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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description does add real behavioral context beyond them: the 10 MB limit and the fact that 'inline' changes the payload to include content. It still omits what happens when an attachment exceeds 10 MB, whether the resource link is a URL with an expiry, and any auth requirements.

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?

Two short sentences, front-loaded with the core action and immediately followed by the size constraint and the inline behavior. No filler or restatement of the title.

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?

With no output schema, the description does useful work in sketching the return (metadata, resource link, optional content), but it leaves the meaning of accountId and the failure mode for oversized attachments undefined. For a 4-parameter download tool with zero schema documentation, that is adequate but incomplete.

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%, so the description carries the full burden and explains only one of four parameters ('inline'). accountId is completely unexplained (which account? required for multi-account?), and messageId/attachmentId are left to their names alone to convey scope and source.

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 metadata and a resource link for one attachment') and adds a size cap and the inline variant. An agent can tell this is attachment-scoped rather than message-thread scoped, though it never explicitly contrasts with siblings like get_email or get_thread that also return attachment data.

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 mention of prerequisites (e.g. the message/attachment must already exist or how to discover an attachmentId), and no routing against alternatives such as get_email for locating attachments. The agent must infer the calling context entirely.

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