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

Annotations already declare readOnlyHint=true, openWorldHint=false, and destructiveHint=false, so safety is covered. The description's one piece of added context is 'if any', which tells the agent the result may be absent when the student is not training — a genuinely useful behavioral hint, though the tool's response shape and null-vs-empty semantics remain unspecified.

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?

One short sentence with zero filler, and the qualifying condition ('in progress, if any') is front-loaded where the agent reads it first.

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 one-parameter read with annotations covering safety and no output schema, the description tells the agent what it returns and that it may be absent. Only minor gaps remain, such as what the session object or the no-session case actually looks like.

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?

Schema coverage is 100% and the single parameter studentId is already documented with a cross-reference to list_students. The description adds nothing about the parameter, which is acceptable at this coverage level but contributes no extra value.

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 description names a specific resource and scope: the workout session a student has *in progress*, which distinguishes it from historical-session siblings like list_student_sessions and list_recent_sessions. However, it never differentiates from get_workout_session or list_live_sessions, and it is phrased as a noun fragment rather than a verb+resource statement.

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 guidance on when to use this tool versus the many adjacent session-retrieval siblings (get_workout_session, list_live_sessions, list_student_sessions, get_session_events). The 'in progress' framing implies a use case, but the agent must infer it.

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