Kavra LabPOST /signupVerifyUnclear case, invisible check first
- New device, no history
- Hosting network, not a home ISP
- Human-like typing and pointer
Risk58
Comparison
CAPTCHA alternatives: stop bots without making people solve puzzles
The main CAPTCHA alternatives are invisible challenges that test the browser instead of the person, proof-of-work that makes each request cost compute, device and behavior intelligence that scores every visit, and risk-based step-up that adds friction only for the risky few. Kavra combines these into one explained risk assessment per visit.
- Kavra approach
- Score every visit, explain it, step up only when unsure
- CAPTCHA approach
- Ask the visitor to prove they are human
- Visitor friction
- None for most people with modern alternatives
- Best for
- Signup, login, checkout, promos, APIs
What can you use instead of a CAPTCHA?
A CAPTCHA asks the visitor to prove they are human. Every alternative flips that around: it asks the traffic to prove itself, quietly, and only involves the person when the evidence is unclear. In practice there are four families of alternatives, and most serious setups combine at least two of them.
Invisible challenges run small tests in the background that a real browser passes without the visitor noticing. Proof-of-work makes the browser spend a little compute before a form submits, which is trivial for one person and expensive for a bot sending thousands of requests. Device and behavior intelligence scores the whole visit: the network, the device, the browser, how the pointer and keyboard move, and what history this device has. Risk-based step-up uses that score to decide who sees friction at all, such as an email code, a one-time password or a short behavioral check.
Why teams are replacing puzzle CAPTCHAs
Puzzles were designed for a time when computers could not read warped text or recognize a bus. That time is over. The cost of a puzzle now falls mostly on the people you want to keep.
- AI solvers and solving services. Image and text models solve many classic puzzles, and paid services forward the rest to human workers who return answers in seconds.
- Friction lands on real customers. Every puzzle costs time at the exact moment you want a signup, a login or a payment to go through.
- Accessibility. Visual puzzles are hard for people with low vision or motor impairments. Audio fallbacks help but add their own friction.
- A pass says little. A solved puzzle tells you someone clicked the right tiles. It does not tell you that the same person has already opened forty accounts from one laptop.
The last point matters most for fraud teams. Many costly attacks, such as multi-accounting and bonus abuse, are run by humans with tools, not by bots that fail puzzles. A human will always pass a CAPTCHA.
Five ways to stop bots without puzzles
Invisible challenges
Background tests check that the browser behaves like the real browser it claims to be. Real users see nothing. See invisible challenge.
Proof-of-work
The browser solves a small computation before submitting. It raises the cost of volume attacks but does not tell a person from a well-funded script.
Device and environment intelligence
Checks whether the device is real or an emulator, virtual machine or spoofed profile, and whether it has been seen before under other accounts.
Behavior analysis
Looks at timing, pointer paths, typing rhythm and navigation. Scripted flows are too regular or too fast; replayed human input has its own tells.
Network intelligence
Separates home and mobile connections from datacenters, VPNs, Tor and residential proxies that borrow real home IPs.
Risk-based step-up
Only visits with mixed evidence get friction, such as a one-time code. Everyone else passes. See step-up authentication.
CAPTCHA alternatives compared
No single approach covers everything. The table shows the trade-offs in plain terms.
| Approach | Visitor friction | Accessibility | Stops well | Can miss | AI solvers |
|---|---|---|---|---|---|
| Visible puzzle CAPTCHA | High for everyone who gets one | Visual tasks exclude some users | Simple scripts | Solving services, humans with tools | Many puzzles solvable by models |
| Invisible score or challenge | None for most visitors | Good, nothing to solve | Automation and fake browsers | Real browsers driven by people | Not relevant, no puzzle to solve |
| Proof-of-work | Small delay, no task | Good | Cheap high-volume floods | Low-volume, high-value abuse | Not relevant |
| Device and behavior intelligence | None | Good | Spoofed devices, automation, repeat actors | Needs tuning for shared devices | Agents show up as automation or declared bots |
| Risk-based step-up | Only for the risky few | Depends on the step chosen | Unclear cases at key actions | Depends on the signal feeding it | Step can be a code, not a puzzle |
Popular CAPTCHA products and how they differ
The best-known products have moved far beyond the original puzzle. Here is where each one sits, based on its own public documentation.
| Product | How it works | Compare with Kavra |
|---|---|---|
| Google reCAPTCHA | Score-based keys return a score with no challenge; checkbox and policy-based keys show image challenges. Now part of Google Cloud Fraud Defense. | Kavra vs reCAPTCHA |
| hCaptcha | Widget with visible and invisible modes. Pro and Enterprise add passive, mostly challenge-free modes and bot scores. | Kavra vs hCaptcha |
| Cloudflare Turnstile | Managed, non-interactive and invisible widget modes built on browser checks such as proof-of-work. Works on any site. | Kavra vs Turnstile |
| Arkose Labs | Bot Manager scores traffic and sends suspicious sessions to MatchKey challenges built to resist AI solvers. | Kavra vs Arkose Labs |
How to replace a CAPTCHA without letting bots in
- 01
Run the new check in observe-only mode
Keep the CAPTCHA while the new signal scores the same traffic. Compare what each would have blocked before you change anything.
