Set Vapi prompt and voice

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

Annotations already mark destructiveHint=true, so the mutation nature is known. The description adds one useful non-destructive detail: it preserves other model settings and attached tool IDs, which helps an agent understand scope. It does not explicitly warn about overwriting the selected fields, but that is implied by 'update'. Since it adds the preservation nuance without contradicting the destructive hint, a 3 is appropriate.

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?

A single sentence that is front-loaded with the action and resource, then adds a key caveat. No wasted words, perfectly scannable for an agent.

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?

Given 7 parameters, low schema coverage, a destructive annotation, and no output schema, the description is too thin. It lacks parameter-level clarification, does not mention any side effects or limitations (beyond preservation), and provides no guidance on when to prefer this over sibling tools. An agent would struggle to use it correctly without opening the schema or experimenting.

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 only 14% (only clientSlug has a description). The description mentions 'first-message, system-prompt, model, and voice fields' but does not map these to the actual parameter names (firstMessage, systemPrompt, modelName, modelProvider, voiceId, voiceProvider). It also fails to clarify the distinction between modelName/modelProvider and voiceId/voiceProvider. With low schema coverage, the description should compensate but does not.

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 clearly states a specific verb ('Update') and names the affected resources (first-message, system-prompt, model, voice fields). It also includes a distinctive preservation clause ('while preserving the assistant's other model settings and attached tool IDs') that sets it apart from a full overwrite. However, it does not explicitly contrast with any sibling tool like apply_template, so differentiation is implied rather than stated.

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 description gives a clear scenario: you want to update only these fields without touching others. This is an implicit usage condition. But it does not name alternatives (e.g., apply_template) or state when not to use this tool. The guidance is adequate but not explicit enough to confidently route an agent.

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