Monitor

Castle

AI-powered fraud prevention tool that blocks bots and account abuse at the edge and in-app.

castle.io

Verified API available Free tier ~3k monthly visits

Quick facts
What is it	AI-powered fraud prevention tool that blocks bots and account abuse at the edge and in-app.
Pricing	Freemium — from $200/mo
Free tier	Yes
Platform	Web Application
API	Yes
Best for	Preventing credential stuffing attacks on login pages, Detecting and blocking account takeover attempts
Domain registered	2014

Data updated Aug. 1, 2026

What does Castle do?

Castle is a security platform designed to protect web applications from automated attacks and fraudulent user activity. It works by analyzing traffic at the network edge to block threats like credential stuffing before they reach your servers, while also monitoring in-app user behavior through an SDK to detect account takeovers, fake signups, and multi-accounting. This dual-layer approach means signals from both layers work together to improve detection accuracy over time.

The tool provides a comprehensive set of features including behavioral analysis with pre-built and custom signals, highly accurate device fingerprinting, bot detection, and AI-driven risk scoring that evaluates threats for abuse, account takeover, and bot activity. It includes a rules engine for real-time action decisions and email intelligence to spot disposable domains and enumeration patterns. A key advantage is the quick setup; you can connect it to Cloudflare with no code or use your own edge stack, starting in monitoring mode before switching to active blocking.

Castle is built for product and security teams at companies of any size that need to protect user accounts without adding friction for legitimate customers. It's particularly useful for SaaS platforms, fintech apps, e-commerce sites, and any service dealing with user logins or sensitive data, helping them reduce fraud-related costs and maintain user trust.

Monitor Predictions

#account security#ai scoring#bot detection#cybersecurity#device-fingerprinting#fraud prevention#real-time protection

Key features

What makes it stand out

Dual-layer defense analyzes traffic at the edge and monitors in-app user behavior

AI scoring evaluates real-time risk for abuse, account takeover, and bot activity

Rules engine allows custom policies to allow, challenge, or deny actions without code changes

Device fingerprinting identifies browsers and devices with 99.5% accuracy

Email intelligence detects disposable domains and fraudulent email patterns

Who is Castle for?

Who benefits most from this tool

Preventing credential stuffing attacks on login pages

Detecting and blocking account takeover attempts

Stopping fake signups and multi-accounting abuse

Pricing

Free tier available — start without a credit card

Free

1,000 API calls
1 API requests per second
All core features
3 days data retention
3 seats, 1 environment

Pro

$200.0/month

Everything in Free, plus:

100,000 API calls
0.002 additional call price
5 API requests per second
Higher rate limits (5 API requests / second)
7 days data retention
5 seats, 2 environments
Chat & email support

Enterprise

Custom

Everything in Pro, plus:

18 months data retention
Unlimited API requests per second
No rate limits
Up to 18 months data retention
Unlimited seats & environments
Dedicated Slack channel & SLA

Trust & presence

Search presence Top 100k site

Domain Domain registered 2014

Gallery

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