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

Annotations already declare destructiveHint=true, idempotentHint=true and readOnlyHint=false, and the description goes well beyond them: required auth scopes (message_delete/message_send/draft_write), the cascading attachment deletion, and the HTTP 409 draft_sending failure case. That is exactly the extra behavioral context the structured fields cannot carry.

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?

Front-loaded with the usage trigger, then permissions, inputs, side effects, error case and return shape — nearly every sentence earns its place. The 'Inputs: inbox_id (required), draft_id (required)' clause is the one redundant piece since the schema already marks both required.

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?

For a destructive 2-param tool with no output schema, the description covers auth, cascade behavior, failure mode, and even the return payload, so an agent has everything needed to call it correctly and handle errors.

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 coverage is 100% and both parameters are fully documented there (draft_id as dft_…, inbox_id as inb_…/username/email). The description only restates that both are required, adding no syntax or format detail beyond the schema, so the baseline 3 applies.

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+resource (delete a draft) and immediately scopes it with 'including a scheduled send you want to cancel', which cleanly separates it from siblings like cooper_send_draft and cooper_update_draft. An agent can pick this 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?

Gives clear when-to-use guidance ('when a draft should be discarded, including a scheduled send you want to cancel'), which implicitly routes away from send_draft. It stops short of naming explicit alternatives or when-not-to-use conditions, so it is clear context rather than full routing.

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