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

With only generic annotations (write/idempotency hints), the description carries real weight: it discloses that download links expire after 1 hour, that the input is downloaded server-side into Cloudflare R2, that processing runs via a headless browser, and that the input is deleted when the job ends. These lifecycle and retention facts go well beyond what the annotations state.

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 core differentiator is front-loaded in the first sentence, and the structure moves sensibly from purpose to input to options to outputs. The pipeline detail (R2, headless browser on Cloudflare) is mildly extraneous but short enough to be tolerable.

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 correctly fills the gap by explaining that download links are returned and expire after an hour. Input requirements, optional settings and storage behavior are all covered; only minor ambiguities remain, such as the units/semantics of tempoPercent and the vague qualifier 'where the tool supports them'.

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 nominally 100%, but the nested 'settings' object is intentionally unconstrained (additionalProperties: {} with no defined keys), so the description's enumeration of valid keys (tempoPercent, bpm) is genuinely necessary information the schema does not provide. It also names example format values and explains the conditional nature of bitrateKbps, adding meaning over the schema.

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+resource (changes tempo) and immediately qualifies it with the key differentiator 'without changing pitch', which separates it from siblings like speed_changer and pitch_shifter. An agent can route to it without opening the 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?

The phrase 'without changing pitch' implies when this tool is preferred over speed_changer, but no alternatives or exclusion conditions are named explicitly. Usage is inferable rather than stated, so this lands at minimum-viable.

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