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

Annotations already declare readOnlyHint=false and destructiveHint=false, and the description adds genuinely new behavioral facts: the message receives a new id so it must be re-searched, and on Gmail a move out of a label removes only that label while the message persists in All Mail and other labels. That is exactly the non-obvious consequence an agent needs before calling.

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?

Four short sentences, front-loaded with the operation, then prerequisites, then the consequence, then the provider-specific caveat. Every sentence carries information an agent would otherwise get wrong.

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?

An output schema exists and annotations cover the safety profile, so the description only needs to cover invocation prerequisites and side effects—both of which it does, including the Gmail label nuance and the id-invalidation behavior.

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 coverage is 100%, so the baseline is 3, and the description adds provenance for message_id (a search_messages row) and the accepted forms of folder (path, name, or special-use like Archive). The folder semantics are largely echoed from the schema's own description, limiting the added value 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?

States a specific verb and resource ('Move one message to another folder of the same mailbox') and constrains scope to a single message, which distinguishes it from sibling mutation tools like trash_message or set_flags. An agent can identify the operation 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?

Explicitly directs the agent to obtain the message id from search_messages and the destination from list_folders or a special-use name, tying usage to specific sibling tools. It stops short of stating when not to use this tool (e.g., use trash_message for deletion), so it is clear context rather than full when/when-not coverage.

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