Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description must carry the burden. It states 'calculate Euclidean distance' which is straightforward. It doesn't elaborate on output, performance, or edge cases, but the existence of an output schema reduces the gap. Adequate for a simple mathematical tool.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.