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

Beyond the annotations, the description discloses important behavior: the message is returned inside a delimited untrusted block, sender checks are included, and text hidden from readers is omitted. It also gives explicit security handling guidance about not following email instructions and confirming with the user before acting. This is substantial behavioral context that annotations alone do not provide.

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 definition is front-loaded with the core action and returned content, then moves to filtering behavior and security guidance. It is efficient overall, though the security warning is relatively long and could be tightened without losing meaning.

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?

The tool has a rich output schema and clear annotations, so the description need not explain return values or safety hints. It does add important context about untrusted message content and hidden-text omission. The main remaining gap is sibling differentiation for tool selection.

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 mailbox and message_id are already documented in the input schema. The description adds no parameter-specific syntax or constraints beyond what the schema provides, making the baseline score appropriate.

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 states a specific verb and resource: get one message, not a thread or list. It also names the returned content: text a person would see, one-time codes, links, and sender checks. It does not explicitly distinguish itself from siblings like get_email, get_mailbox_thread, or wait_for_mailbox_message, so it stops short of a 5.

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?

Usage is implied by 'Get one message,' which suggests retrieving a single message by id. However, the description gives no explicit when-to-use guidance versus get_mailbox_thread, search_mailbox_messages, or wait_for_mailbox_message, and it names no alternatives or exclusions.

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