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

Goes well beyond the readOnly/idempotent annotations: the URL expires in two minutes, is invalidated when the message or inbox is deleted, and the payload is flagged as untrusted. Those are exactly the operational facts an agent needs before planning a fetch-and-use sequence, and none of them duplicate the structured fields.

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?

Three short sentences, each doing distinct work: capability, prerequisite plus expiry, then a safety constraint. The scoping and the security warning are front-loaded rather than buried, and there is 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 three-parameter tool with no output schema, the description covers capability, prerequisites, lifetime and safety. The only shortfall is that the return shape is described only loosely ('download URL') without saying whether it arrives as a bare string or a field in an object, which matters when there is no output schema to consult.

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 100%, so id, messageId and attachmentId are already documented. The description only adds the ownership constraint implied by 'owned email message'; it does not explain ID formats or how to obtain id and messageId. Baseline 3 applies.

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 and resource: 'Get a private attachment download URL', scoped to 'an owned email message'. This is enough to separate it from list_emails (which enumerates messages) and download_temporary_file (which handles local temp files) 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?

Supplies a concrete prerequisite ('Requires an approved workspace key') and the description plus schema point at list_emails/wait_for_email as the source of the attachmentId. It never names an alternative tool or an explicit when-not-to-use case, so the routing is clear but not exhaustive.

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