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 valuable behavioral context beyond annotations: it explains what is returned (pending sends, last week's finished sends, final statuses sent/cancelled/failed and why) and that each result carries an id and draft uid. It does not mention pagination or auth requirements, but those are minor given the annotation coverage.

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 compact and front-loaded, first stating what the tool returns and then adding the practical detail about the id and draft uid. Every clause earns its place, and there is no redundant repetition of the title or schema.

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?

With no output schema, the description takes responsibility for describing the return shape: pending messages, last week's finished statuses, cancellation ids, and draft uids. For a single-parameter read-only listing tool, this is complete enough for an agent to invoke and interpret results correctly.

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%, so the mailbox parameter is already fully documented by the schema. The description mentions 'from a mailbox' but adds no new syntax, format, or constraint beyond what the schema provides. Baseline 3 is appropriate when the schema carries parameter semantics.

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 resource and scope: messages waiting to be sent later from a mailbox, plus the last week's finished ones with their final status. It also distinguishes itself from the sibling cancel_scheduled by explaining that each item has an id used for cancellation. An agent can identify this as the scheduled-sends listing tool without opening the 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?

Usage is implied: this tool is for inspecting scheduled and recently finished sends, and the id field is explicitly linked to cancel_scheduled. However, the description does not state when to prefer this over list_messages or search_messages, nor does it provide any exclusion conditions. The guidance is adequate but not explicit.

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