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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds real domain behavior on top: the ~3% natural / ~16% usable tempo thresholds and the fact that half and double time count. It also enumerates what comes back, including a link to build the matched audio.

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?

The purpose is front-loaded in the first clause and the rest is dense, load-bearing detail about thresholds and return values. It is a long run-on listing several return fields, but with no output schema each 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?

For a four-required-param read-only computation with no output schema, the description covers purpose, domain thresholds, verdict semantics, and the shape of the response including the audio-matching link. Nothing needed to call or interpret it 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?

Schema coverage is 100%, so the baseline is 3, but the description adds directional meaning the schema only implies: track B is the one being changed, so the returned target BPM and semitone shift apply to B. Key format and BPM ranges are left entirely to the schema, which is fine given full coverage.

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 names a specific verb and outcome ("Decides whether two songs will mix well") and states the exact inputs used (keys and BPMs) plus the method (Camelot wheel, DJ tempo limits). That clearly separates it from single-purpose siblings like camelot, tempo_change, or transpose, though it never names them explicitly, so it falls just short of the top mark.

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?

"Decides whether two songs will mix well" implies the use case: a combined compatibility verdict rather than an individual key or tempo calculation. It gives no explicit when-not guidance or named alternatives, so it is clear context without exclusions.

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