Cap
Cap: A privacy-focused web CAPTCHA for teams prepared to host and operate it themselves. Ranked #24 of 32 in CAPTCHA Software by our editors (6.6/10); pricing: Free plan; best for privacy-focused developers self-hosting a web CAPTCHA.
At a glance
- Editor score6.6 / 10
- PricingFree plan
- Best forPrivacy-focused developers self-hosting a web CAPTCHA
- Free planYes
- Paid fromFree
- CAPTCHA modesProof-of-work
- Facts checked22 Oct 2026
Where it wins
- Keeps verification on your deployment without cookies or tracking.
- Combines proof-of-work with JavaScript and browser checks.
- Offers a reCAPTCHA-compatible siteverify API and multiple site keys.
Where it doesn't
- Self-hosting means the deployer bears infrastructure costs.
- Its verified scope is web-focused, with web SDK support.
- Challenge variety is limited, and support is through documentation.
Our verdict on Cap
Cap is an open-source CAPTCHA for websites that need bot protection without sending visitor data to a third party. It is aimed at developers who want to self-host verification and control how the CAPTCHA runs. The browser widget can execute challenges invisibly in the background, using proof-of-work and time-lock challenges alongside dynamically generated JavaScript and browser instrumentation checks. A dashboard supports multiple site keys, and the project is Apache 2.0 licensed.
The main fit question is deployment and ecosystem scope. Cap provides a standalone backend, Docker-based deployment, customizable web components, and a reCAPTCHA-compatible siteverify API. Those pieces suit a web integration that can operate its own backend; the documented SDK scope is web. Self-hosting also puts infrastructure responsibility with the deployer, so Cap is less suited to teams seeking a vendor-managed CAPTCHA service or a deployment outside its web focus.
Privacy is a notable design choice: Cap is described as using no cookies, tracking, or third-party verification calls. Its challenge mix includes proof-of-work, GPU-resistant time-lock challenges, and browser checks, but challenge variety is limited. The project documents privacy, accessibility, and regulatory considerations for self-hosted deployments. It is a strong candidate for privacy-focused developers comfortable operating their own CAPTCHA service; teams that need broader challenge variety or managed operations should consider alternatives. The pricing model is open source, with infrastructure costs borne by whoever deploys it.
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Cap pricing
Cap fact sheet
| Free plan | Yes |
|---|---|
| Paid from | Free |
| CAPTCHA modes | Proof-of-work |
| Audio challenge | No |
| Accessibility options | Yes |
| Monthly verifications | Not verified |
| SDK platforms | Web |
| Privacy controls | Yes |
| Deployment | Self-hosted, Browser extension |
| Platforms | Web |
| Compliance & security | GDPR, HIPAA |
| Support | Docs |
| Built for | Solo, Small business, Mid-market, Enterprise (editorial estimate) |
| Pricing | Free plan |
| Website | capjs.js.org |
| Facts checked | 22 Oct 2026 |
Alternatives to Cap
- Cloudflare TurnstileA free CAPTCHA alternative with adaptive checks, invisible modes and server-side validation.9.4
- Google reCAPTCHAAdaptive bot protection with web and Android options and a free monthly allowance.9.2
- Alibaba Cloud CAPTCHAA managed CAPTCHA service with regional per-call pricing and policy controls.9.0
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Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
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