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

Goes well beyond the annotations by disclosing the key consequence that moved emails get new UIDs and that the result reports old UIDs as stale plus any UIDs the folder did not previously have. That result-shape detail is exactly what an agent needs to avoid reusing stale UIDs, and nothing contradicts the readOnly/destructive/idempotent hints.

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?

Three tight sentences: purpose and scope first, then the behavioral consequence, then the alternative routing. Every sentence carries distinct information with no repetition.

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 annotations covering safety/idempotency and an output schema present, the description only needs the purpose, the UID-mutation caveat, and the trash alternative, all of which it supplies. Minor gaps remain, such as what happens if the destination mailbox doesn't exist or whether message flags are preserved, but nothing essential to invoking it correctly is missing.

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 all four parameters are already documented in the schema and the description's job is limited. It adds only the implicit constraint that 'mailbox' and 'to_mailbox' must belong to the same account, and nothing about UID array semantics beyond the stale-UID note. Baseline 3 is 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?

States a specific verb and resource ('Move emails from one folder to another') plus the scope constraint ('in the same account'), and explicitly contrasts with the sibling trash_email. An agent can distinguish it from trash_email without opening either 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?

Names trash_email as the alternative when the destination is Trash and gives the condition (Trash's name isn't needed), and the 'same account' phrase implicitly excludes cross-account moves. No explicit when-not guidance beyond that, so not a 5.

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