URL Filter — Notes

Functional

• Check URLs against threat lists.
• Push updates of bad-list deltas to clients.
• Aggregate user reports.

Non-functional

• Sub-ms client-side lookup.
• Privacy-preserving server queries.
• 99.99% availability for updates.

Trade-offs

• Client list cache vs server-only lookup: cache saves latency + privacy.
• Hash prefix preserves privacy; full URL not sent in steady state.

Refs

• Google Safe Browsing v4 spec.
• Microsoft SmartScreen, PhishTank.
• ByteByteGo "Design web safe browsing".