Open Source vs. Paid
ALTCHA has one free, open-source core, and two paid ways to run more on top of it — Cloud (we host it) and Sentinel (you host it). All three block bots using the same proof-of-work engine underneath; the paid plans add a layer that decides when to ask more of a visitor. See How ALTCHA Works for that concept in more detail.
The one-sentence version
- Open-source — free forever, you run it, the same invisible check for every visitor.
- Cloud — adds adaptive, risk-based protection, fully managed by us.
- Sentinel — everything in Cloud, plus more of the platform, running on your own infrastructure.
What's free forever
The open-source widget and libraries include, at no cost and with no sign-up:
- No cookies or tracking
- GDPR & CCPA compliant
- WCAG 2.2 AA accessible
- Proof-of-work verification
- Self-hosted, with full data ownership
- MIT licensed — use it however you like
This is a complete, production-ready CAPTCHA replacement on its own. See Quick Start to add it to your forms.
What Cloud adds
On top of the open-source core, Cloud adds adaptive protection, fully managed by us on EU servers — no setup, no maintenance, live in minutes:
- Adaptive, risk-based challenges (only ask more from visitors who look suspicious)
- Real-time threat intelligence
- A hosted dashboard with analytics
What Sentinel adds
Sentinel includes everything in Cloud, plus additional platform features exposed via its API — such as the Classifier — since it runs the full engine rather than a subset of it. Sentinel runs on your own infrastructure, giving you full data sovereignty, with the option to run entirely air-gapped.
You can move between the open-source core, Cloud, and Sentinel later without changing your widget integration — see Pricing for exact plans and rates.
Which one should I choose?
- Just getting started, or want it free forever → the open-source widget.
- Want it managed, with no server to run yourself → Cloud.
- Need full control over your infrastructure and data (compliance, air-gapped environments, etc.) → Sentinel.
For a more detailed breakdown by use case, see Solutions.
Next steps
- Quick Start — add the open-source widget to your forms
- Cloud — get started with the managed service
- Sentinel — self-host the full platform
- Pricing — compare plans and pricing