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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds a genuine behavioral trait beyond that structure: duplicate names do not error and do not create a second record, they return the existing one, which is effectively name-based idempotency the agent would otherwise have to guess. It does not say anything about which account/library context is written to or what the returned record contains.

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 short sentences, no filler, with the dedup behavior front-loaded immediately after the core action. Nothing is repeated from the title or annotations.

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 single-parameter creation tool with no output schema, the description covers what it does, where it writes, and the one surprising edge case. The remaining gap is the return value's shape: an agent can't tell from the description whether the response includes the equipment id it would need for a follow-up rename_equipment call, only that 'the existing one' is returned.

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?

With one parameter and 0% schema description coverage, the description has to carry the semantics, and it does add one important fact: 'name' is the identity/uniqueness key, so supplying an existing name resolves to that existing record instead of failing. It does not state constraints on the name (length, allowed characters, whether it must be unique only within the trainer's library, or how fuzzy the match is). Partial compensation, so a 3.

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 concrete verb (adds) and resource (a piece of equipment) and pins the destination scope ('their own library'), which distinguishes it from catalog-oriented siblings like list_catalog_categories or search_exercises. It doesn't explicitly name rename_equipment or list_library_equipment as related tools, but the scope wording carries enough signal to pick it out of the sibling list.

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 phrase 'to their own library' implies when to use this rather than a catalog operation, and the duplicate note implies an agent does not need to pre-check existence. However, there is no explicit when-to-use/when-not statement or named alternative (e.g. 'use list_library_equipment first to check, use rename_equipment to change'). Usage is inferable rather than stated.

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