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

Beyond the annotations (destructiveHint: true, readOnlyHint: false), the description adds critical behavioral context: messages are recoverable from Trash, the tool does not permanently destroy mail, it refuses already-Trashed messages, enforces a same-folder constraint, and operates on the whole UID set in a single call. This gives the agent a clear mental model of side effects and constraints.

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 sentences, each adding distinct value: core action, recoverability, preconditions and refusals, and batching guidance. The most important identifying information is front-loaded, with no filler or 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?

For a two-parameter tool with no output schema, the description covers the action, side effects, preconditions, refusals, and invocation strategy. The only minor gap is the exact behavior when a mixed set is passed (e.g., some UIDs already in Trash alongside valid ones) — whether the whole call fails or just the invalid subset is skipped. This does not prevent correct selection or invocation, but slightly reduces completeness.

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. The description adds a cross-parameter constraint not present in the schema: all UIDs must belong to the same folder, which affects how mailbox and uids must be combined. It also reinforces the batching behavior already described in the uids parameter, slightly redundant but still useful.

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 opens with a specific verb and resource: 'Move messages to the Trash folder', then anchors it with a familiar real-world analogy ('exactly as clicking Delete in Outlook or webmail would'). It further distinguishes this from permanent deletion, making the tool's scope unambiguous and separate from related operations like move_email or a permanent-delete tool.

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 provides explicit when-not-to-use guidance: it 'Refuses to run on messages that are already in Trash' and explains that permanent deletion is a separate operation this tool does not perform. It also gives a clear precondition ('All the messages must be in the SAME folder') and a concrete invocation rule ('Pass every UID in one call rather than calling it once per message').

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