download_attachment

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

Annotations already declare readOnly=true, idempotent=true, destructive=false and openWorld=true, so safety is covered. The description adds genuinely new behavior: the payload comes back as Base64 and is bounded by MAIL_MAX_ATTACHMENT_BYTES, a size constraint the annotations do not express.

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 front-loaded sentence carrying the action, encoding, and limit with zero filler. 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 simple read tool with no output schema and full annotation coverage, the description adequately covers format and size cap. It still leaves open what happens when the attachment exceeds MAIL_MAX_ATTACHMENT_BYTES (failure vs truncation) and leaves all four parameters unexplained.

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% across four parameters (emailId, attachmentId, folder, accountId), and the description compensates only faintly by implying an attachment belongs to a message it owns. It says nothing about the inbox/sent enum, the accountId scoping, or required-vs-optional behavior.

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 states a specific verb and resource ('Read an attachment from an owned message') plus the return encoding (Base64), which is enough to distinguish it from list_attachments. It does not name or contrast any sibling explicitly, so it falls short of the 5 bar.

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?

'from an owned message' hints at a scope prerequisite, but there is no statement of when to reach for this tool versus list_attachments (discover the attachmentId first) or get_message. No alternatives or exclusions are offered.

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