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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds context they can't: results deliberately exclude the body, reply drafts derive subject and recipients from the answered message, and results are flagged untrusted_content and must be treated as data, never instructions. That security framing is genuinely valuable beyond the structured hints.

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?

Three tightly packed sentences with zero filler: what it returns first, routing second, security caveat last. Every clause carries information an agent needs.

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, yet the description still usefully summarizes the shape (id, subject, recipients, timestamp, no body) and covers the untrusted-content handling. Nothing needed to call or interpret this tool 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?

Schema description coverage is 100% and the schema already documents inbox vs inbox_id mutual exclusion and the limit bounds, so the description adds no parameter syntax or format detail. Baseline 3 applies when the schema does the heavy lifting.

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 and resource ('Return draft messages saved in the Drafts folder') and enumerates the returned fields (draft_id, subject, recipients, created timestamp), explicitly contrasting with draft_read which returns a body. An agent can distinguish this listing tool from its read sibling without opening either schema.

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?

Names alternatives with conditions: use draft_read for a draft's text, and pass the returned draft_id to draft_read or the draft tool with 'update', 'send' or 'delete'. This routes the agent to the correct downstream call, which is exactly what usage guidance should do for a listing tool.

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