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

No annotations exist, and the description carries the full load: it discloses the return value (three audio samples), the cost model (free, 10 a day; then Voice Pack minutes at one per video minute; none on 3D films), and plan quota limits (Premium 1, Ultimate 3). That is exactly the behavioral context an agent needs to set user expectations and avoid surprises.

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?

Purpose is front-loaded in the first clause, and the rest follows a logical order: what it returns, cost, next step, then input modes. It is somewhat dense with pricing and plan details, but each sentence carries actionable information, so no rewrite is warranted.

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 5-parameter, all-optional creation tool with no annotations and no output schema, the description covers what comes back, what happens next, what it costs, and how each of the three input modes works. An agent could invoke this correctly and explain the result to the user without further probing.

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 already 80%, so the schema labels the params, but the description adds real meaning: it explains that presenter is a substitute for description, that story_topic works with story_preset, and gives a concrete example of the speaker-oriented style expected. It adds value beyond the schema without documenting every parameter individually.

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 and resource ('Design a brand-new narrator voice from a written description') and pins the underlying product surface (ElevenLabs Voice Design via Settings > Voice > Design a voice). It is clearly distinguished from save_designed_voice, which is named as the persistence step rather than a competing action.

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?

Explicitly describes the follow-up path ('When the user picks one, save_designed_voice keeps it') and gives the three input modes — free-text description, presenter name, or story_topic + story_preset. It also instructs what to describe ('the SPEAKER... not the recording'), which is rare and useful. It stops short of stating when not to use this tool versus existing voices, so it is not a 5.

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