Castle alternatives
Six alternatives to Castle (castle.io) for account abuse, bots, and fraud, compared on pricing, setup effort, and what each leaves you to build.
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The short version
Updated August 2026
- Teams outgrow Castle for two reasons: the setup asks a lot (backend payloads on every event, step-up flows you build, setup help reserved for Enterprise), and defining and tuning the risks well takes time most teams don't have.
- Rupt is our own product and it's listed first, so read the entries with that in mind. Every claim below is sourced from public pricing pages and reviews.
- The list covers the whole spread: a full fraud engine, a pure identification specialist, two auth-platform add-ons, a digital footprint platform, and an enterprise ML suite.
Why teams go looking.
Castle earned its developer following honestly. A free tier with a $5 usage credit, published unit prices, and docs technical enough to include an account sharing tutorial. In a category where most vendors hide pricing behind a demo call, that counts for a lot.
The thing we hear most from customers is capacity. Most teams don't want to spend weeks defining risks, wiring payloads, and tuning policies; they want help and guidance from people who fight fraud all day, with the option to tweak as they see fit. Castle sits on the other end of that trade: the client SDK issues request tokens, your backend assembles the Risk API payload on every protected event, the step-up flow a verdict triggers is yours to build, and dedicated setup and integration support is Enterprise-only per its own pricing FAQ.
Pricing shape matters too. Pro is $200 a month, Enterprise starts at $4,000 a month, and Vendr's contract data puts the median Castle buyer at $119,500 a year. Between $200 a month and there, nothing exists.
The alternatives.
Pricing pulled from public pages, August 2026. Where a vendor hides pricing, we cite third-party contract data and say so.
1. Rupt That's us
A full fraud engine built around your product. One evaluation returns the fingerprint, 100+ identification signals, scored risks, and an allow / challenge / block / add-to-list verdict. Rupt hosts the challenge if one is needed.
Focus:Product-level fraud and abuse: detection, rules, and enforcement in one engine.
Pricing:$99/month with 20,000 evaluations included, then $0.005 each, and the price goes down with volume. Challenges $0.10 only when delivered.
Strengths
- +Rules engine and challenge engine included in the base plan.
- +AI agent monitors new patterns and investigates cases marked for manual review.
- +People detection estimates how many humans share an account rather than how many browsers appear on it.
- +Cross-browser device linking, plus email, IP, and phone intelligence in the same call.
- +Unified user view for AI agents and humans to make informed decisions.
Keep in mind
- -Fewer client SDK platforms than Castle (no Flutter today).
- -Fast-paced startup; the product evolves quickly.
2. Fingerprint
The identification specialist: a browser-scoped visitor ID with a claimed 99.5% accuracy plus 20+ Smart Signals that you feed into decisioning you build yourself.
Focus:Raw device identification: a browser-scoped visitor ID and signals, with decisioning left to you.
Pricing:$99/month for 20,000 API calls, then $4 per 1,000. Free tier of 1,000 calls a month. Enterprise is custom.
Strengths
- +Best-in-class identification accuracy and the broadest SDK matrix, 11 client platforms.
- +Excellent docs and developer experience.
- +First-party CDN serving on Enterprise so ad blockers don't eat the script.
Keep in mind
- -No rules engine, challenges, or decisioning; signals in, everything else is yours.
- -On G2, expensive is the most-mentioned con.
- -No account-level risks like sharing or concurrency; the unit is the visitor, not the account.
3. Stytch Device Fingerprinting
Device fingerprinting and bot protection sold as an add-on to the Stytch auth platform, with deterministic verdicts on login and signup traffic.
Focus:Device fingerprinting as an add-on inside the Stytch auth platform.
Pricing:Advertises 10,000 free fingerprint lookups per month, then $0.005 per lookup, but requires contacting sales and a minimum commitment of 200,000 lookups a month.
Strengths
- +Tight integration with Stytch auth flows.
- +Simple, deterministic allow / block / challenge responses.
Keep in mind
- -Scope is the auth funnel; no email or phone intelligence, no account sharing or other risks detection.
- -Its own comparison pages omit pricing, so model the total cost yourself.
