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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description adds real behavioral value beyond that: pagination via nextCursor and the supportsDirectToolExecution gating rule that determines whether a returned voice is usable by text_to_speech.

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 sentences with zero filler, front-loaded with the returned resource and fields before the usage instruction. Every clause carries information an agent needs.

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?

An output schema exists, so enumerating return fields is partly redundant, but the mention of supportsDirectToolExecution supplies the one cross-tool decision rule the schema cannot. Pagination and filtering are fully covered, leaving no functional gap for a four-parameter, zero-required list tool.

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 the schema already documents limit, query, cursor and includeDeprecatedVoices. The description only echoes cursor (as nextCursor) and deprecation status without adding syntax, defaults, or filter semantics beyond the schema. Baseline 3 applies.

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 ('Return a page of') and resource ('narration voices'), then enumerates the returned fields. No sibling tool lists voices, so the resource name alone distinguishes it from list_languages, list_files, and the other list_* tools.

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 routes the agent: 'Use a voice with supportsDirectToolExecution true for text_to_speech' names the downstream tool and the selection condition, and 'nextCursor fetches more voices' explains how to continue paging. It stops short of saying when to call this versus e.g. hardcoding a voiceId, so it is strong but not exhaustive.

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