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

Annotations already declare readOnlyHint=false and destructiveHint=false, so safety is covered. The description adds genuinely useful behavioral context that annotations cannot: the operation fails once the message is permanently removed by empty_trash or delete_message. It does not describe auth requirements or the response, but the key constraint is disclosed.

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 sentences, zero waste, with the core action front-loaded and the durability caveat placed second. Every clause earns its place.

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?

For a 4-parameter mutation with full schema coverage and a clear safety annotation profile, the description supplies the one non-obvious constraint (message must still exist). Return values are not described, but no output schema exists to require it; only minor gaps remain.

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, mailbox, and destination are already documented, including the Trash and INBOX defaults. The description only restates the source/target folder behavior, adding no syntax or format detail beyond the schema. Baseline 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 and resource ('Undo a delete or a spam mark: move one message out of Trash...back to the Inbox') and clearly distinguishes itself from delete_message, empty_trash, and move_message by framing it as a reversal operation. An agent can identify the tool without opening the schema.

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?

Gives clear context on when it applies (only while the message still exists) and the default source/target folders. It stops short of naming move_message as the alternative for non-restore moves, so it is not a full when/when-not/alternatives treatment.

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