Evaluation
Monitoring and evaluation are usually said together and mean different things. Monitoring asks whether you did what you said. Evaluation asks whether it made a difference.
There is no legal requirement to evaluate. The pressure comes from funders and from good practice, not from statute — which means the standard is proportionate to your size and your funders’ expectations, not fixed.
Start from a theory of change so you know what you are testing. For a small charity, a one-page theory of change plus three indicators is a defensible minimum: see proportionate evaluation.