1037 🟧 Cloudflare

Cloudflare Error 1037: Invalid rewrite rule (failed to evaluate expression)

A rewrite rule’s dynamic expression failed at runtime — for example a function received a value of the wrong type or a missing field.

Seen on: Cloudflare

Meaning

Dynamic expressions referencing fields that aren’t present on some requests, or functions with invalid arguments, fail evaluation for those requests.

Common causes

  • Expression references a field absent in some requests
  • Wrong function arguments/types
  • Regex replacement errors

⚡ Quick fix

  1. Simplify and test the expression
  2. Add conditions so the rule only runs when fields exist
  3. Check rule logs/trace

Detailed fix by platform

Cloudflare

  1. # Use Trace (Account → Trace) to see which rule fails for a sample URL

How to diagnose

  1. Rule — Expression
  2. Request — Which requests fail?

🔧 Still not fixed?

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