A timestamp is inside the cached prefix
PrefixAudit rule dynamic-timestamp · v0.1.0
Why it breaks your cache
Cache hits need a byte-exact prefix match. A rendered date or time makes every request unique, so the cache writes full price and reads never. The single most common cause of a 0% hit rate.
How to fix it
Delete the timestamp from the system prompt, or move it to the END of the final user message where it cannot invalidate the prefix. If the model needs "today", inject it as a trailing user turn.
How common is it?
Detected in 76 of 236 production system prompts (32.2%) across 16 vendors.
Estimated impact
Modelled as invalidating 0% of the cached prefix.
Is your prompt affected?
Paste it and find out. Static analysis, in-browser, nothing leaves the page.
Run the audit →