AI bot allowlist vs blocklist strategy
Two strategies for AI bots: a blocklist that allows everything except named bots (default-open), or an allowlist that blocks everything except named bots (default-closed). Each has a different maintenance cost and failure mode as new crawlers appear.
Default-open versus default-closed
A blocklist is default-open: you allow all crawlers and disallow specific named tokens. New crawlers you have never heard of are admitted until you notice and add them. A blocklist is low-friction but leaks: the long tail of new and obscure AI crawlers reaches you by default.
An allowlist is default-closed: you disallow broadly and allow only specific named tokens. New crawlers are excluded until you explicitly approve them. An allowlist is tighter but higher-maintenance, and aggressive broad rules can accidentally exclude crawlers you actually want, such as search engines.
Choosing and maintaining
The right choice depends on your goals and capacity. If broad visibility matters and you can tolerate unknown crawlers, a blocklist of the specific bots you object to is simpler. If control matters more and you can maintain it, an allowlist gives default-closed safety at the cost of ongoing upkeep.
Either way, the strategy is only as good as its currency. New AI crawlers appear regularly, so review your list against what is actually reaching your site. robots.txt remains a request to compliant crawlers, so neither strategy enforces access on its own.
- Blocklist: default-open, low-friction, admits unknown crawlers
- Allowlist: default-closed, tighter, higher maintenance
- Review periodically against crawlers actually observed
How it appears in analytics and logs
Your strategy determines how new, unlisted AI crawlers are treated by default. A blocklist lets unknown crawlers through until you add them; an allowlist excludes them until you approve them. Logs reveal which unlisted crawlers your strategy is currently admitting.
Diagnostic use case
Choose between an allowlist and a blocklist approach for AI bots based on your tolerance for maintenance and for unknown crawlers.
What WebmasterID can help detect
WebmasterID surfaces which AI crawlers actually reach your site, including ones not yet in your robots.txt, so you can keep an allowlist or blocklist current based on observed activity.
Common mistakes
- Choosing an allowlist and accidentally excluding wanted search crawlers with a broad disallow.
- Choosing a blocklist and forgetting it admits every new crawler by default.
- Setting the policy once and never reviewing it as new crawlers appear.
Privacy and accuracy notes
This is a robots.txt strategy topic, not visitor data. The bots discussed are non-human; WebmasterID records them as bot events only, separate from human analytics.
Related pages
- Should you block AI crawlers?
Whether to block AI crawlers is a trade-off between visibility in AI products and control over how your content is used. There is no universally correct answer. This entry lays out the considerations honestly, without legal overclaims, and points to the robots.txt mechanics.
- Undeclared AI scrapers and how they appear
Some AI scrapers do not declare a recognisable token. They appear with generic user agents, browser-like strings, or forged identities. They cannot be identified by a clean token, so the honest approach is to describe the pattern, verify what you can, and categorise conservatively.
- Web crawlers reference
Reference for crawlers, control tokens, and how they appear in traffic.
Sources and verification notes
- MDN — robots.txtBackground on robots.txt allow/disallow semantics underpinning both strategies.
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.