Safe Official docs AI & LLM Bots

Mozilla Tabstack

Q: What is the official user-agent string for Mozilla Tabstack?

The official user-agent string for Mozilla Tabstack is: Mozilla-Tabstack . 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 Mozilla Tabstack by performing a reverse-DNS lookup on the source IP.

Q: Is Mozilla Tabstack safe?

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

Q: Will blocking Mozilla Tabstack hurt my SEO?

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

Q: How do I block Mozilla Tabstack in robots.txt?

Add the following lines to your /robots.txt file: User-agent: Mozilla-Tabstack Disallow: / This instructs Mozilla Tabstack 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 Mozilla Tabstack is crawling my site?

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

Operated by Mozilla

Scout's quick take

Mozilla Tabstack visits a page only when a person asks Mozilla's assistant to open it. It is not a background crawler.

# Block only if you really mean to
User-agent: Mozilla-Tabstack
Disallow: /

Check my site for AI bots Build a full robots.txt

Quick Facts

User-Agent:: Mozilla-Tabstack
Category:: AI & LLM Bots
Operator:: Mozilla
Safety:: Safe
Blocking Impact:: Low - No SEO ranking impact
SEO Impact Score:: 2/10
Official docs:: docs.tabstack.ai

Confirmed by the operator

Mozilla names Mozilla-Tabstack on its own documentation page, linked above. The token, purpose and robots.txt behaviour on this profile come from that page, re-checked on October 19, 2026.

What is Mozilla Tabstack?

Mozilla Tabstack is an on-demand AI fetcher operated by Mozilla. 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 Mozilla's assistant.
Mozilla Tabstack uses the user-agent token Mozilla-Tabstack. 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 Mozilla Tabstack?

✅ No SEO Impact - Blocking Mozilla Tabstack does not affect your rankings in Google, Bing, or any other search engine. Mozilla Tabstack 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.

Want to see whether Mozilla Tabstack actually visits you? Read how do I monitor AI bot traffic to my website?

How to block Mozilla Tabstack with robots.txt

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

Block completely (robots.txt)

User-agent: Mozilla-Tabstack
Disallow: /

Allow all (robots.txt)

User-agent: Mozilla-Tabstack
Allow: /

Block private only (robots.txt)

User-agent: Mozilla-Tabstack
Disallow: /private/
Disallow: /api/
Disallow: /admin/
Allow: /

Nginx server block

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

Apache .htaccess

# Apache: Hard-block Mozilla Tabstack
SetEnvIfNoCase User-Agent "Mozilla-Tabstack" 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 Mozilla Tabstack safe to allow?

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

Verify by reverse-DNS lookup: legitimate Mozilla Tabstack requests resolve to Mozilla's domain.

What does Mozilla Tabstack do?

Understanding Mozilla Tabstack'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

Mozilla Tabstack in context

Mozilla Tabstack is a user-triggered agent operated by Mozilla. In plain terms, it fetches a page when a person asks an assistant or app to open it. Our database files it under AI and LLM crawlers and ranks it Tier 2, important crawlers from established AI and search operators. 74 of the 104 AI and LLM crawlers in our database share this tier.

Its safety rating is safe and its blocking impact is low. So the decision about Mozilla Tabstack rests on what you want from Mozilla, not on its behaviour. How we rate safety and impact.

How site owners treat Mozilla Tabstack

Our robots.txt study of the Tranco top 10,000 did not track Mozilla-Tabstack as a named token, so we do not publish an adoption figure for it. If you run a large site, your own logs are the best evidence of how often it visits.

Does it follow robots.txt?

Mozilla Tabstack's operator does not clearly document how it treats robots.txt. Write the Mozilla Tabstack rule anyway, then confirm in your logs that its requests stop.

Mozilla crawlers and close alternatives

Mozilla runs only this one crawler in our database, so a single User-agent: Mozilla-Tabstack group controls everything Mozilla fetches through it.

Other AI and LLM crawlers that do the same job (fetches a page when a person asks an assistant or app to open it) include ChatGPT Agent from OpenAI, ChatGPT Operator from OpenAI, ChatGPT-User from OpenAI, ChatGPT-User/2.0 from OpenAI, Claude-SearchBot from Anthropic, Claude-User from Anthropic. Deciding about Mozilla Tabstack is usually a decision about the whole group, so check how your file treats these too.

We first recorded Mozilla-Tabstack on September 22, 2026. Mozilla documents it on docs.tabstack.ai, and we recheck that page before each release.

