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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, so the safety profile is covered. The description still adds real behavioral context beyond them: this is a live read (not cached), the mp3 link is permanent while playUrl is a fresh direct player link that expires at playUrlExpires (~1 hour), and stems appear only if the song was split. That expiry asymmetry is the kind of detail an agent could not get from structured fields.

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?

One front-loaded paragraph: purpose first, then the returned-field inventory, then sibling routing, then the HTTP path. The field list (status, title, style, lyrics...) is somewhat enumerative but each item tells the agent something about coverage, so it mostly earns its place.

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?

There is no output schema, so the description must carry the return-value burden — and it does, listing the fields returned and flagging the conditional stem output and URL expiry. Combined with annotations covering the read-only profile and a fully documented single parameter, 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?

There is only one parameter and schema coverage is 100%, with the schema itself explaining where a songId comes from and that it runs on the owning account. The description reinforces this by pointing at acemusic_list_songs and the path template, but adds no syntax or format detail beyond the schema. Baseline 3 applies when the schema does the heavy lifting.

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?

The description opens with a specific verb+resource ("One song read live from ACE Music") and enumerates exactly what comes back: status, title, style, lyrics, duration, model, mp3 link, playUrl, cover, stems. It also names the siblings it is not (acemusic_list_songs, acemusic_download_song), so an agent can separate it from neighbors without opening a 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?

It explicitly routes the agent: use acemusic_list_songs to obtain songIds, and acemusic_download_song for WAV / MIDI / MusicXML. The condition that selects the alternative is stated, not inferred, and the endpoint (GET /music/{songId}) confirms the read-only access pattern.

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