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

Annotations already declare readOnly/idempotent/non-destructive, so the burden is lower, but the description still adds real context: the ~5 minute expiry window, charset=utf-8 serving for text-like types, and the Content-Disposition effect of disposition=attachment. It does not say what the response body looks like (bare URL vs object), which is the main remaining gap for a tool with no output schema.

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?

Front-loaded and reasonably short, but the first sentence merely restates the title verbatim, and the third sentence re-repeats 'Short-lived presigned GET URL' before adding the 5-minute figure. The S144/D146 reference codes are noise for an agent. Two of four sentences carry redundant framing.

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 2-parameter read tool with no output schema, the description covers the prerequisite, lifetime, and download-mode behavior adequately. The one thing an agent might still want — the exact shape of the returned value — is not stated, but the nature of a presigned URL makes that largely inferable.

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 only 50% — attachment_id has no schema description — but the description compensates by explaining it must come from list_attachments/attach_file and that it is a UUID-backed attachment reference. disposition is already documented in the schema and the description reinforces download-vs-open semantics with the original-filename detail.

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 (get) and a specific resource (short-lived presigned GET URL for an attachment), and the parenthetical scopes it to md-renderer image use. An agent can distinguish it from list_attachments or read_file without opening any 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?

Explicitly tells the agent where the attachment_id comes from (list_attachments or attach_file) and how to handle the short lifetime (fetch immediately, ask again after expiry). It stops short of naming when a different tool would be preferable (e.g. read_file for text content), so it is clear context rather than full alternative routing.

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