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

Annotations only declare read-only/idempotent/open-world; the description adds non-obvious behavior: the score is generated lazily on first request, it costs credits for ACE-Step songs but is free for acemusic models, and the response may be a still-reading status rather than the payload. These are billing and latency traits the annotations cannot express.

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 dense sentences, each carrying distinct information: what it returns, what it costs and when it is computed, the alternative tool, and the response shape. Nothing is repeated and the format/alternative are front-loaded.

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 usefully names the return shape ({ abc } or a still-reading status) and the cost model, which is enough to call it safely. Minor gap: it does not say whether re-requesting after a still-reading status re-incurs a charge.

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% and the songId description already explains the required format and source tools, so the description adds nothing new about the parameter beyond a passing mention of the song. Baseline 3 applies when the schema does the work.

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 ('The sheet-music score of a finished song in ABC notation') and immediately distinguishes itself from the sibling that returns other formats: 'For a MusicXML or MIDI file use acemusic_download_song.' An agent can disambiguate 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 explicit routing guidance for the format choice and names the alternative tool, which is the main decision an agent faces here. It does not cover other conditions (e.g., when the score is still being read, or whether repeated calls re-bill), but the primary when-to-use context is clear.

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