Search mail messages

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

Annotations already cover readOnly, idempotent, and non-destructive behavior, so the burden is on behavior beyond that. The description adds high-value traits: results are not in date order in $search mode, $search supports no date syntax, $filter only matches subject substrings, and the response reports which mode ran. This is substantial behavioral disclosure that structured fields cannot convey.

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?

The description is dense but every clause earns its place: projection, pagination, mode selection, ordering, and a workaround for the body-text-with-date limitation. The most important scoping fact (text search) is front-loaded, and there is no filler or restatement of obvious annotation data.

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 search tool with no output schema, the description tells the agent what projection to expect (via mail_list_messages), the default page size and cap, the mode behavior, and how to compensate for mode limitations. Nothing an agent needs to invoke it correctly or interpret its response is missing.

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?

Although schema coverage is 100%, the description adds meaning the schema alone cannot: after and before are not just date filters but mode switches, and query changes semantics depending on whether a date range is present. This directly affects correct invocation and interpretation of results, going well beyond the schema's property-level descriptions.

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: "Finds messages by text," and immediately distinguishes it from mail_list_messages via the "same compact projection" reference. The two-mode explanation further separates it from both a plain list operation and a generic search, so an agent can select it confidently.

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 explicitly states when to use each mode: no date range triggers $search, while passing after/before triggers $filter, and it explains the trade-offs of each. It even gives a concrete fallback strategy for searching body text within a period, which is exactly the kind of actionable usage guidance an agent needs.

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