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

Strong disclosure beyond annotations: it is a paid operation (~$0.08 default engine cost, budgetUsd caps it, chargedUsd reports actual), requires the write scope, and writes an MP3 into the media library. It does not address what destructiveHint=true implies (whether an existing asset is overwritten or whether a failed/aborted generation still bills), which is the one behavioral gap.

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?

Front-loaded with what gets produced, then cost, then permissions — the highest-risk facts come early. The cost clause is dense and stacks several numbers into one sentence, which reads slightly run-on but 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?

Covers the full decision surface for a paid generative write: input semantics, duration bounds, cost cap and reporting, scope requirement, and an alternative tool. Return values are already covered by the output schema, so their omission from the description is not a gap.

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 100%, so baseline is 3; the description earns a bump by adding constraints the schema lacks — style must never name a real artist, lyrics must carry [Verse]/[Chorus] markers, and budgetUsd's default/max are surfaced inline as spend semantics rather than just types.

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 concrete verb and output: sing supplied lyrics in a described style, producing a 1–3 minute MP3 in the media library, returning media key plus sung lyrics. It also explicitly separates itself from the sibling plan_music (music bed under narration), so an agent can choose without opening either 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 the routing rule directly ('For a bed under narration use plan_music'), states the prohibition on real artists, and bounds the artifact (1–3 minutes). When to use, when not to, and the alternative are all present.

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