- 02
Decide on the server, not in the widget
Verify every token on your backend, bind it to the action (signup, login, checkout) and refuse reused tokens.
- 03
Set three outcomes, not two
Allow clear humans, block clear abuse, and step up the unclear middle. That middle band is where most of the tuning happens.
- 04
Protect the actions that pay out
Signup, login, promo claim, checkout and one-time-password endpoints matter more than a contact form.
- 05
Watch repeat actors, not only bots
Link devices and accounts so that a person who passes every challenge but runs twenty accounts still shows up.
When a simple CAPTCHA is the better fit
A full risk platform is not always worth it. A plain CAPTCHA, or a free invisible widget, is often enough when:
- The form has no money behind it, such as a newsletter signup, a comment box or a low-traffic contact form.
- The main threat is dumb spam from simple scripts, not people using headless browsers, proxies and antidetect tools.
- You have no backend team to act on a risk score and just need a yes or no on one form.
- Budget is zero and volume is low, where free tiers of widget products cover you.
Once a form grants something of value, such as a bonus, a free trial, credits, a discount or access to an account, the question stops being "is this a bot?" and becomes "who is this, and have we seen them before?". That is where a CAPTCHA runs out.
Sources
- reCAPTCHA versions (Google for Developers)
- reCAPTCHA overview (Google Cloud documentation)
- reCAPTCHA key types (Google Cloud documentation)
- hCaptcha developer documentation
- hCaptcha Pro
- Cloudflare Turnstile documentation
- Cloudflare Turnstile widget modes
- Arkose Bot Manager
- AI-resistant challenge design: MatchKey (Arkose Labs blog)
reCAPTCHA is a trademark of Google LLC. Cloudflare and Turnstile are trademarks of Cloudflare, Inc. hCaptcha, Arkose Labs, MatchKey and other names are trademarks of their respective owners. This guide is based on public information as of September 2026 and may change. Kavra Lab is not affiliated with any of these companies.
How Kavra helps
Where Kavra fits among CAPTCHA alternatives
Kavra is a detection and decision service, not a challenge widget. It can replace a CAPTCHA or sit next to one.
Every layer, one assessment
3,000+ data points across network, device, browser integrity, behavior and history, weighed by an AI/ML risk engine that looks for contradictions between layers.
No puzzles, ever
Invisible to real customers. More background checks run when evidence is unclear, with nothing for the visitor to solve.
Explained decisions
Each verdict comes with a plain-language headline, the findings behind it and a recommended action: allow, verify or block.
Repeat actors linked
Returning devices are recognized and one actor behind many accounts is linked, even when the fingerprint rotates.
One script, one call
An async script under 64 KB plus one server call. Observe-only mode shows results before you block anything.
FAQ
Frequently asked questions
Something else? Talk to our team.
What is the best alternative to CAPTCHA?
For most sites it is an invisible check that scores the visit from network, device, browser and behavior signals, combined with a step-up for unclear cases. That keeps friction off real users while still stopping automation. For forms that pay out value, add device and account linking so repeat actors are caught even when they pass every challenge.
Can AI solve CAPTCHAs now?
Many classic image and text puzzles can be solved by current vision models, and solving services cover the rest with human workers. That is why newer products lean on invisible browser checks and risk scores rather than harder puzzles, and why some vendors design challenges specifically to resist automated solvers.
Are invisible CAPTCHAs better for accessibility?
Usually yes, because most visitors never see a task. Accessibility still matters for the fallback: if an invisible check is unsure and shows a visual puzzle, people with low vision or motor impairments can struggle. Check which fallback a product uses and whether it offers audio, text or code-based alternatives.
Is proof-of-work enough to stop bots?
Proof-of-work raises the cost of high-volume attacks like spam floods, because every request needs compute. It does little against low-volume, high-value abuse such as account takeover or bonus farming, where an attacker happily spends a second of CPU per attempt. Treat it as one signal, not a full defense.
Can I use Kavra together with a CAPTCHA?
Yes. Some teams keep an existing widget and add Kavra's server-side assessment for the actions that matter, then lower or remove the widget once observe-only results show the new signal is reliable. Kavra recommends an action and your backend decides, so you control when any challenge appears.
See who is really on your site.
Run Kavra on your own traffic in observe-only mode. No risk to your customers, and a clear report of the fraud it finds.