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

Annotations already declare readOnly/ idempotent/ non-destructive, so the safety profile is covered. The description adds one genuinely useful behavioral detail — a media item can be in a 'waiting for upload' state, meaning a fetched item may not yet be usable — but says nothing about missing-id/error behavior or authorization needs.

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?

A single tight clause with no filler, front-loading the key fact ('One media item'). It is a fragment rather than a sentence, but nothing is wasted.

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 one-parameter read tool with an output schema, the definition is borderline adequate: it need not explain return values, yet most of its text does exactly that while leaving the required media_id and not-found behavior unaddressed.

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 description coverage is 0% and the sole parameter media_id is undocumented in both schema and description. The description annotates the return object instead of telling the agent what media_id is or where to obtain it, so it fails to compensate for the coverage gap.

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 says it returns a single media item and enumerates the fields returned (status, kind, aspect, url, size, provenance), which separates it from the sibling list_media. However, it never states the verb 'retrieve by id', reading more like a return-field inventory than a purpose statement.

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?

No when-to-use guidance, no prerequisites, and no mention of the obvious alternative list_media (or add_media) despite their presence in the sibling set. The agent must infer that this is the single-item lookup counterpart.

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