Product review
Castle fake account detection review
Castle exposes a Multiple Accounts Per Device signal and account-per-device metrics. Teams can inspect associated users and events, then configure policies that allow, review or deny activity according to their tolerance for legitimate shared devices.
Key facts
- Signal
- Multiple Accounts Per Device flags a device associated with more than one user. Accounts per Device metrics support a different tolerance where shared computers are expected. Source ↗
- Investigation
- Filter the signal, group by device fingerprint and inspect related users and events before deciding that the shared device is unwanted. Source ↗
- Response
- Policies can apply an inline action to registration events. Castle also has ready-made Abuse, ATO and Bot scores; multi-accounting is not limited to a raw identifier. Source ↗
- Access
- Free includes 5 US dollars of monthly API usage, equivalent to 1,000 Risk calls or 5,000 IP lookups. Pro starts at 200 US dollars of monthly API usage, equivalent to 40,000 Risk calls. Source ↗
Strengths
- Dedicated account/device signal and inspectable associated accounts.
- Configurable tolerance for family and shared-workplace devices.
- Public entry plan plus risk scores and event policies.
Limitations
- Configure the policy, event coverage and tolerance that match the application’s legitimate multi-account cases.
- IP lookup and Risk API calls draw different amounts from the shared plan credit.
Who it fits
Developers combining account and device metrics with Abuse, Bot and account-takeover scores in a policy-driven workflow.
Compare the alternatives by signup-protection scope when your team needs a different relationship output or operating model.
What the score means
The editorial score of 8.1 out of 10 places this tool in the published comparison. It reflects product fit under the same 37-criterion, six-category framework used for all ten tools.
The facts above help evaluate account linking, signal breadth, registration decisioning, legitimate-user handling, integration and access. Read every criterion and weight.
How to evaluate it
Use the documented Explore grouping to inspect a repeat-signup device. Compare a family computer and separate people on the same router, then test a review action before a deny policy.
Self-serve evaluation account
The Free plan is an account-based evaluation route with published limits, not an anonymous browser checker.
Open evaluation routeUse the public route to inspect access and output, then validate the product on your own permitted traffic.
Sources and further reading
- Product and detection approach · checked October 21, 2026
- Pricing and access · checked October 21, 2026
- Integration and result documentation · checked October 21, 2026
- Multi-accounting signal and linked-account investigation · checked October 21, 2026
FAQ
Does Castle expose multi-accounting directly?
Yes. Multiple Accounts Per Device is a documented signal, and account-per-device metrics allow an application-specific tolerance.
Does one extra account always need a block?
No. The guide explicitly considers family and workplace devices. Configure investigation and response policy to match permitted account use.
What should I verify in a signup pilot?
Check the protected registration event, its account association, the returned evidence and result timing. Include legitimate shared users and confirm the exact feature and billing scope.
Explore checkers, demos and evaluation routes →