Sentinel vs Castle
Castle (castle.io) is a bot-detection and account-abuse platform focused on account takeover and signup fraud, with a strong reputation in marketplaces and SaaS. Castle scores user actions; Sentinel evaluates the device and network beneath them. Both are useful, but they catch different threats.
Weighing device intelligence tools more broadly? See our guide to the best Fingerprint alternatives in 2026.
Sentinel vs Castle — Side by Side
| Feature | Sentinel | Castle |
|---|---|---|
| Response Latency | < 40ms | ~100ms (vendor-stated) |
| Residential Proxy Detection | ✓ Full | Partial (list-based signal) |
| Antidetect Browser Detection | ✓ Full | Limited |
| Behavioral / Session Analysis | Device + network | ✓ Session anomaly + policies |
| Account-Graph Linking | Device clustering | ✓ Full |
| No-Code Policy Editor | Code-first API | ✓ Yes |
| Free Tier (no credit card) | ✓ 1,000 req/hr unlimited | ✓ 1,000 req/mo free |
| Self-Serve Signup | ✓ Yes | ✓ Yes (enterprise via sales) |
| Pricing Transparency | ✓ Public | ✓ Public |
What is Castle?
Castle is a bot-detection and account-abuse platform built around device fingerprinting — session anomalies, device-graph linking, and risk policies you author. Founded in 2015, it is widely deployed at marketplaces, SaaS platforms, and creator economy products.
- Device fingerprinting engine (vendor-stated 99.5% accuracy)
- Strong policy editor for risk rules
- Account-graph and device-linking analytics
- Webhook-driven challenge flows (CAPTCHA, MFA, manual review)
- Native SDKs for iOS, Android, and web
- Per-event pricing scales fast at higher volumes
- Residential-proxy detection (residential_proxy_access) relies on recently observed provider IP lists rather than live network-layer analysis
- No documented signal specifically for commercial antidetect browsers (Kameleo, GoLogin, AdsPower) — coverage is indirect, via spoofed-device and headless-browser signals
- Enterprise pricing (from ~$4,000/month) is sales-negotiated
- Complex policy editor — initial config takes engineering time
Free tier: 1,000 requests/hour. No card, no expiry. Growth at €49/mo (founding price); enterprise by agreement.
Castle publishes its pricing: a free tier of 1,000 API calls/month, a Pro plan at $200/month for the first 100,000 calls (then $0.002 per call), and enterprise plans starting around $4,000/month.
When to use Castle, when to use Sentinel
- Your fraud problem is account-graph clustering across known users and you have engineering time to maintain a custom risk policy.
- Your attackers use residential proxies and antidetect browsers (Castle has limited visibility here)
- You need detection in under 40ms server-side with no policy editor to maintain
- You want to start free with no credit card or sales call
- You want the network + device layer signals Castle does not surface
Get started with Sentinel — free
1,000 API requests per hour. No credit card. No sales call. Detects what Castle misses.
Frequently Asked Questions
Is Sentinel a replacement for Castle?
They overlap partially. Castle excels at device fingerprinting and policy-driven account-takeover detection. Sentinel excels at network and device-layer fraud — residential proxies, antidetect browsers, AI bots — that Castle does not cover at the network layer. For most teams, the right answer is: use one or both depending on threat model. They’re complementary more than competitive.
What does Castle miss that Sentinel catches?
Sentinel catches residential proxy networks (commercial and peer-to-peer residential networks), antidetect browsers (Kameleo, GoLogin, AdsPower, Dolphin Anty), and AI-driven agentic bots — three vectors where Castle relies on its behavioral layer to indirectly flag the resulting account behavior, often after damage is done. Sentinel flags them at the request that creates the account, before the policy engine ever has to fire.
Does Sentinel offer policy-driven account flows like Castle?
Sentinel returns a structured verdict (allow / review / block) plus the underlying signals; you implement your own policy in your application code. Castle ships a hosted policy editor. If you want a turnkey policy product, Castle is stronger here. If you want raw signals to compose into your own logic, Sentinel is faster to integrate.
Is there a free Castle alternative?
Yes. Sentinel’s free tier provides 1,000 API requests per hour with no credit card and no expiry. Castle also offers a free tier of 1,000 API calls per month; its paid Pro plan starts at $200/month.