Sentinel vs Castle
Castle (castle.io) is a behavioral biometrics 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.
Sentinel vs Castle — Side by Side
| Feature | Sentinel | Castle |
|---|---|---|
| Response Latency | < 40ms | ~80–150ms |
| Residential Proxy Detection | ✓ Full | Partial (IP-graph only) |
| Antidetect Browser Detection | ✓ Full | Limited |
| Behavioral Biometrics | Device + network | ✓ Mature engine |
| Account-Graph Linking | Device clustering | ✓ Full |
| No-Code Policy Editor | Code-first API | ✓ Yes |
| Free Tier (no credit card) | ✓ 1,000 req/hr unlimited | ✗ Trial only |
| Self-Serve Signup | ✓ Yes | Paid tiers via sales |
| Pricing Transparency | ✓ Public | Partial |
What is Castle?
Castle is an account abuse and signup-fraud detection platform built around behavioral biometrics — keystroke timing, 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.
Castle Strengths
- Mature behavioral biometrics engine
- 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
Castle Weaknesses
- Per-event pricing scales fast at higher volumes
- No detection for residential proxy networks at the network layer
- Antidetect browsers (Kameleo, GoLogin, AdsPower) frequently slip through unless paired with another tool
- Signup typically requires a sales call for paid tiers
- Complex policy editor — initial config takes engineering time
Pricing
Castle’s public pricing starts around $99/month for low-volume teams; production volumes typically negotiate custom contracts in the $1k–$10k+/month range. Free trial requires sign-up.
When to use Castle, when to use Sentinel
Use Castle if...
- Your fraud problem is account-graph clustering across known users and you have engineering time to maintain a custom risk policy.
Use Sentinel if...
- Your attackers use residential proxies and antidetect browsers (Castle has limited visibility here)
- You need detection in under 40ms 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 behavioral biometrics 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 (BrightData, ShadowNode, IPRoyal), 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’s free trial requires signup and converts to paid tiers (starting around $99/month).