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

Annotations already declare it is a non-destructive write into an open world, so the credential/safety profile is partly covered. The description adds genuinely useful cost context ('uses none of the plan's voices of its own and spends nothing'), which is the kind of side-effect an agent needs. It still says nothing about idempotency, failure modes, or the effect on existing voices, so it is solid but not rich.

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 sentence carries the purpose, source, and effect, followed by a short sentence on cost; nothing is wasted and the main action is front-loaded. The nested parenthetical does make the first sentence denser than it needs to be.

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 four-parameter mutation with no output schema, the definition covers where the inputs come from, what the result enables, and what it costs in plan resources. Only repeat-invocation behavior and error conditions remain unstated, a minor gap against annotations that already flag it as a non-destructive write.

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 description coverage is 100%, so every parameter is already documented, including the source of owner_id/voice_id and the default naming behavior. The description restates that owner_id and voice_id come from voice_library_search and that name is the selection key, which is helpful but largely duplicative of the schema. Baseline 3 is appropriate.

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?

Names a specific verb and resource ('Keeps a voice from ElevenLabs' library') and scopes it with the exact source fields (voice_library_search's ownerId and voiceId) plus its downstream effect (pickable by name in Create). That is enough to distinguish it from voice_clone, voice_library_search, and voice_remove without opening a 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 establishes the prerequisite flow clearly: values come from voice_library_search, and the kept voice is chosen by name later. It does not explicitly exclude alternatives (for example when to clone with voice_clone instead) or say what happens if the voice is already kept, so it stops short of full when/when-not guidance.

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