Invisible reCAPTCHA, reCAPTCHA v3 and Cloudflare Turnstile all promise bot protection your visitors never see — and each keeps that promise for most visitors, then quietly breaks it for the ones it isn't sure about. SpamKill puts nothing in front of the form. It decides after capture, at 99.9% accuracy, and a flagged real person verifies in one step and comes straight through.
Invisible for every visitor, not most: no badge, no widget, nothing to solve — and a record of every blocked submission, reviewable depending on your plan.
Three real products answer to the name. Here's what each one does — fairly stated.
All three share one design decision: they are gates. A gate has to judge the visitor before the form is submitted — so when it's wrong about a real person, the submission never exists, and there is nothing to recover and no record it happened.
"Invisible" describes the median visitor's experience. The cost doesn't disappear — it concentrates on a minority you never hear from.
SpamKill isn't a CAPTCHA that hides well — it's not a CAPTCHA. Nothing stands in front of the form, so nothing can stop a real person from submitting.
The rows that matter — starting with what happens to a real person each one gets wrong.
Want the whole category, competitors included? The CAPTCHA alternatives comparison covers eight options, from the free DIY route up. Leaving reCAPTCHA specifically? Start at the reCAPTCHA alternative page.
A swap, not a stack — a flagged real person can always verify straight through, so the switch doesn't cost you leads.
A CAPTCHA that tries to verify visitors without showing them a challenge. In practice the term means one of three products: Google's invisible reCAPTCHA badge (v2 without the checkbox — the puzzle appears only on suspicion), reCAPTCHA v3 (never shows anything; returns a 0.0–1.0 score your team acts on), and Cloudflare Turnstile (silent browser checks, with an interactive check when it isn't sure). "Invisible" describes the default experience, not a guarantee — each one still challenges or turns away the visitors it can't classify.
For most visitors, yes. But the invisible badge version still triggers image puzzles whenever it's unsure, and v3 hands you a score with nothing built in for the real person who scores low — Google's own guidance is to add your own verification step. It also isn't invisible to your page or your privacy policy: the badge, Google's script on every protected page, and the data flow to Google all remain.
Less than visible puzzles for the median visitor — that's the genuine improvement. The cost concentrates on the minority who score poorly: people on VPNs, privacy browsers, assistive technology, shared office networks, and older devices. They get challenged or quietly turned away, and because none of these tools keeps a record of the real people they reject, that loss never appears in any report.
Yes. Score-based systems are gamed with clean residential IPs and real-browser automation that accumulates a normal-looking history, and when a fallback puzzle does appear, solver services pass it for pennies. SpamKill scores behaviour on the form itself — timing, movement, and input cadence, signals a bot can't outsource — at 99.9% accuracy across 100M+ submissions screened.
No — it's invisible, but it isn't a CAPTCHA. There is no badge, no widget, and no gate deciding who may submit: your visitors see a normal contact form. SpamKill decides after the submission is captured, so nothing is ever lost to the decision — a flagged real person verifies in one step and comes straight through, and depending on your plan you can review everything that was blocked.
Don't — swap, not stack. Even an invisible gate keeps turning some real people away before SpamKill can capture and verify them, so stacking the two keeps exactly the silent losses you came here to remove. Put SpamKill on the form, take the CAPTCHA off the same form, and judge the blocked queue on your own traffic during the 30-day free trial — no credit card. Site-level bot management at your CDN is a different layer and can stay.
Compare the whole category:
That's the difference between an invisible CAPTCHA and no CAPTCHA: one hides the gate, the other removes it. Swap SpamKill in for the 30-day trial, watch the blocked queue on your own traffic, and let real people just hit send. No card required.