented behavior
Use reverse DNS lookup for additional verification if available

Note: Observed behavior in production environments may differ from official documentation. Live traffic monitoring provides the only reliable verification of actual bot behavior.

Undocumented Information

The following information is not officially documented for HSTS preload bot:

crawl frequency
request pattern
IP verification
JavaScript rendering

Official Documentation

View Official HSTS preload bot Documentation →

Information sourced from official documentation. Content generated with AI assistance.