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

Annotations cover safety (readOnly, idempotent, non-destructive, closed-world), and the description adds material context beyond them: the call opens a Tera Studio tool where the user picks the file, analysis runs in-browser and the file is never uploaded, and the tool reads only the file rather than identifying or playing songs. The privacy/local-processing guarantee and the interactive file-picker flow are exactly the kind of behavior an agent cannot infer from annotations.

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?

Four sentences, each doing distinct work: what it returns, how it runs and its privacy property, when to invoke it, and its boundary against the sibling. The capability statement is front-loaded and there is no filler or restatement of the title.

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 an output schema present, return-value explanation is unnecessary, and the description covers the remaining essentials: trigger conditions, the interactive flow, privacy handling, and the sibling boundary. Nothing an agent needs to select and call this zero-parameter tool 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 there is nothing for the description to disambiguate; baseline 4 applies. The description does clarify that the file is chosen by the user inside the opened tool rather than passed as an argument, which prevents an agent from expecting a file parameter.

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 (find musical key + tempo in BPM of a song file) and even specifies the output granularity (major or minor, with relative key). It explicitly contrasts with the sibling find_song_key, so an agent can distinguish the two 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?

Names concrete triggering contexts ("when someone asks what key or BPM a song is in, or wants to know before singing, mixing or practising it") and an explicit alternative with its selecting condition ("find_song_key looks up a well-known song by its title"). When-to-use, when-not, 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.