Castle
YC W16San Francisco, US · Founded 2015 · 20 employees · Hiring · 8 known investors
Find your way into Castle
320 people in our graph share verified history with the Castle team — schools, employers, funds. One of them is your warm intro.
Akshat Goenkaunlockedknows Sebastian Wallin · together at Y Combinator (overlapped)
×9knows the team · via Y Combinator
×2knows the team · via The Faculty of Engineering at Lund University
Castle builds trust infrastructure for the modern internet, helping organizations detect and prevent fraud and account takeover attacks. The company serves enterprise and mid-market customers requiring security and identity verification solutions.
Also known as Castle Intelligence · Castle.io
CybersecurityDeveloper ToolsEnterprise SoftwareSaaSSecurityFraud DetectionUnited States of AmericaAmerica / CanadaFully Remote
Founders & leadership· Y Combinator alumni (W16)
Castle was founded in 2015 by Johan Brissmyr and Sebastian Wallin.
JB
Johan BrissmyrinCEO & Co-founder
SW
Sebastian WallininCo-FounderSebastian Wallin is founder and CTO of Castle, which builds fraud detection and account takeover prevention infrastructure for enterprise customers.
Board
SS
Shardul Shahin𝕏Investor at Index Ventures
Investors · 8
Index Ventures✓ verifiedSan Francisco · $540K – $10.8M
Y Combinator✓ verifiedSan Francisco · $500K
First Round Capital✓ verifiedSan Francisco · $1M – $7M
F-Prime CapitalCambridge · $3M – $10M
Walking VenturesLondon · $650K – $1.3M
Boost VCreportedSan Mateo · $500K
SparkLabs Global VenturesreportedPalo Alto
Winklevoss CapitalreportedNew York · $100K – $5M
Founder mafia
2 people who came through Castle went on to found or lead other companies.
Competitors · 8
by search overlap
Fingerprint82 shared keywordsFingerprint provides device identification and fraud detection services for online businesses, leveraging browser fingerprinting technology to identify devices and prevent fraud and bot activity.
Cloudflare Turnstile76 shared keywordsCloudflare provides a global cloud network platform delivering security, performance, and development services through sixty-plus integrated services including SASE, application security, and full-stack development infrastructure.
Firefox,58 shared keywordsMozilla is a global community organization that develops and maintains open-source internet infrastructure, including the Firefox web browser and Thunderbird email client, while advocating for internet openness, privacy, and user control. The organization also invests in responsible technology startups and creates open-source AI tools for developers.
InterPositive57 shared keywordsNetflix operates a subscription streaming service for films and television, producing original programming alongside licensed content for members worldwide.
Zenrows55 shared keywordsZenRows Extract is a web scraping tool that converts supported websites into typed JSON without requiring custom parsers or CSS selectors, reading a page's DOM to automatically detect and return fields such as prices, ratings, contacts, and listings. It maintains prebuilt extractors for specific sites (e.g. e-commerce, travel, real estate, and professional profiles) and offers a css_extractor option for unsupported pages.
Human Security55 shared keywordsHUMAN is a cybersecurity company focused on detecting and stopping automated bot attacks and digital fraud. This page presents its leadership and culture, describing the organization as mission-driven.
Netezza54 shared keywordsIBM is a global technology company whose business spans enterprise software (including Red Hat, HashiCorp, and Confluent), IT infrastructure such as mainframes, servers, and storage, and IT consulting services. The company is also investing heavily in quantum computing and AI-based enterprise offerings, including its Lightwell open-source software security clearinghouse and the Anderon quantum wafer foundry.
Dataxu54 shared keywords
Companies competing with Castle for the same Google search keywords, organic and paid, via search-intersection analysis.
In the news
Less Money More Problems: The Castle Chronicleresearch.castlelabs.io · Jul 2026Frequently asked questions
- What does Castle do?
- Castle builds trust infrastructure for the modern internet, helping organizations detect and prevent fraud and account takeover attacks. The company serves enterprise and mid-market customers requiring security and identity verification solutions.
- Who founded Castle?
- Castle was founded by Johan Brissmyr, Sebastian Wallin in 2015.
- Who are Castle's investors?
- Castle's investors include Index Ventures, Y Combinator, First Round Capital, F-Prime Capital, Walking Ventures, Boost VC, SparkLabs Global Ventures, Winklevoss Capital.
- Where is Castle headquartered?
- Castle is headquartered in San Francisco, US.