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Product17 January 2025·3 min read

How Paycux Radar does rate limiting with device fingerprinting

Shipping is the easy half.

Paycux engineering

Shipping is the easy half. The hard half is deciding what the thing is supposed to do for someone who has never read your roadmap and does not care about your architecture.

This piece walks through how we think about it at Paycux, what we have changed our minds about, and where the sharp edges are.

The problem with traditional rate-limiting

That brings us to the problem with traditional rate-limiting. Defaults are the product. Most people will never open the settings screen, which means the behaviour you chose for them is the behaviour they will experience forever.

Defaults are the product. Most people will never open the settings screen, which means the behaviour you chose for them is the behaviour they will experience forever.

Device Fingerprinting: Radar’s key to intelligent rate-limiting

Device Fingerprinting: Radar’s key to intelligent rate-limiting is where this gets concrete. Naming is design work. If the team argues about what to call something, the disagreement is usually about what it is, and shipping before that is settled means shipping the confusion to customers.

Ship the smallest version that is honest about its limits. A feature that does one thing completely beats one that does five things with an asterisk on each.

  • Choose defaults as carefully as features
  • Settle the name before you ship the thing
  • Ship the smallest honest version
  • Say plainly what the feature does not do

Progressive rate-limiting

Progressive rate-limiting deserves its own treatment. Defaults are the product. Most people will never open the settings screen, which means the behaviour you chose for them is the behaviour they will experience forever.

Defaults are the product. Most people will never open the settings screen, which means the behaviour you chose for them is the behaviour they will experience forever.

The difference between brute force and normal use

That brings us to the difference between brute force and normal use. Naming is design work. If the team argues about what to call something, the disagreement is usually about what it is, and shipping before that is settled means shipping the confusion to customers.

Ship the smallest version that is honest about its limits. A feature that does one thing completely beats one that does five things with an asterisk on each.

Ship the smallest version that is honest about its limits.

Keeping services available during attacks

Consider keeping services available during attacks. Defaults are the product. Most people will never open the settings screen, which means the behaviour you chose for them is the behaviour they will experience forever.

Defaults are the product. Most people will never open the settings screen, which means the behaviour you chose for them is the behaviour they will experience forever.

Real-time detection and response

That brings us to real-time detection and response. Defaults are the product. Most people will never open the settings screen, which means the behaviour you chose for them is the behaviour they will experience forever.

Defaults are the product. Most people will never open the settings screen, which means the behaviour you chose for them is the behaviour they will experience forever.

Beyond simple blocking: handling attempts according to your needs

That brings us to beyond simple blocking: handling attempts according to your needs. Naming is design work. If the team argues about what to call something, the disagreement is usually about what it is, and shipping before that is settled means shipping the confusion to customers.

Ship the smallest version that is honest about its limits. A feature that does one thing completely beats one that does five things with an asterisk on each.

Where this leaves us

None of this is exotic. It is the ordinary discipline of deciding what you own, writing down what you assume, and making the failures loud enough to notice.

If you are working through the same problem and want to compare notes, the docs cover the mechanics and the console shows the behaviour on your own data.

Everything here, already built

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