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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false), yet the description adds substantive behavior: a hard cap of 15 mailboxes per call, address-order processing, and the pagination contract (skipped mailboxes named in the response, nextOffset fed back as offset). This is exactly the kind of multi-step disclosure that annotations cannot carry.

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, front-loaded with the core action, then filters, then pagination. No filler and no repetition of the title.

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?

No output schema exists, and the description compensates by describing the response shape (results tagged by mailbox, skipped mailboxes named, nextOffset returned). Combined with the 100%-covered input schema, an agent has everything needed to call and paginate correctly.

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% and every parameter is documented inline (including folder default and ISO 8601 dates), so the schema does the heavy lifting and the baseline is 3. The description reinforces the domain/offset usage but adds no syntax or format detail beyond what the schema already states ('use nextOffset from the previous call').

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 ('Run one search across every reachable mailbox') plus the key scope modifier ('optionally limited to one domain'). It explicitly anchors itself against the sibling search_messages ('Same filters as search_messages'), so an agent can distinguish the two without opening a 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 a real precondition ('at least one filter required') and frames the tool as the multi-mailbox counterpart to search_messages. It stops short of an explicit when-not-to-use rule (e.g. 'use search_messages for a single mailbox'), leaving that routing to inference from the name.

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