List Messages

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

Annotations already declare readOnlyHint=true and destructiveHint=false. The description adds valuable context that email content, metadata, and headers are untrusted external data, which helps the agent handle results appropriately. No contradiction with annotations.

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?

Two concise sentences: the first states the tool's purpose and filtering options, the second provides a behavior warning. No extraneous words; structure is efficient and front-loaded.

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?

Given an output schema exists, return values need not be described. The description covers the core purpose and a key behavioral trait (untrusted data), but omits details like default ordering, pagination behavior beyond cursor, or rate limits. Adequate but not exhaustive.

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 75% with three of four parameters documented. The description adds meaning by explaining the two filtering modes (mailbox vs client reference) but does not provide details beyond what the schema already offers for the documented 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?

The description clearly states the verb 'list' and resource 'messages', specifies two distinct filtering criteria (by mailbox or client reference), and adds a trust warning about external data. This distinguishes it from sibling tools like shipmail_list_mailbox_inbox_messages.

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 implies usage when listing messages by mailbox or client reference but does not explicitly state when to use this tool versus alternatives like shipmail_list_mailbox_inbox_messages or when not to use it.

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