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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds behavioral detail beyond annotations: it specifies that results include only 'pending' or 'sending' statuses, are ordered by scheduled send time, and that the response contains an `id` usable for cancellation. This adds useful context without contradicting any annotation.

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 two concise sentences with zero fluff. The core purpose and key details (status filter, ordering) are front-loaded in the first sentence, and the second sentence adds a crucial cross-reference to the cancel action. Every phrase earns its place.

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 the presence of an output schema (which would document return fields) and annotations covering safety, the description is sufficiently complete. It explains the status filter, ordering, optional inbox filtering, and the existence of an `id` for cancellation. It covers all the practical information an agent needs to call the tool correctly, and the limit parameter is documented in the schema.

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 schema fully documents all three parameters. The description only mentions 'filter by inbox' generically and does not clarify the relationship between `inbox` and `inbox_id` beyond what the schema already says. Since it adds no meaningful parameter-specific information beyond the schema, the baseline of 3 is appropriate.

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's verb ('List'), resource ('pending scheduled email sends'), and scope ('for the workspace'). It distinguishes itself from the sibling 'schedule' tool by explicitly noting that canceling is done via the schedule tool. The status filtering ('pending' or 'sending') and ordering by scheduled time add specificity beyond a generic list.

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?

While not explicitly stating 'when to use this vs. alternatives', the description gives a clear use case and routes the user to the schedule tool for canceling. The optional 'filter by inbox' guidance and the mention of using the returned `id` for cancellation provide practical context. It doesn't enumerate all exclusions but adequately separates listing from other operations.

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