Project Mariner (Google): User Agent & robots.txt Rules

Q: What is the official user-agent string for Project Mariner?

The official user-agent string for Project Mariner is: GoogleAgent-Mariner. Use this exact string in robots.txt, Nginx, Apache, or Cloudflare firewall rules to target this bot. Matching in robots.txt is case-insensitive. Verify a request genuinely comes from Project Mariner by performing a reverse-DNS lookup on the source IP.

Q: How do I block Project Mariner in robots.txt?

Add the following lines to your /robots.txt file: User-agent: GoogleAgent-Mariner Disallow: / This instructs Project Mariner not to crawl any path on your site. To block only specific sections, replace / with the path (e.g., Disallow: /blog/).

Q: How do I verify if Project Mariner is crawling my site?

Search your web server access logs for the string GoogleAgent-Mariner (case-insensitive: grep -i "GoogleAgent-Mariner" /var/log/nginx/access.log). Filter by user-agent in your log analytics tool (GoAccess, AWStats, etc.).

Quick Facts

User-Agent:: GoogleAgent-Mariner
Category:: AI & LLM Bots
Operator:: Google
Safety:: Safe
Blocking Impact:: Low - No SEO ranking impact
SEO Impact Score:: 2/10
Official docs:: developers.google.com

What is Project Mariner?

Project Mariner is an on-demand AI fetcher operated by Google. It retrieves a page only when a user explicitly asks an AI assistant or agent to read, summarize, or act on a specific URL. Because it is triggered by real user intent rather than bulk crawling, blocking it mainly prevents users from pulling your content into Google's assistant.

Project Mariner is an on-demand AI fetcher operated by Google. It retrieves a page only when a user explicitly asks an AI assistant or agent to read, summarize, or act on a specific URL. Because it is triggered by real user intent rather than bulk crawling, blocking it mainly prevents users from pulling your content into Google's assistant. Project Mariner uses the user-agent token GoogleAgent-Mariner. You can control it via robots.txt, meta tags (noai), or the emerging llms.txt standard. Robots.txt is voluntary; for hard enforcement, combine it with server-level IP blocking.

What happens if you block Project Mariner?

✅ **No SEO Impact** - Blocking Project Mariner does not affect your rankings in Google, Bing, or any other search engine. Project Mariner is an AI crawler, not a traditional search indexer. You can freely block it via User-agent / Disallow: / without any SEO penalty.

Generally safe to allow; provides legitimate crawling value.

How to block Project Mariner with robots.txt

<code>User-agent: GoogleAgent-Mariner</code> - Matching is case-insensitive. Robots.txt is fetched from the root of each subdomain separately.

Block completely (robots.txt)

User-agent: GoogleAgent-Mariner
Disallow: /

Allow all (robots.txt)

User-agent: GoogleAgent-Mariner
Allow: /

Block private only (robots.txt)

User-agent: GoogleAgent-Mariner
Disallow: /private/
Disallow: /api/
Disallow: /admin/
Allow: /

Nginx server block

# Nginx: Hard-block Project Mariner
if ($http_user_agent ~* "GoogleAgent-Mariner") {
    return 403 "Bot blocked";
}

Apache .htaccess

# Apache: Hard-block Project Mariner
SetEnvIfNoCase User-Agent "GoogleAgent-Mariner" bad_bot
Order Allow,Deny
Allow from all
Deny from env=bad_bot

Meta robots tag

X-Robots-Tag header

X-Robots-Tag: noindex, nofollow

Is Project Mariner safe to allow?

Yes, Project Mariner is a **safe and legitimate** crawler operated by Google. It follows the Robots Exclusion Protocol (RFC 9309) and can be controlled with standard robots.txt rules.

Verify by reverse-DNS lookup: legitimate Project Mariner requests resolve to Google's domain.

What does Project Mariner do?

Understanding Project Mariner's purpose helps you decide whether to allow or block it.

Fetches a page only when a user asks an AI assistant to read it
Summarizes or extracts the URL the user provided
Triggered by real user intent, not bulk crawling
Low traffic volume compared with training crawlers
Blocking it prevents users from pulling your content into the assistant

Frequently Asked Questions

What is the official user-agent string for Project Mariner?

The official user-agent string for Project Mariner is: GoogleAgent-Mariner. Use this exact string in robots.txt, Nginx, Apache, or Cloudflare firewall rules to target this bot. Matching in robots.txt is case-insensitive. Verify a request genuinely comes from Project Mariner by performing a reverse-DNS lookup on the source IP.

Is Project Mariner safe?

Yes, Project Mariner is a **safe and legitimate** crawler operated by Google. It follows the Robots Exclusion Protocol (RFC 9309) and can be controlled with standard robots.txt rules.

Will blocking Project Mariner hurt my SEO?

✅ **No SEO Impact** - Blocking Project Mariner does not affect your rankings in Google, Bing, or any other search engine. Project Mariner is an AI crawler, not a traditional search indexer. You can freely block it via User-agent / Disallow: / without any SEO penalty.

How do I block Project Mariner in robots.txt?

Add the following lines to your /robots.txt file:

User-agent: GoogleAgent-Mariner
Disallow: /

This instructs Project Mariner not to crawl any path on your site. To block only specific sections, replace / with the path (e.g., Disallow: /blog/).

Does Project Mariner respect robots.txt?

Project Mariner is operated by Google and is expected to fetch and parse /robots.txt before crawling, following RFC 9309. For hard enforcement, combine robots.txt with server-level IP or user-agent blocking.

How do I verify if Project Mariner is crawling my site?

Search your web server access logs for the string GoogleAgent-Mariner (case-insensitive: grep -i "GoogleAgent-Mariner" /var/log/nginx/access.log). Filter by user-agent in your log analytics tool (GoAccess, AWStats, etc.).