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Castle
Protect Product / Field guide
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Castle fraud detection review
Account security and decision APIs. Editorial score: 9.2 out of 10. Best fit for teams securing signup and login flows with API-led decisioning.
By Michael Delgado · Reviewed against the 22-criterion rubric. Product/access source checked 21 October 2026.
9.2
Editorial score / 10
Rank 3 of 20
Castle centers account protection around risk and filter requests. Its free and Pro allowances are denominated in API usage, and alternative IP lookup quantities use the same dollar credit.
##
Where it fits
Best fit for teams securing signup and login flows with API-led decisioning. Our rating weights practical decisions, account linkage, signal depth, implementation and commercial fit. A tenth of a point is a close judgment; use the full
[methodology](/methodology/)
and your own traffic before choosing.
##
Signals, output and workflow
In a proof of concept, request a sample response for a clean user and a suspicious user. Record which fields are available to engineering, risk and support, and whether the result directly supports the action your team needs.
##
Access and pricing
Free access:
1,000 Risk API calls / month, or equivalent IP usage.
Public entry price:
200 US dollars / month including 40,000 Risk and Filter requests. Products in this comparison meter different units. Calculate the number of calls your actual flow will make, confirm included products and any overage, and get the latest terms from the vendor.
##
Strength and trade-off
Strength:
Best fit for teams securing signup and login flows with API-led decisioning.
Trade-off:
Price comparisons need the actual request mix; a Risk request and an IP lookup are different billing units.
##
What to verify in a test
-
Run the product on the same signup, login or payment cohort you use for other candidates.
-
Count known abuse caught, legitimate users flagged, missing responses and latency.
-
Compare the output to the operational action your team can take, then normalize the quote to that event volume.
Next step:
Read the
[parallel test guide](/guides/parallel-fraud-tool-test/)
and the
[alternative shortlist](/alternatives/)
before committing to a plan.
##
Source
[Vendor page ↗](https://castle.io/pricing/)
##
FAQ
###
What is Castle best for?
Best fit for teams securing signup and login flows with API-led decisioning.
###
What does Castle cost?
200 US dollars / month including 40,000 Risk and Filter requests. Free access: 1,000 Risk API calls / month, or equivalent IP usage. Check the current vendor page for plan details and billing units.
###
What should I test before adopting Castle?
Price comparisons need the actual request mix; a Risk request and an IP lookup are different billing units.
[Visit Castle ↗](https://castle.io/pricing/)
Review index
###
Castle
Account security and decision APIs
[How scores work ↗](/methodology/)
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