# Features

Sentinel combines several independent detection mechanisms into one risk decision. You don't need to enable everything — most deployments start with the defaults and add features as their use case requires.

## Core detection

- **[Adaptive Captcha](/docs/sentinel/features/adaptive-captcha/)** — scales what a visitor sees to their risk score, from a frictionless proof-of-work check up to an interactive Code Challenge, instead of a fixed difficulty for everyone.
- **[Human Interaction Signature (HIS)](/docs/sentinel/features/human-interaction-signature/)** — interaction analysis that estimates the probability a request came from a human.
- **[Autopilot](/docs/sentinel/features/autopilot/)** — automatically tunes challenge difficulty and policy based on observed traffic, instead of a static config you set once.
- **[Threat Intelligence](/docs/sentinel/features/threat-intelligence/)** — real-time IP reputation and blocking from open-source and live-traffic sources.

## Content moderation

- **[Classifier](/docs/sentinel/features/classifier/)** — NLP-based spam and content scoring for submitted text.
- **[Phishing Detection](/docs/sentinel/features/phishing-detection/)** — validates URLs in submitted content against known phishing sources.
- **[Similarity & Training Data](/docs/sentinel/features/similarity-training-data/)** — pattern-matching against example datasets you provide, for custom moderation rules.
- **[Email Spam Filter](/docs/sentinel/features/email-spam-filter/)** — spam scoring for inbound email.

## Abuse prevention

- **[Rate Limiters](/docs/sentinel/features/rate-limiters/)** — flexible, multi-layer throttling by IP, key, or custom identifiers.
- **[Detection Signals](/docs/sentinel/features/detection-signals/)** — supporting signals (IP resolution, header entropy, language detection, link/redirect analysis) that feed into the overall risk score.

## Where to start

If you're not sure what to enable first, see [Use Cases](/docs/sentinel/use-cases/user-registration-protection/) for recommended feature combinations by scenario, or just leave Autopilot on and let Sentinel tune itself against your real traffic.