Does the description explain when to use this tool, when not to, or what alternatives exist?
It provides explicit use context: remember anything worth keeping, with concrete examples (processed items, running list, decision, intermediate results), and motivates persistent storage ('Without it, everything you learn is lost'). It does not explicitly list exclusions or contrast with memory_delete/list, but those are not competing operations for writing a value, so the guidance is sufficient.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.