Brave Search Help

Proof of Work captchas

As opposed to the current captchas where a user is required to solve a simple challenge, Proof of Work (PoW) captchas require a person’s computer to solve a mathematical problem with little to no user interaction. The design is inspired by the Bitcoin Proof of Work.

Why do we have captchas

We would never show a captcha to a user in a world with no bots. Bots are programs often pretending to be real users by exhibiting similar behaviour, in order to scrape Brave Search results. We want to have a mechanism which allows to block bots after identifying them while giving normal users an ability to get through in case they are misclassified. That’s what captchas are used for.

We are working to improve the detection of bots and adjusting the difficulty with which challenges are solved such that it is harder for bots and easier for legitimate users to get back to Brave Search.

Why is a different kind of captcha needed

Brave Search has long relied on captchas to allow users to get through the firewall after having been flagged as bots. Although the rate of false positives is observed to be low, users of popular VPNs can still be classified as bots from time to time. The design of a common captcha requires a user to solve some kind of a graphical challenge.

Although such challenges seem simple enough, they have some drawbacks:

  • the failure rate is still very high, indicating that some users do not manage to solve them appropriately,
  • they waste users’ time and energy, while the goal is to impact bots only.

Proof of Work captchas allow to bother users less by requiring less interaction while still making it expensive for bots to scrape Brave Search.


The design of the captcha follows the strict privacy protecting principles of Brave. It relies neither on a third-party nor on any private information.