Castle

Castle develops a fraud and abuse prevention platform that provides dual-layer defense by running natively at the edge and in-app as one integrated system, with signals flowing between both layers so that early blocking sharpens later detection. The platform offers a complete stack of data, tools, and APIs eliminating the need for multiple disconnected tools, including behavioral analysis (with out-of-the-box signals or custom aggregations and rate limiters for detecting credential stuffing, impossible travel, multi-accounting, and more), device fingerprinting (99.5% accurate, uncovering headless browsers, tampering, and carrier data), bot detection (identifying automated behavior and tampering), AI scoring (self-learning AI for spotting account takeover attempts and abusive behavior), a rules engine (real-time allow, challenge, or deny actions without code changes), email intelligence (assessing email reputation, disposable domains, and enumeration patterns), and case and state management (managing dynamic trust, block, and review lists). Castle provides analytics with up to 18 months of historical data for proactive threat hunting, including pattern exploration, network analysis, session monitoring, and rule backtesting. The platform supports use cases including fake accounts, account takeovers, multi-accounting, content abuse, SMS pumping, account sharing, transaction abuse, and API abuse. Castle differentiates itself through its dual-layer architecture (edge and in-app as one system), its 100ms response time, its pay-as-you-go pricing starting at $0 for 1,000 requests per month, its ability to go live in minutes starting in monitoring mode and switching to blocking, and its comprehensive single-API approach covering device intelligence, bot detection, scoring, IP and proxy analysis, email intelligence, custom metrics, alerts, rule evaluation, and state management. Founded in 2015 and headquartered in San Francisco, United States (with operations in Malmo, Sweden), Castle has raised approximately $13.7 million in a Series A round backed by Index Ventures, Y Combinator, First Round Capital, F-Prime Capital, FCVC, Nordic Makers, SparkLabs Global Ventures, Rising Tide Fund, UpHonest Capital, Page One Ventures, Kindling Capital, Hard Yaka, Walking Ventures, Brainchild, and Eight Roads Ventures.