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

With no annotations, the description must carry behavioral disclosure. It does disclose a metering/cost side effect ('meters 1 kvp_op') and the base64 return format. It remains silent on error behavior, permissions, or whether the operation is read-only, which keeps it from being stronger.

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 verb+resource; no filler. Each clause adds information: the operation, the metering cost, and the return encoding.

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 3-required-param tool with no annotations and no output schema, the description leaves too much to inference: no usage context, no parameter roles, and no error behavior. It covers the return encoding but misses details an agent would need to confidently construct a correct call.

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?

All three parameters have zero schema descriptions and the description adds almost no parameter semantics. It never explains the relationship between inboxId, messageId, and attachmentId or the expected ID formats, so the description fails to compensate for the 0% schema coverage.

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 the exact operation ('Download an attachment') and the response encoding, so an agent can distinguish it from message-level tools like inbox_message_get or inbox_message_raw. The parenthetical 'meters 1 kvp_op' is cryptic but does not undercut the action+resource clarity.

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 guidance about when to choose this over inbox_message_get or inbox_message_raw, nor about what inboxId/messageId/attachmentId should point to. The intended context is only implied by the tool name and required fields.

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