Cancel outgoing email

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

Annotations already declare destructiveHint=true, idempotentHint=true, and readOnlyHint=false. The description adds substantial context beyond these: it explains the destructive nature ('The message is destroyed rather than paused'), idempotency ('nothing happens twice'), and the fact that it never reaches a mail server. It also clarifies that cancellation is not reversible. No contradiction with annotations; description enriches the agent's understanding.

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 fairly long but every sentence contributes critical information about limits, idempotency, destructiveness, and scope. It is front-loaded with the core action and then systematically covers exceptions and safety. While concise would be shorter, the structure is logical and efficient; a 4 is justified for its clarity and organization.

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 tool with one parameter, an output schema (not shown but present), and rich annotations, the description covers all necessary behavioral aspects: what happens when already sent, when already cancelled, repetition safety, irreversibility, permission boundaries, and how to verify. It addresses edge cases and gives the agent complete information to act reliably. This is a model description.

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?

There is one parameter (outgoingEmailId) with 100% schema description coverage: 'The identifier of the queued message, exactly as the sending tool returned it in outgoingEmailId.' The description does not add additional parameter-level details beyond this, but the schema already fully explains it. Baseline 3 is appropriate since the schema does the heavy lifting and the description doesn't need to compensate.

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 purpose: 'Stops a message you queued from being sent, while it is still waiting.' It uses a specific verb (stops) and resource (message you queued), and distinguishes itself from siblings by explicitly noting it cannot recall already-transmitted messages and mentioning get_outgoing_email as an alternative. This fully clarifies what it does and differentiates it from related tools.

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 provides explicit usage guidance: it says when to use (while waiting), when not to use (after transmission), and gives constraints such as 'You can only cancel a message you queued yourself.' It also advises checking the returned state or calling get_outgoing_email rather than assuming success. This is more than enough for an agent to choose appropriately.

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