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

The description adds two facts not present in the annotations: writes go to the trainer's own library (ownership scope), and a duplicate name returns the existing record rather than erroring. That dedupe behavior is genuinely non-obvious and useful for an agent. It doesn't cover validation errors or response shape, so not a 5.

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?

Two tight sentences with no filler; the action and scope are front-loaded and the duplicate-name rule follows immediately.

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 write tool with no output schema, the return contract matters, and the description only implies the return (the existing record on collision) without saying what a successful create returns. Annotations cover the safety profile, so this is the main remaining gap.

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 0% for the single 'name' parameter, so the description has to compensate. 'If the name is taken' does convey that the name is a unique key and that collisions are deduped, which is real added meaning, but nothing is said about format, trimming, or naming constraints.

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?

States a specific verb ('Adds') and resource ('a muscle group') plus scope ('the trainer's own library'), which separates it from rename_muscle_group, list_muscle_groups and list_library_muscles. It stops short of naming a sibling tool explicitly, so it lands just below the top tier.

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?

The create intent is clear from 'Adds', and the duplicate-name behavior hints at when calling it is safe, but there is no explicit statement of when to prefer this over rename_muscle_group or list_muscle_groups. Usage is only implied.

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