Mozilla-Tabstack user agent
Operated by Mozilla
Mozilla-Tabstack is a user agent reported for Tabstack, a Mozilla service that reads web pages for AI tools.
The Mozilla-Tabstack bot at a glance
- Mozilla-Tabstack is operated by Mozilla and fetches a page when a person asks an AI assistant about it or shares its link, and fetches pages to power a specific product feature.
- The robots.txt token for Mozilla-Tabstack is Mozilla-Tabstack.
- Blocking an AI assistant fetcher has no effect on search rankings.
- Mozilla-Tabstack robots.txt support: Yes.
- Recommendation for Generative Engine Optimization (GEO): Your choice.
What is Mozilla-Tabstack?
Public registries describe it as performing programmatic, AI-driven page fetches.
Public registries report that it follows robots.txt.
Should you block Mozilla-Tabstack?
Blocking Mozilla-Tabstack is a business decision: it protects your content but can lower how well AI products know your brand.
| Effect on search rankings | Blocking an AI assistant fetcher has no effect on search rankings. |
|---|---|
| Effect on AI visibility | Blocking stops the assistant from reading your page when a user asks about it or pastes your link, so its answer falls back to other sources. |
| Follows robots.txt | Yes |
| Recommendation | Your choice |
How to block or allow Mozilla-Tabstack
Put the robots.txt rule in the file at the root of every domain and subdomain, for example https://example.com/robots.txt. The token Mozilla-Tabstack is matched case-insensitively.
robots.txt: block
# Block Mozilla-Tabstack
User-agent: Mozilla-Tabstack
Disallow: /robots.txt: allow
# Allow Mozilla-Tabstack
User-agent: Mozilla-Tabstack
Allow: /robots.txt: partial
# Keep Mozilla-Tabstack out of private areas only
User-agent: Mozilla-Tabstack
Disallow: /wp-admin/
Disallow: /cart/
Disallow: /checkout/
Disallow: /my-account/
Allow: /Nginx
# Nginx: return 403 to Mozilla-Tabstack
if ($http_user_agent ~* "(Mozilla\-Tabstack)") {
return 403;
}Apache
# Apache .htaccess: return 403 to Mozilla-Tabstack
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} (Mozilla\-Tabstack) [NC]
RewriteRule .* - [F,L]Cloudflare WAF
# Cloudflare > Security > WAF > Custom rule, action: Block
(http.user_agent contains "Mozilla-Tabstack")How to verify real Mozilla-Tabstack traffic
Mozilla publishes no IP list or reverse DNS pattern for Mozilla-Tabstack, so the user agent cannot be verified. Anyone can send the same string. Rate-limit unusual volume instead of trusting the name.
How to find Mozilla-Tabstack in your server logs
Search the web server access log for the token. The command below counts Mozilla-Tabstack requests per URL on Nginx or Apache.
grep -i "Mozilla-Tabstack" access.log | awk '{print $7}' | sort | uniq -c | sort -rn | head -20For a full report per AI bot, upload the log to the AI Log File Analyzer, a free tool by Justin Hà.
Mozilla-Tabstack FAQ
Mozilla-Tabstack uses the robots.txt token "Mozilla-Tabstack". Mozilla does not publish a full user-agent string, so match the token inside the User-Agent header.
Yes. Mozilla states that Mozilla-Tabstack follows robots.txt rules written for the "Mozilla-Tabstack" token.
Blocking an AI assistant fetcher has no effect on search rankings. Blocking stops the assistant from reading your page when a user asks about it or pastes your link, so its answer falls back to other sources.
Add two lines to the robots.txt file at the root of each domain and subdomain: "User-agent: Mozilla-Tabstack" followed by "Disallow: /". The token is case-insensitive. Changes can take up to 24 hours to be picked up.
Not reliably. Mozilla publishes no IP list or reverse DNS pattern for Mozilla-Tabstack, so anyone can send the same user agent. Rate-limit unusual volume instead of trusting the name.
Search your server access log for "Mozilla-Tabstack", for example with: grep -i "Mozilla-Tabstack" access.log. The AI Log File Analyzer by Justin Hà counts visits per AI bot from an uploaded log file.
Sources: Public bot registry. Last reviewed by Justin Hà.
See which of these bots actually reach your website
The AI Log File Analyzer by Justin Hà counts visits from GPTBot, ClaudeBot, PerplexityBot and other AI crawlers in your server log, for free. The GEO Technical Package sets up robots.txt, llms.txt and crawler access for AI search.
