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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds no behavioral context beyond that: no pagination, result limits, folder-resolution behavior, or what happens with an invalid folder name.

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 short sentences with the action front-loaded and the examples immediately following; nothing is padded. The phrasing "Search a folder" is slightly loose (it searches messages within a folder) but costs no extra length.

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?

An output schema exists, so return values need not be described. However, for a two-parameter search tool the folder parameter is undocumented and there is no routing guidance against six sibling tools, leaving the definition only minimally complete.

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 0% and neither parameter is documented in the schema, so the description must compensate. The criteria examples (ALL, UNSEEN, FROM alice@example.com) meaningfully clarify that parameter's accepted syntax, but the folder parameter and its INBOX default are left completely unexplained.

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 ("Search") and resource scope ("a folder"), and the name search_messages makes the target unambiguous. It does not differentiate itself from siblings like read_message or list_folders, but the core action is clear.

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?

There is no statement of when to use this tool versus read_message or list_folders, nor any mention of prerequisites or when results would be empty. The only guidance is syntax examples for one parameter, which is not usage guidance.

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