A team caches their tool definitions in the prompt. They add a new too — CCA Advanced Practice — Claude Cert Academy

A team caches their tool definitions in the prompt. They add a new tool by appending to the tools array. What happens to the cache?

• Cache hits continue normally — adding to the array preserves the cache key
• Cache is invalidated — the prefix has changed, so the next call is a cache write
• Cache hits work for the original tools and miss only for the new tool
• Cache is partially invalidated by tool count only

Answer: Cache is invalidated — the prefix has changed, so the next call is a cache write

The cache key is the literal bytes of the prompt prefix. Adding a tool to the array changes the bytes of the cached region, so the cache is invalidated entirely. The next call writes a new cache entry. Adding tools is unavoidable when the toolset grows; the mitigation is to cache only the stable subset.

Continue to Claude Cert Academy