list_messages

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

Beyond the readOnly/idempotent annotations, it discloses that bodyPreview is deliberately empty because the provider's preview may leak text, that email content is untrusted data, and that an unknown folder or missing account yields [] rather than an error. These are exactly the behavioral details 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?

Front-loaded with purpose, then return fields, then the exclusion and its rationale, then operational caveats — a logical order with little waste. The parenthetical about bodyPreview is slightly convoluted but justifies itself by explaining a non-obvious empty field.

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 four-parameter read tool with an output schema, the description still covers the returned summary fields, the empty-body caveat, the empty-list failure mode, and the untrusted-content warning. There is no material gap an agent would need to close before calling it.

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 top, skip, folder and account_id are already fully documented in the schema. The description only reinforces the 'newest first' ordering tied to top/skip and adds no new format or edge-case detail for the parameters.

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 ('List messages in a mailbox folder'), plus the ordering ('newest first') and the exact shape of each summary ({id, subject, from, receivedDateTime, isRead, hasAttachments}). It also explicitly excludes bodies/previews, which separates it from read_message and search_mail without needing 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?

Gives an explicit follow-up path: use read_message with the returned id when bodies are needed, which defines the boundary of this tool's purpose. It does not, however, contrast itself with search_mail or list_unread, which an agent may confuse for a comparable listing operation.

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