Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, openWorldHint=false and destructiveHint=false, so the safety profile is fully covered without description help. The description adds the scoping trait that results are limited to the trainer's own students and are a live snapshot, but says nothing about result size, ordering, or whether an empty response means 'nobody training'.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

A single twelve-word sentence with no filler, and the discriminating qualifier ('right now') is placed early. It is a sentence fragment rather than a front-loaded verb-first statement, which slightly weakens the opening.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a no-parameter, read-only, closed-world list tool with no output schema, the description conveys the entity, the time window, and the population scope, which is close to sufficient. It could say whether results include per-student detail, but the anatomy of this tool is simple enough that little is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool takes zero parameters, so the schema imposes no explanatory burden and the baseline is 4. The description still contributes by defining the implicit filter (trainer's students, currently in progress) that would otherwise be an unstated default.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The sentence names the exact resource (workout sessions) and its temporal scope ('in progress right now') plus the population ('the trainer's students'), which is specific enough to distinguish it from generic session lists. It stops short of an explicit verb ('list') and never names the near-twin sibling list_recent_sessions, so the right-now vs. recent distinction must be inferred.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

There is no explicit statement of when to call this versus list_recent_sessions, list_student_sessions, or list_students_activity. The 'right now' phrasing hints at a real-time check, but the agent is left to infer the selection condition from a single adjective.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.