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

Annotations declare readOnlyHint=false and destructiveHint=true, and the description adds genuinely useful behavioral context beyond that: the silent no-op when Music is closed, and the post-call state (player state, volume, track). It does not explain why the operation is flagged destructive or whether the change is reversible, which keeps it out of 5 territory.

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 short sentences, front-loaded with the action and range, then the no-op caveat, then the return state. No filler and nothing redundant.

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?

An output schema exists, so return values need not be spelled out, though the description helpfully summarizes them. Combined with the no-op caveat and full parameter coverage, an agent has what it needs; only the destructiveHint rationale is left unexplained.

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 100%, with 'volume' documented as 0 to 100 and 'confirm' documented as ignored for legacy clients. The description only restates the same 0–100 range, adding no semantics the schema doesn't already carry; baseline 3 applies.

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 ('Sets the Music app's volume') plus the valid range, which is enough to distinguish it from siblings like music_play, music_pause, and music_now_playing. It does not explicitly name those siblings as alternatives, so it stops short of a 5.

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?

Usage is only implied by the verb: call this to change the Music app's volume. The description does add an important precondition behavior ('Does nothing when the Music app is not open'), but gives no explicit guidance on when to prefer this over pausing/adjusting via other means or what to do when the no-op case is hit.

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