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

Annotations already establish the safety profile (readOnlyHint=false, idempotentHint=false, destructiveHint=false, openWorldHint=false). The description adds substantive context beyond them: the base64 encoding requirement and the hard constraint that byte-length must exactly match the reportLen declared at CREATE time. It does not state what happens on a length mismatch (error vs. silent drop), keeping it short of a 5.

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 tight sentences, front-loaded with the action and device relationship, followed by the payload constraint, the scope limitation, and the routing advice. Every sentence carries information; no filler.

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 no-output-schema mutation primitive, the definition covers prerequisite, payload encoding, payload-length constraint, and when to prefer the alternative. The only minor gap is error/failure behavior on an invalid report length, which is not addressed.

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 meaningfully enriches the parameters by explaining that reportBase64 is base64 and that its byte-length must match the CREATE-time reportLen — a cross-call constraint the schema cannot express. It adds real semantics beyond the field descriptions.

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 (Send) and resource (HID input report) tied to a previously created UHID device, and names the sibling it depends on (device_uhid_create). It also distinguishes itself from device_type by declaring it is a 'generic raw-report primitive ... not text-aware.' An agent can place it precisely in the UHID tool family.

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?

Explicitly says 'Prefer device_type to type a string; use this only when you need to compose the exact reports yourself,' naming the alternative and the exact condition that selects this tool. It also states the prerequisite (prior device_uhid_create call), leaving nothing to inference.

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