Choose Alloy when…
Choose Alloy if your work looks like high-value transactions, and if you're comfortable requesting a quote before committing.
- High-value transactions
- Marketplace with seller risk
Not for: Low transaction volume
Fraud & Risk Management
Alloy vs Castle
Alloy is priced on request; Castle is freemium. Alloy: Identity decisioning platform for fintech and banking automating KYC, fraud, and credit underwriting workflows via API. Castle: Castle protects user accounts and transactions from takeover, fraudulent signups and abusive usage with a developer-first API. It offers risk scoring, device fingerprinting, webhooks and policies, and is popular with SaaS companies like Sho. Alloy fits marketplace — in practice, high-value transactions. Castle fits B2B and B2C SaaS protecting logins, signups and workspace abuse with a small risk team. On our rubric Alloy scores 3/5 for developer experience and 2/5 for transparency, while Castle scores 5/5 and 5/5. The honest trade-off: Alloy's main drawback — Low transaction volume; Castle's — Weaker on payment fraud vs PSP-native tools. For Castle: Developer-first API with clear docs and webhooks. Alloy is explicitly not the right pick for low transaction volume. Castle is not aimed at payment-first merchants or bot-heavy retail needing dedicated WAF-layer mitigation. Another Alloy advantage: Marketplace with seller risk.
Quick take
Alloy is for marketplace; Castle is for B2B; decide on pricing model.
Feature comparison
 Alloy | | |
|---|---|---|
| Category | Fraud & Risk Management | Fraud & Risk Management |
| Pricing Model | — | freemium |
| Entry Price | $5 | — |
| Free Tier | No | Yes |
| Billing Complexity | — | — |
| Developer Experience | 3/5 | 5/5 |
| Pricing Transparency | 2/5 | 5/5 |
| Lock-in Level | low | medium |
| Migration Complexity | — | — |
| Data Portability | — | — |
| Enterprise | Available | — |
| GitHub Stars | 3.1k | — |
| License | Apache-2.0 | — |
When to choose which
Choose Castle when…
Choose Castle if your work looks like risk scoring for new user signup abuse prevention, and if you accept tighter coupling in exchange for the managed surface.
- Developer-first API with clear docs and webhooks
- Policies let you codify risk rules without retraining
- Fast integration for SaaS login and signup flows
- Reasonable pricing for mid-market SaaS
Not for: Payment-first merchants or bot-heavy retail needing dedicated WAF-layer mitigation.
Common use cases
Alloy
- High-value transactions
- Marketplace with seller risk
- CNP fraud prevention
Castle
- Risk scoring for new user signup abuse prevention
- Account takeover detection via device fingerprint changes
- SaaS platform abuse policy enforcement via webhooks
- Fraud signal enrichment for Shopify checkout flows
- Adaptive MFA trigger based on real-time risk score
Ready to explore?
Check each tool's dedicated page for deeper reviews, setup notes, and pros/cons.
Frequently asked questions
Is Alloy cheaper than Castle?
Alloy's pricing isn't published in our data, so we can't give a definitive comparison. Castle uses freemium pricing. You'll need to request a Alloy quote to compare directly.
Can I migrate from Alloy to Castle?
Migrating out of Alloy is straightforward — it's rated low lock-in (KYC/fraud rules and data sources proprietary to Alloy platform). The harder question is how deeply you commit to Castle afterward, since it sits at medium lock-in (Proprietary fraud API with webhooks). Plan the forward cost, not just the exit.
Which has better developer experience, Alloy or Castle?
Castle scores higher in our rubric (5/5 vs 3/5 for Alloy). Transparency is 5/5 for Castle and 2/5 for Alloy. DX scores are rubric-based, not benchmarks, so evaluate against your own toolchain.
Is Castle a good alternative to Alloy?
They sit in the same category, so yes — Castle is a plausible alternative for many Alloy use cases. It fits best when B2B and B2C SaaS protecting logins, signups and workspace abuse with a small risk team. Skip it if payment-first merchants or bot-heavy retail needing dedicated WAF-layer mitigation.
Community Discussion
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