List and search messages

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

Annotations only declare readOnlyHint, so the description must supply behavioral depth. It adds sorting (newest first), output scope (summaries only), and a performance trait (server-side filter execution). This goes well beyond the annotation without contradicting it.

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 short sentences, no filler, with the core behavior and ordering in the opening line. Every sentence carries a distinct fact: filtering options, no-criteria behavior, server-side performance, and summary-only return. This is appropriately compact for a 12-parameter tool.

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 tool with no required parameters and a fully described schema, the description covers the behavior that matters: ordering, summary output, body alternative, and paging behavior. It doesn't describe exact summary fields or explicitly distinguish all sibling tools, but the schema and the get_message pointer fill most of the gap. Given no output schema, the 'summaries only' statement is sufficient directional guidance.

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 already documents all 12 parameters, so the baseline is 3. The description adds a useful grouping of filter types and clarifies that omitting criteria turns the call into a page-through of the mailbox. It also ties filtering to server-side execution, which is operational context the schema does not provide.

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 ('Lists messages newest first') and enumerates the viable filters, including sender, recipient, subject, body, date range, and flags. It also points to get_message for full body, which helps disambiguate from sibling list/get tools. However, it never explicitly contrasts this with list_new_messages, so sibling differentiation is incomplete.

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?

It states when to page without criteria and why: 'With no criteria it simply pages through the mailbox' and 'searching a large folder is cheap' due to server-side filtering. It explicitly routes body retrieval to get_message: 'Returns summaries only — use get_message for the body.' It doesn't mention when to prefer list_new_messages over this tool, so exclusions are partial.

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