How to Detect API Abuse

API abuse rarely starts with a clear “attack.” It usually looks like normal traffic that slowly becomes expensive, slow, or dangerous.

This guide lists practical signals teams use in production to detect abuse early.

1. One API key from many IPs

This is the most common signal of leakage or client-side embedding.

• Track unique IPs per key (daily + weekly).
• Flag sustained growth, not one-off spikes.
• Correlate with request volume.

2. Sudden traffic growth from a single customer

Indicators:

• 2–5× increase within 24–72 hours
• No corresponding business explanation
• Repeated endpoint patterns

3. High request rate with low variance

Bots are consistent. Humans are not.

• Identical intervals (e.g., every 200ms)
• Same endpoints in loops
• Low entropy in paths and parameters

4. Geographic anomalies

• Traffic jumps to new countries overnight
• Impossible travel (EU → Asia → US in minutes)
• Cheap hosting ASN clusters

5. Error-driven probing

• High 401 / 403 / 404 rates
• Endpoint enumeration patterns
• Sequential IDs

Simple detection checklist

1. Unique IPs per key
2. Requests per minute per key
3. Top endpoints per customer
4. Error rate per IP/key
5. Country + ASN distribution

What to do when you detect abuse

1. Confirm ownership
2. Rotate key
3. Throttle temporarily
4. Notify customer
5. Investigate leak source

Why teams miss this

• Only total traffic is monitored
• No per-key baselines
• No IP history
• No alerting on growth rate

Abuse is cheapest to fix when it’s small. Detection is the real control.