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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=false), so the bar is lower. The description adds genuine behavioral context not in structured fields: HTML bodies are converted to plain text, and attachments are returned with name/type/size/kind plus an attachmentId consumable by read_outlook_attachment and save_outlook_attachment_to_onedrive. It omits truncation behavior, which the schema covers instead.

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?

Three sentences, front-loaded with the verb and payload, then behavioral detail, then the ID sourcing hint. The em-dash enumeration of attachment fields is dense but each item earns its place; nothing is redundant.

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 does so reasonably: body text, plain-text conversion, and the attachment metadata shape including the reusable attachmentId. It could mention the maxChars truncation default in prose, but that is already in the schema.

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 coverage is 67%: mailbox and maxChars are documented, but messageId has no schema description. The description compensates directly for that gap by telling the agent where message IDs come from (search_outlook_messages or list_messages), which is the key semantic missing from the schema.

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 ('Read one message in full') and scopes it precisely to a single message, distinguishing it from get_outlook_conversation and the gmail/agentmail equivalents in the sibling list. The inclusion of body and attachment metadata makes the payload scope unambiguous.

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?

Explicitly routes the agent to the prerequisite tools: 'Get the message ID from search_outlook_messages or list_messages,' and names the downstream consumers of the attachmentId. It does not state when NOT to use it (e.g., use get_outlook_conversation for a whole thread), so it falls just short of the top band.

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