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

Annotations already declare readOnlyHint=false, idempotentHint=true, and destructiveHint=true, so the agent knows this is an idempotent-but-overwriting mutation. The description adds genuine scope context ('other reminders are unaffected', override of the account default), but given destructiveHint=true it never says whether an existing per-reminder voice config is overwritten or merged, nor any permission requirements. Useful but incomplete against a destructive mutation.

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?

Well front-loaded: the one-line purpose and routing guidance precede the Args block. The scenario examples are illustrative rather than filler. Slightly long, but every element contributes.

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 an idempotent, non-read-only mutation with an output schema, the definition covers purpose, when/when-not, sibling routing, scope of effect, and all five parameters. Return values are handled by the output schema, so nothing an agent needs to call this correctly is missing.

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%, so the description carries the full burden and does: it names the source for reminder_id (list_reminders) and voice_id (list_voices), enumerates personality values, gives BCP-47 examples for language, and specifies a numeric range with semantic interpretation for speaking_rate. This is meaningfully beyond the bare-typed nullable schema.

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 ('Give one reminder its own voice') plus the exact scope ('overriding the account default'). An agent can distinguish it from clear_reminder_voice (removes a per-reminder voice) and set_voice_settings (account-level) without opening any 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?

Gives concrete when-to-use scenarios (medication, workout, foreign-language relative), names the prerequisite tools (list_voices, preview_voice), and explicitly bounds the effect with 'Other reminders are unaffected.' Nothing is left to inference.

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