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

The readOnlyHint annotation already establishes this is a safe read. The description usefully adds that the full message body is returned (as opposed to a truncated listing), but says nothing about pagination, error cases, or what happens with an invalid id/conversation pairing.

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?

A single front-loaded sentence delivers the core capability, followed by a short API reference. Nothing is padded, though the raw endpoint string is of marginal value to an agent that already has the parameters.

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 carries the return-value burden, and it partially does so by noting the full body is included. However, it does not describe the message object's structure or fields, leaving the agent to discover the response shape at call time.

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 both parameters are already documented in the schema. The description adds only the REST path mapping ('GET /conversations/{conversation_id}/messages/{id}'), which corroborates but does not extend the schema; 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 single message, including the full body') and implies the single-vs-list distinction against missive_list_conversation_messages. It does not name the sibling explicitly, so the differentiation is left to inference.

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?

There is no explicit guidance on when to use this tool versus the many list/get siblings, nor any stated prerequisites or exclusions. The only usage signal is the implicit sense of fetching one message rather than many.

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