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

There are no annotations, so the description carries the full behavioral disclosure burden. It does disclose one behavioral trait: 'meters 1 kvp_op', which appears to indicate a usage/metering cost. However, this phrasing is cryptic, and the description does not clarify read-only behavior, permissions, return format, or side effects.

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?

The main instruction is front-loaded and compact: 'Download raw MIME for a message'. However, the trailing parenthetical '(meters 1 kvp_op)' is unclear, poorly integrated, and potentially confusing. Conciseness is good, but the sentence does not fully earn its clarity.

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 two-parameter download tool, a brief description can be adequate, and 'raw MIME' partially indicates the return payload. But with no annotations and no output schema, the description should more explicitly state what is returned, whether this is read-only, and where the IDs come from. The cost/metering hint is useful but ambiguous. The definition is minimally viable but not complete.

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% and the description does not compensate by explaining the parameters. The parameter names inboxId and messageId are reasonably self-explanatory, and messageId's role is lightly implied by 'for a message', but the description provides no details on ID provenance, formats, or how they relate. For low coverage, the description should have added at least minimal parameter context.

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 clearly states the action and resource: 'Download raw MIME for a message'. The 'raw MIME' phrasing helps distinguish it from parsed message tools like inbox_message_get or inbox_messages_list, though it does not explicitly name the siblings. The parenthetical 'meters 1 kvp_op' adds noise and slightly detracts from purpose 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?

The use case is implied by the word 'raw' — an agent can infer this is for when the unparsed MIME source is needed rather than a processed view. However, the description gives no explicit when-to-use guidance, does not mention alternatives, and does not state when not to use this tool. The guidance is present only by implication.

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