Castle provides developer-focused infrastructure designed to detect and prevent bots, account abuse, and fraud. The platform analyzes user behavior in real-time to generate security signals that help organizations identify and block malicious activity. Their technology serves companies across various sectors including Canva, Rockstar Games, and Atlassian. The company's approach centers on behavioral analysis and real-time detection capabilities that integrate into existing application workflows. Castle positions itself as infrastructure that developers can implement to add a trust layer to their applications, focusing on stopping automated attacks and fraudulent account activity before they impact business operations. Castle operates as a product-led company, emphasizing technical capability over traditional sales approaches. The platform is built to scale through automation and systems rather than manual intervention, allowing a small team to serve enterprise-grade customers. Their infrastructure processes user behavior patterns to distinguish legitimate users from bots and abusive actors. The company was founded through Y Combinator's W16 batch and has raised funding from Index Ventures, First Round Capital, and notable angel investors including executives from Datadog, Okta, Duo Security, Palo Alto Networks, Stripe, and New Relic. Castle describes itself as profitable while maintaining growth, focusing on building reusable systems that compound impact over time rather than scaling through headcount expansion.