Bots now generate more than half of HTML requests, Cloudflare reported in its 2025 Year in Review, with AI crawlers among the fastest-growing of them. They fall into two broad jobs. Training crawlers like GPTBot or Bytespider gather data to build models. Search and retrieval crawlers like OAI-SearchBot or PerplexityBot fetch live pages that get cited in answers. Blocking the first protects training data; blocking the second removes you from AI answers.
Most respect robots.txt, so you can allow or disallow each by name. The most common visibility failure is not a deliberate block but a WAF or bot-management rule that catches AI crawlers as collateral, leaving pages reachable to browsers but invisible to the engines writing answers.
Letting the right crawlers in is also the first step to making a site agent-ready, so an AI agent can act on the page and not just read it.