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

readOnlyHint already declares the operation safe; the description adds behavioral detail that custom folders are included and unread counts are returned. No contradictions 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?

The description is concise with two sentences: first states the output, second provides usage timing. No unnecessary words or redundancy.

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 zero parameters, no output schema, and a readOnly annotation, the description fully covers what the tool does, when to use it, and the scope of folders returned.

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?

The tool has zero parameters, so the description need not explain parameter semantics. A baseline of 4 is appropriate since there is no parameter burden.

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 tool lists mailbox folders (Inbox, Archive, custom folders) with unread email counts. This specific verb+resource+scope distinguishes it from sibling ews_list_inbox, which lists messages rather than folders.

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 says to use this tool before moving an email to a non-standard folder, providing clear when-to-use guidance and implicitly distinguishing it from standard folder moves.

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