Castle blog · May 2026
Released an open-source disposable phone number list and described it as a fraud-intelligence resource for fake signups, multi-accounting, referral abuse, and SMS verification abuse.
Company research
Public company, workplace, funding, and market signals
Updated Jul 30, 2026
Overview
Castle (castle.io) is a Brooklyn-based, privately held developer platform for bot detection, fraud prevention, and account security. It sells APIs and SDKs that combine behavioral analysis, device fingerprinting, and risk scoring to stop fake signups, account takeovers, multi-accounting, transaction abuse, and similar threats in real time.
Primary product
Developer-grade fraud prevention and bot detection APIs/SDKs
Founded
2015
Headquarters
Brooklyn, New York, United States
Team size
11-50
Industry
Software Development
Sub-industry
Fraud prevention and account security software
Offices
Brooklyn, New York, United States (HQ)
New York, New York, United States
San Francisco, California, United States
Malmö, Sweden (historical office mentioned by the company)
Kraków, Poland (historical office mentioned by the company)
Business model
usage-based SaaS
self-serve freemium
enterprise subscription
API/SDK platform
Funding
People & investors
Leadership
CEO & Co-founder
Co-founder & CTO
COO
Head of Research
Head of Product & Engineering
Work & culture
Small, profitable, product-led, and technically intense; emphasizes founder-like ownership, direct leadership involvement, fast feedback, and hiring for real-world problem solving rather than résumé polish.
Compensation
The company says compensation is top of market and combines base pay with equity; its hiring post says the compensation ladder is continuously updated using market data.
Product & market
Pricing
Usage-based pricing (requests or MTU) with a free tier and enterprise plans
Differentiators
- —Dual-layer defense across edge and in-app
- —Behavioral analysis instead of CAPTCHAs/puzzles
- —5-minute integration claims
- —Up to 18 months of historical data retention/analysis
- —No-code Cloudflare integration
- —Self-serve start with free tier
- —Developer-first APIs and SDKs
- —AI-based flow classification and real-time risk scoring
Technology
Cloudflare Workers
browser SDK
mobile SDK
Filter API
Risk API
Ruby
PHP
JavaScript
Python
Java
device fingerprinting
behavioral analysis
email intelligence
Customers
Atlassian
Canva
DailyPay
Framer
GitBook
GoTo
Housecall Pro
Novo
Rent the Runway
Rockstar Games
Sinch
YNAB
Competitors
Sift
DataDome
Fingerprint
SEON
Arkose Labs
Kount
ThreatMetrix
IPQS
Scale & contact
Estimated revenue
$1M-$10M (third-party estimate; public snippets also suggest about $4M annual revenue)
Estimated monthly visits
47.6K
Traffic estimate as of Jul 2026
Latest news
Castle blog · Mar 2026
Introduced Castle’s research team and its focus areas, including fingerprinting, automation analysis, mobile security, and software protection.
Castle blog · Jul 2025
Explains Castle’s hiring philosophy, small-team operating model, direct leadership outreach, and top-of-market compensation approach.
Castle blog · May 2025
Launched a no-code Cloudflare integration that extends Castle’s behavioral detection to the edge while keeping the same unified scoring and policy engine as the in-app product.
Castle blog · Feb 2025
Castle announced Antoine Vastel as its new Head of Research, highlighting his background in bot detection, fingerprinting, and adversarial detection.
Jobs and careers at Castle
2 jobs at Castle
Backend Software Engineer
Remote
Engineering & Product
Harvard Square
1y ago
Remote
Full-time
Software Engineer
Remote
Engineering & Product
Harvard Square
2y ago
Remote
Full-time