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

Annotations already declare readOnlyHint=false and destructiveHint=false, so the description doesn't need to re-establish safety. It adds real behavioral context beyond that: the workout is not placed on the calendar, it produces a library card the athlete applies, and it persists even if later removed from the calendar. It doesn't address auth/permissions or how duplicates/overwrites are handled.

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?

Front-loaded with the core action and the calendar exclusion, and the body is dense with actionable detail. Slightly long, with plan_workouts referenced twice and a mildly tangled final sentence, but almost nothing is filler.

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?

No output schema exists, and the description compensates by describing what is produced (a library card) and how it can later be scheduled via plan_workouts + workoutId. For a two-parameter write tool this is close to sufficient; only error/overwrite behavior is unstated.

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%, so baseline would be 3, but the description adds genuine meaning: the workout object is 'the same object as plan_workouts' custom items[].workout', and notes are 'the workout's own notes: intent, cues'. It also explains the read-then-resubmit pattern for copying, which the schema alone cannot convey.

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 states a specific verb and resource ('Save a workout to the athlete's library') and immediately contrasts it with the sibling plan_workouts by scope ('WITHOUT putting it on the calendar'). An agent can distinguish this from plan_workouts without opening either schema.

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?

It gives explicit when-to-use cases ('a variation of a session for later, a template they asked to keep'), an explicit exclusion with routing ('For a session on a day use plan_workouts'), and even a workflow for the copy-with-a-change case. Alternatives are named rather than implied.

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