PowForge Captcha vs ALTCHA
ALTCHA is a great self-hosted CAPTCHA. It blocks dumb bots with a SHA-256 proof-of-work gate,
works without WASM, and respects user privacy. But it only knows two states:
human or bot. It can't tell the difference between a casual visitor and a
high-value customer who would happily pay 3 sats to skip the puzzle.
PowForge adds a Lightning skip tier on top of the same PoW approach —
so committed users clear in under a second, and you don't pay a
€99-€799/mo subscription to do it.
Both PowForge and ALTCHA use SHA-256 proof-of-work in pure JavaScript (no WASM). The algorithm is not the differentiator. The billing model is. ALTCHA's commercial Sentinel tier is a flat monthly subscription that requires their cloud. PowForge stays fully self-hosted, charges per solve in sats, and lets paying users skip the puzzle entirely via L402 Lightning. Run them together — ALTCHA at the edge for free, PowForge for the high-value endpoints where you want a payment tier.
How ALTCHA and PowForge Captcha compare
| Feature | ALTCHA | PowForge Captcha |
|---|---|---|
| Lightning skip tier | No | Yes — 3 sats skips PoW |
| L402 integration | No | Yes — built in |
| Pricing model | Sentinel: €99–€799/mo flat | Free + pay-per-solve sats |
| Hash algorithm | SHA-256 (default) / PBKDF2 | SHA-256 |
| WASM required | Optional (memory mode) | No |
| npm package | Yes | Yes — drop-in UMD |
| Self-hosted | Yes (Sentinel requires cloud) | Fully self-hosted |
| Source | Open source (MIT) | Open source (MIT) |
ALTCHA Sentinel pricing per altcha.org/sentinel. Both projects use Web Crypto SHA-256 in pure JavaScript by default — algorithm differentiation is not the wedge. Billing model is.
Drop-in alongside ALTCHA
You can keep ALTCHA on the surfaces where free PoW is enough. On the high-value endpoints — registration, paid API actions, premium search — add PowForge to give paying users the Lightning skip tier. Four lines of HTML:
<!-- Works alongside ALTCHA — adds Lightning skip tier -->
<script src="https://captcha.powforge.dev/widget.js"
data-server="https://your-server.com"
data-l402="true"></script>
ALTCHA handles the human/bot question. PowForge adds the economic layer — so committed users pay sats, not subscriptions.
⚡ The billing wedge
ALTCHA's commercial offering, Sentinel, is a flat monthly subscription priced at €99 to €799 per month and tied to their hosted cloud. PowForge is per-solve sats — you pay only for the friction your traffic actually generates, and you keep everything self-hosted. No vendor lock-in, no minimum spend.
When ALTCHA is the right call
If you just need to weed out dumb bots on a contact form or comment box and you don't care about a payment tier, ALTCHA is excellent. It's well-maintained, GDPR-friendly, and has a strong open-source community. PowForge is the right next step when you want per-action pricing or revenue from bot friction.
Composable — run both
ALTCHA at the edge handles volume cheaply. PowForge on high-value actions (registration, API calls, premium search) adds the Lightning skip tier so legitimate paying users clear in under a second instead of grinding the PoW like a bot would. They complement each other.
Same PoW. Better economics.
Both use SHA-256 in pure JavaScript. The hash itself is not the product — the economics around it are. PowForge prices interaction in sats; ALTCHA Sentinel prices it in subscriptions. Same proof-of-work core, different bill at the end of the month.
Add a Lightning tier to your CAPTCHA
Drop-in npm package. Works alongside ALTCHA. Starts at 3 sats per skip.
npm install @powforge/captcha