Castle

Castle is a fraud prevention and account security platform founded in 2015 by Johan Brissmyr (CEO) and Sebastian Wallin (CTO). Originating from the founders' vision as two engineers in Sweden, the company aims to shift the responsibility of security from end-users to online businesses. Castle participated in the Y Combinator Winter 2016 batch and is headquartered in San Francisco.

The company provides a developer-focused infrastructure designed to stop bots, account abuse, and fraud. Castle's business model is delivered as a Software-as-a-Service (SaaS) platform, primarily serving B2B companies that need to secure their web and mobile applications from activities like credential stuffing, fake signups, and transaction fraud. Revenue is generated through a pay-as-you-go subscription model based on API call volume or, for enterprise clients, monthly tracked users (MTU). The company offers a tiered pricing structure, including a free plan for low-volume usage, a pro plan, and a custom enterprise plan.

The platform operates through a dual-layer defense system, combining analysis at the edge with in-app monitoring via an SDK. Key features include advanced device fingerprinting, behavioral analysis, bot detection, AI-powered risk scoring, and email intelligence. This technology allows businesses to distinguish between legitimate users and malicious actors in real-time by analyzing signals such as device integrity, IP reputation, and user behavior patterns. The system enables automated responses, such as blocking or challenging suspicious activities, without negatively impacting the experience for genuine users.

Keywords: fraud prevention, account security, bot detection, account takeover, real-time security, cybersecurity, behavioral analysis, device fingerprinting, API security, SaaS, user authentication, credential stuffing, multi-factor authentication, risk scoring, transaction fraud, spam prevention, identity verification, developer APIs, edge computing security, machine learning