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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds real value by disclosing the return contents (headers, both body formats, attachment metadata) rather than a bare 'read' claim.

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 tight sentences with zero filler; the content-scope statement is front-loaded ahead of the usage hint.

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 and only three parameters, the description covers the essential call path and the shape of the returned data. It need not explain return values further, though a note on whether attachment bodies are fetched (vs. get_attachment) would fully close the loop.

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 uid, folder, and mailbox are already documented in the schema. The description reinforces uid's origin from list_messages but adds no new format or constraint details, so the baseline of 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 (read) and resource (a single message) and enumerates exactly what the response contains: headers, plain-text and HTML body, and attachment metadata. This clearly distinguishes it from list_messages, search_messages, and get_thread.

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?

"Use the uid from list_messages" gives a concrete prerequisite and source for the required identifier, and "ideal for extracting verification codes or sign-up links" signals an intended use case. It stops short of naming an explicit alternative (e.g., get_thread for conversations), so no full when-not guidance.

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