Castle

Castle is a security platform focused on stopping automated and human-driven abuse of user accounts and application actions in real time. It analyzes signals including device fingerprints, IP reputation, network characteristics, and the behavioral patterns of how a user moves through signup, login, and in-app actions, then scores each request and can automatically block, challenge, or allow it based on rules the customer configures. It is used to prevent credential stuffing and account takeover, fake account creation, fake reviews and spam, payment and promotion abuse, and other policy violations, and it provides APIs and a dashboard for investigating incidents and managing responses. Castle emphasizes catching abuse that gets past traditional bot mitigation, including attacks that use real browsers or low-and-slow human fraud, by modeling normal behavior for each application. In 2025 it extended its detection to the network edge through a managed Cloudflare integration, so requests can be scored before reaching a customer's servers. Castle is aimed at web and mobile applications, particularly consumer platforms and marketplaces, that need account protection beyond a basic web application firewall. It offers a free developer tier with limited volume, and paid plans priced by the number of requests or users evaluated.