CAPTCHA or challenge

A test that tries to tell people from bots, such as picking out images or waiting on a “checking your browser” page. Agents can't pass them, so one on arrival or at checkout ends the visit.

Why it matters

A CAPTCHA ends an agent's visit on the spot, because agents can't solve them. In our study of 255 online stores, 6% showed one on the home page, and 15% of the carts and checkouts we could load showed one to every visitor. If you need one, show it only when something looks wrong, not to everyone at checkout.

More terms in getting in

• robots.txt A file at the root of your site that tells crawlers and agents which pages they may visit.
• Bot protection Services such as Cloudflare, Akamai or DataDome that block or challenge automated visitors.
• CDN Content delivery network: the service that sits in front of your site and delivers it quickly around the world.
• Rate limit A cap on how many requests a visitor can make in a given time.
• Verification Checking that a visitor claiming to be a known agent really is, using the proof its operator publishes: IP ranges, reverse DNS or a signature.
• Impostor (spoofed agent) A request that uses a trusted agent's name but fails verification.

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