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

Annotations only declare readOnlyHint=true (safety profile), so the description carries the rest. It usefully discloses the return contents (plain-text body, web_link), which is valuable given there is no output schema. It does not cover error behavior for a bad id or cross-mailbox resolution, keeping it short of a 5.

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 tightly written sentences: the what (fetch one message plus return fields) is front-loaded, followed by the routing rule. No filler.

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 annotations covering safety and no output schema, the description compensates by naming the returned fields, and the schema covers both params. Only minor gaps remain (error/missing-id handling), so it is complete enough for correct invocation.

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%, including the account param's 'omit to use every connected mailbox' semantics, so the schema already does the heavy lifting. The description only echoes 'by its id' and adds no format or scoping detail beyond the schema, matching the baseline 3.

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 (fetch/read) plus resource (one Outlook message) and even names the payload returned (plain-text body and web_link). It is clearly distinguishable from search_outlook_messages, which locates rather than retrieves a message.

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 names the alternative tool (search_outlook_messages) and the two triggering conditions: a message found via search, or a triggering event supplying a message_id. Nothing about when to select this tool is left to inference.

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