Castle Raises $9.2 Million in Series A Funding Led by Index Ventures

Castle's Founders Johan Brissmyr and Sebastian Wallin

Castle announced that it has raised $9.2M in Series A funding from Index Ventures. This round brings the company’s total funding to almost $12M. Shardul Shah, partner at Index Ventures will join the board of directors.

Castle announced that it has raised $9.2M in Series A funding from Index Ventures, with participation from existing investors Y Combinator, First Round, and F-Prime Capital Partners. Angel investors joining the round include Zack Urlocker, former COO at Duo Security, and Olivier Pomel, CEO at Datadog. This round brings the company’s total funding to almost $12M. Shardul Shah, partner at Index Ventures will join the board of directors.

Castle’s mission is to make consumers more secure everywhere. Today, it’s easier than ever to attack a system, and even easier to re-use that same attack over and over again. The company aims to make it easier for developers to build strong account security into online applications. The goal is that by embedding Castle into all online applications, the use of passwords and other cumbersome security measures will be eliminated, so users can have a frictionless experience every time or anywhere they are online.

“We started Castle to provide consumers with a safe, yet enjoyable user experience when they’re online,” said Johan Brissmyr, CEO and co-founder of Castle. “It’s getting increasingly harder and more complex to keep users' online accounts and data safe. The onus is often on the consumer to come up with complex passwords and other security measures. We want to flip that responsibility to businesses and empower every one of them to offer bank-grade account security without compromising user experience.”

The team at Castle is making available best practices employed today only by tech giants like Google, Amazon, and Apple with unlimited resources. These companies rely on identity teams to track security issues in real-time and can detect if a consumer is likely to be on vacation, or whether the login is truly out of the ordinary, and can alert users accordingly. Although these tech giants do a great job, their capabilities aren’t available to other companies.

Castle’s models, driven by end user behavior and feedback, offer a unique and innovative approach, as they’re continuously updated, in real-time, based on how users use apps and reset passwords. Castle’s secret sauce doesn't lie in the use of machine learning per se, but its models are driven by end-user behavior and feedback exclusively. Unlike other solutions, there’s no need for supervision from a security team.

Castle aims to be much more than just another add-on security solution. The founders want to build a company that is a trusted, friendly advisor. “We want to enable companies to make qualified decisions about security,” said Brissmyr. “At every point, we want to help companies reduce friction for their users, so that security is embedded into the overall user experience. To do that, companies need to have a deep understanding of how users react to different security measures. Castle provides that insight.”

“Security is the primary concern on everyone’s mind today and the Castle team has figured out an approachable way to make the online world more secure for everyone,” said Shardul Shah, partner at Index Ventures. “We love the global background of the founding team and their product sensibility. In a short amount of time, they’ve build a strong technology platform and onboarded some great customers because of their accessible, yet disciplined approach. I think they have the opportunity to become one of the most trusted names in security.”

To learn more about Castle and how you can make your customers feel safer online, please visit

About Castle

Castle is a user identity company founded by Johan Brissmyr and Sebastian Wallin based in San Francisco. Castle offers an end-to-end solution for user security and account takeover (ATO) prevention. Developers use Castle's APIs to detect automated credential stuffing attacks and human-powered ATOs, automate the recovery process, and breathe easy with zero false lockouts or support queues. Castle is funded by First Round, Index Ventures and Y Combinator.

In this post: Castle, Shardul Shah

Published — Feb. 12, 2019