Core concepts
Logs
Logs contain the inputs and outputs of each time a Prompt, Tool or Evaluator is called.
All Prompts, Tools and Evaluators produce Logs. A Log contains the inputs
and the output
s and tracks which version of Prompt/Tool/Evaluator was used.
For the example of a Prompt above, the Log would have one input
called ‘topic’ and the output
will be the completion.
![A Log which contains an input query](https://fdr-prod-docs-files-public.s3.amazonaws.com/https://humanloop.docs.buildwithfern.com/docs/2024-07-19T19:46:40.702Z/assets/images/log-drawer.png)