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

Annotations already establish readOnlyHint=true, so safety is covered, but the description adds a genuinely behavioral fact: the URL is 'short-lived', telling the agent the result expires and should be consumed promptly. It stops short of stating the expiry window or any auth/scope requirements, but the added trait is real value beyond the annotations.

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?

One short sentence with zero filler, leading with the most decision-relevant property ('short-lived download URL'). Every clause earns its place.

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-only tool with no output schema, the definition covers what it returns and a key behavioral caveat. The only meaningful gap is how a caller obtains a valid file key, which an agent would otherwise have to guess.

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?

The single parameter has 0% schema description coverage — the schema only says 'key: string, minLength 1'. The description partially compensates by clarifying that the key identifies a stored file and giving concrete examples, but it does not describe the key's format or where an agent obtains a valid one.

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 resource (a download URL) and the input it derives from (a stored file key), with concrete examples of what a key represents. An agent can distinguish this from write-side siblings like upload_file. It does not, however, explicitly contrast itself with other URL-returning siblings such as get_invoice_pdf_url.

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?

There is no statement of when to call this versus alternatives, nor any prerequisites (e.g. that the key must come from a prior upload/list call). The parenthetical 'e.g. a receipt or report' only hints at usage context rather than guiding selection.

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