cancel_send

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

Despite minimal annotations (only destructiveHint: false), the description discloses key behaviors: returns canceled: false if already sent, and throws when PROTONMAIL_SEND_DELAY_SECONDS is 0. It doesn't mention the success return value, but it covers edge cases well.

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 three concise sentences with no filler. The main action is front-loaded, and limitations are stated efficiently without redundancy.

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 one-parameter tool with no output schema, the description covers the operation, edge cases, and error behavior. It lacks an explicit success return value, but the overall context is sufficiently complete for an agent.

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?

The schema already fully describes the only parameter (id) with 100% coverage, and the description adds no additional parameter semantics. Baseline 3 is appropriate since 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?

The description clearly states 'Cancel a send_email call that was queued', using a specific verb and resource. It also differentiates from sibling tools like cancel_snooze by referencing the PROTONMAIL_SEND_DELAY_SECONDS mechanism.

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 explicitly states when to use the tool (while the item is pending) and when not to use it (if delay is 0, it throws). It also clarifies the outcome if the item has already sent, giving clear usage guidance.

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