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

The description adds behavioral context beyond annotations: it reveals that cancellation is irreversible and contingent on the message's status being 'scheduled'. Annotations already indicate destructiveHint=true and idempotentHint=true, and the description aligns with those. It does not detail side effects or error behavior, but for a simple cancel operation this is adequate.

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 short sentences with no wasted words. The key action and constraint are front-loaded in the first sentence. Every sentence adds value 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 simple tool with one required parameter and no output schema, the description covers the essential aspects: purpose, precondition (scheduled status), and irreversibility. It does not explain the return value or error cases, but these are often inferred for a cancel operation. The description is sufficient for an agent to use the tool correctly given the context.

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% and the single parameter 'id' is already described as the UUID of the scheduled message. The description does not add any additional meaning or context about the parameter, so it relies entirely on the schema. Baseline 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 action 'Cancel a scheduled message' and specifies the resource. It also provides a condition (only scheduled messages) that distinguishes it from other message-related tools like delete or update. Although it doesn't explicitly name sibling alternatives, the verb and constraint make the purpose unambiguous.

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: to prevent a scheduled message from being sent, and notes that only messages with status 'scheduled' can be cancelled. It also warns that the action cannot be undone. It does not explicitly say when not to use or compare to alternatives like update_scheduled_message, but the guidance is clear for most scenarios.

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