Which rule Mozilla Tabstack actually follows

Mozilla Tabstack reads exactly one group in robots.txt, the most specific one that names Mozilla-Tabstack, and never combines rules across groups. This short file shows the trap:

User-agent: *
Disallow: /private/

User-agent: Mozilla-Tabstack
Disallow: /drafts/

Find the group. Mozilla Tabstack looks for a group naming Mozilla-Tabstack. One exists, so it ignores User-agent: * completely.
Apply only that group. It is refused /drafts/ and nothing else.
The surprise. /private/ is open to Mozilla Tabstack, because that rule lives in the * group it no longer reads. To keep it out of both, repeat Disallow: /private/ inside its own group.

Test yourself: does a rule under User-agent: * apply to Mozilla Tabstack if the file also has a User-agent: Mozilla-Tabstack group?

No. Once a group names it, Mozilla Tabstack reads only that group. Put every rule you want it to follow inside its own group.

Test yourself: will blocking Mozilla Tabstack remove your pages from AI answers?

Often, yes. Mozilla Tabstack is a user-triggered agent, so pages it cannot fetch can drop out of the answers or results it supports.

Test yourself: is User-agent: mozilla-tabstack the same as User-agent: Mozilla-Tabstack?

Yes. RFC 9309 makes user-agent matching case-insensitive. Paths are a different story: Disallow: /Blog/ does not block /blog/.

Should you allow Mozilla Tabstack? Decide by situation

Recommended setting for Mozilla Tabstack by type of site
If you are...	Recommended setting
You publish content and want AI answers to cite it	Allow it. Mozilla Tabstack fetches pages for answers, so blocking it can remove you from them.
You license content and want to stop AI training	Blocking it does not stop training, because Mozilla Tabstack is a user-triggered agent. Block the operator's training crawler instead.
You run an online shop	Allow it on product and category pages, which are the pages shoppers ask assistants about.
Your server is under load from bots	Rate-limit before blocking. It is rated safe in our database.

Check Mozilla Tabstack on your own site

Open /robots.txt on your domain and search for Mozilla-Tabstack. If it is not named, it follows User-agent: *.
List the Disallow lines in the group Mozilla Tabstack follows and test your key URLs against them; the longest match wins, and Allow wins a tie.
Look beyond the file. A firewall or bot manager can refuse Mozilla Tabstack even when robots.txt allows it, and that never shows in the file.
Run our AI crawler access test to see how Mozilla Tabstack and every other crawler we track are treated in one pass, including firewall refusals.

Common mistakes with Mozilla Tabstack

The errors we see most often with Mozilla Tabstack in the files and firewalls we test:

Assuming a robots.txt rule will stop Mozilla Tabstack. User-triggered fetches act for a person, and some operators say robots.txt may not apply to them. Check the operator's statement above.
Blocking Mozilla Tabstack as if it were a bulk crawler. It fetches one page because a person asked; blocking it means that person's assistant cannot read your page.
Counting Mozilla Tabstack visits as crawl volume. Each request maps to a real user question, which makes the paths it requests a useful signal of what people ask about you.

All three hide inside a file that looks correct, so check Mozilla Tabstack from outside after every change.

Spotting Mozilla Tabstack in your logs

robots.txt says what Mozilla Tabstack may do; your access logs show what it actually did.

Count requests

On a server with standard Nginx or Apache logs, this counts matching requests per day (adjust the log path for your host):

grep -iE "Mozilla-Tabstack" /var/log/nginx/access.log \
  | awk '{print $4}' | cut -d: -f1 | sort | uniq -c

And this shows which paths it requested most, which is the quickest way to see whether your Disallow lines are being respected:

grep -iE "Mozilla-Tabstack" /var/log/nginx/access.log \
  | awk '{print $7}' | sort | uniq -c | sort -rn | head -20

Check the requests are genuine

Anyone can send the Mozilla Tabstack user-agent, so confirm the source before acting on a match:

Mozilla-Tabstack: we hold no published IP list, so use reverse DNS where the operator documents a hostname and treat an unverifiable Mozilla Tabstack request with caution.

Frequently Asked Questions

What is the official user-agent string for Mozilla Tabstack?

The official user-agent string for Mozilla Tabstack is: Mozilla-Tabstack. 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 Mozilla Tabstack by performing a reverse-DNS lookup on the source IP.

Is Mozilla Tabstack safe?

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

Will blocking Mozilla Tabstack hurt my SEO?

How do I block Mozilla Tabstack in robots.txt?

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

User-agent: Mozilla-Tabstack
Disallow: /

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

Does Mozilla Tabstack respect robots.txt?

Mozilla Tabstack is operated by Mozilla 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 Mozilla Tabstack is crawling my site?

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