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Guide · Security

How to Prevent API Abuse Without Authentication

Public APIs need protection even when you can't require user accounts. Rate limits, IP checks, and API keys can stop abuse.

Anonymous surfaces still need abuse ceilings—rate limits and WAF support Cost and Reliability gates. Primary control: Cost Optimization

Anonymous doesn't mean unlimited

Public forms, free samples, and marketing "try it" endpoints can't always require login—but they still cost money when bots arrive. A landing-page "generate a sample report" button hit Claude behind a soft CAPTCHA; a script farm emptied the Anthropic budget in two days. IP rate limits, a free key after email verify, and a hard daily completion ceiling restored predictable spend.

Friction that works without full AuthN

Cap hard by IP at the edge. Offer a free API key (email verify) so quotas attach to an identity even if it's light. CAPTCHA/hCaptcha on human-facing buttons. WAF rules for datacenter/bot ASNs. Alert on volume spikes the same day, not on invoice day.

Cloudflare rate-limit rules need no app deploy; API Gateway throttling works if AWS is already in front.

Unauthenticated ≠ unprotected

APRF Authentication still expects abuse controls on public surfaces—IP/key ceilings count when full login isn't an option. Auth can come later; unbounded spend can't.

Next: Cost Optimization

Open the related pillar specification for mandatory checks, artifacts, and pass conditions. Self-attest is optional.

View Cost OptimizationSelf-attest

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Frequently asked questions

How do I secure a public API without login?
Use rate limiting by IP, API keys for free tier, CAPTCHA for forms, and WAF rules. Monitor traffic and set billing alerts. Even without auth, you can limit abuse.
What rate limit should I use for public APIs?
Start with 100-500 requests per minute per IP. Adjust based on your cost per request and typical usage. Add stricter limits for free tier API keys.
Can I prevent API abuse without requiring signup?
Yes. IP-based rate limiting, CAPTCHA, and WAF rules work without authentication. For higher limits, require a free API key (email signup).