Exact match, word for word. agent-cache takes everything that defines an LLM request - which model you're calling (gpt-4o, Claude, etc.), the full conversation history (system prompt + user messages + assistant responses), sampling parameters like temperature, and any tool/function definitions the model has access to - serializes it all into a canonical JSON string with sorted keys, and hashes it with SHA-256. That hash is the cache key in Valkey. Same inputs down to the last character = cache hit, anything different = miss.

If you want the 'basically the same question' behavior, that's our other package - @betterdb/semantic-cache. It embeds the prompt as a vector and does similarity search, so 'What is the capital of France?' and 'Capital city of France?' both hit. The trade-off is it needs valkey-search for the vector index, while agent-cache works on completely vanilla Valkey with no modules.

In practice, agent-cache hits its cache less often than semantic-cache would, but when it does hit, you know the result is correct - there's no chance of returning a response for a question that was similar but not actually the same.