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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so 'Read-only operation' is largely redundant. However, the description adds genuine value beyond annotations by disclosing the required auth ('narrador:files scope (OAuth) or nrd_files_* API key'), which no structured field provides.

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?

Three tightly packed sentences: purpose first, return shape second, usage and auth third. No filler and the routing hint is placed where an agent will read it.

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?

With no output schema, the description compensates by enumerating the returned voice fields, and it supplies the auth requirement and the downstream tool that consumes the ids. Nothing needed to call this no-arg tool 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?

The tool takes zero parameters, so per the rubric the baseline is 4. The description instead documents the return shape (id, name, provider, defaultAccent, isPublic, description, sample URL), which is useful given there is no output 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 (Returns) and resource (all voices available for narrador files TTS jobs), and enumerates the fields each voice carries. An agent can immediately distinguish this list tool from siblings like create_files_job or get_files_job.

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 id from this list when calling create_files_job,' naming the consumer tool. It does not state when-not to use it or describe prerequisites for the lookup itself, so it falls just short of a full 5.

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