- -Less useful if you're not otherwise on Stytch.
4. WorkOS Radar
Bot, brute force, and abusive signup detection that rides on WorkOS AuthKit, priced per check.
Focus:Per-check bot and signup abuse detection riding on WorkOS AuthKit.
Pricing:First 1,000 checks free, then $0.002 per check ($100/month per 50,000). Enterprise plans add SLAs.
Strengths
- +Cheapest per check on this list.
- +Effectively drop-in if AuthKit already handles your auth.
- +Covers bots, brute force, impossible travel, and repeat signups out of the box.
Keep in mind
- -The standalone API for non-WorkOS auth stacks is in preview, contact required.
- -Scope is signup and login only; no payment, sharing, or in-product abuse coverage.
- -Some rules are fixed, like a hard three-use limit per email on repeat signups.
5. SEON
A payment fraud platform: digital footprint enrichment on emails and phones, ML scoring trained on historical transactions, and AML screening. Transactions run through the whole product.
Focus:Payment fraud and identity context from digital footprints.
Pricing:Starter at $699/month for 2,500 API calls, about $0.28 each. Premium is quote-based.
Strengths
- +Strong focus and data around risky transaction/payment activity.
- +AML screening in the same platform.
Keep in mind
- -Transaction-shaped API with fixed verdicts; the ML improves through a separate Label API you wire up.
- -Its docs put the lowest supported lookup timeout at 1.5 seconds.
- -Non-payment abuse means molding your events into a transaction shape, then building enforcement yourself.
6. Sift
Enterprise machine learning fraud suite covering payment fraud, account defense, and content abuse, trained on a large cross-customer network.
Focus:Enterprise ML decisioning for payment fraud and trust and safety operations.
Pricing:Quote-based only. Vendr's data shows a median contract of $150,000/year, ranging from about $30,000 to $600,000.
Strengths
- +Mature ML models with network effects across a big customer base.
- +If you have teams already manually reviewing, it integrates into their workflow.
- +Covers payments and chargebacks as first class.
Keep in mind
- -No public pricing; the median contract is six figures.
- -G2 reviewers report false positives creating review workload.
- -Heavy integration relative to the tools above.
- -Focuses on payment/transaction risks, so hard to customize beyond that.
Rupt vs Castle, quickly.
The short version. The full comparison covers signals, migration, and where Castle wins.
Frequently asked questions.
Why choose Rupt.
A full fraud engine, end to end
Identification, intelligence, decisioning, and enforcement are one product, not four you wire together. One evaluation returns the fingerprint, the signals, the scored risks, and a verdict, and Rupt acts on that verdict. Nothing in the middle is left for you to build and then maintain.
100ms at p99
Not an average that hides a long tail. 99 out of 100 evaluations come back inside 100ms, which is what lets you put Rupt directly in the login and signup path instead of running it after the fact.
Risks you can actually build
Rupt ships with its own risks ready to go, and you can compose your own from individual indicators with your own weights and your own actions. That is real customization, not tuning a threshold on somebody else's score.
Unmatched support
Integration setup help, developer meetings, and direct Slack and email access, with replies in hours, on every plan. Most vendors reserve that for their top tier. Don't take our word for it though, just ask our customers.
State of the art AI
The agent protects and detects. It watches your traffic for new and emerging fraud patterns as they form, then tells you what it found and what to do about it, down to the policy changes and updates it recommends you make.
A challenge engine that's a whole journey
Not a single screen bolted onto a verdict. Challenges are customizable and built around an end goal, whether that's adding friction, converting a sharer into their own account, or stopping a takeover, with cooldowns and velocity controls shaping how and when someone gets challenged.
Single-vendor pricing
Fingerprinting, email and phone intelligence, rules, and challenges usually mean a vendor and an invoice each. Because Rupt ships them together, the bundle costs less than the sum of the point tools.
See Rupt on your traffic.
Book a demo and we'll walk through your use case, show you the signals on real evaluations, and price out your volume.
- A walkthrough tailored to your use case.
- How detection, the rules engine, and challenges fit your stack.
- Pricing and a rollout plan for your volume.