Free proof-of-work difficulty tester for signup forms

Proof-of-work spam protection asks the visitor's browser to do a little arithmetic before a form is accepted. Too easy and bots ignore the cost; too hard and a visitor on an old phone waits. Run the real solver here to see how long each difficulty takes on this device.

How to read it

Each added bit doubles the average work, so 18 bits takes about four times as long as 16 bits. Times vary a lot from run to run, because finding a solution is luck (the table shows how many tries each run needed), so look at the average over several runs rather than one. Under half a second is invisible next to typing an email address. Past two seconds, expect people to notice, and test on the slowest phone your audience uses before going higher. Solving runs in a background thread, so the page stays responsive; if your site forbids blob workers in its content security policy, it falls back to the main thread and the page pauses briefly.

This tests only the solver, on your device. It says nothing about whether a bot would be deterred: proof of work raises the cost of each automated attempt but does not tell a bot from a person. The guide Stop subscription bombing on a static site's signup form covers what else to combine it with, and Signup Shield Kit includes the Worker that checks the proof.