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

Annotations already indicate destructiveHint=true, so the description does not need to repeat that. It adds context about the ID format and the need for user approval, but does not detail other behavioral aspects like side effects or authentication requirements.

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 concise sentences that front-load the purpose and distinction. The usage guideline is placed at the end. Every sentence earns its place, though the structure could be slightly improved by separating the condition more explicitly.

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?

Given the high parameter count (12) and nested objects, the description is too brief. It does not cover the breadth of the tool or explain the schema parameters. The presence of an output schema reduces the need for return value details, but the overall context remains incomplete.

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 low (17%). The description only adds a note about the 'id' parameter format (starts with 'msg_'). For the other 10 parameters, including complex objects like 'to' and 'cc', no additional meaning is provided beyond 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?

The description clearly states the tool replies to a stored ShipMail message identified by ID starting with 'msg_'. It also distinguishes a sibling tool for JMAP inbox IDs, making the purpose unmistakable.

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?

The description specifies that the tool should be used only after user approval of recipients and content, providing a clear condition. It also names the alternative for JMAP inbox messages. However, it does not explicitly list when not to use it beyond the distinction.

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