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

Annotations already declare destructiveHint/idempotentHint, and the description adds real semantics beyond them: prepared letters are cancelled instantly with nothing sent or charged, paid letters are fully refunded, printed letters cannot be cancelled, and removing one item from a batch invalidates the batch approval. The destructive consequences are spelled out precisely, with no contradiction of the annotations.

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 core purpose and the cancellation outcomes, then alternatives, then batch mechanics. A few fragments ('Also a greeting card.') are abrupt and slightly slowing, but almost every sentence carries an operational fact.

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?

An output schema exists and the description still names the key failure result (TOO_LATE), which is the main thing an agent must handle. Coverage of refunds, contract vs. letter, and batch edge cases is thorough; only the terse greeting-card remark is left ambiguous.

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 already documents both ids and their formats, so the baseline is 3; the description earns more by adding the mutual-exclusion rule ('Then do not give letter_id') and the batch-approval consequence of cancelling a single item, which the schema does not state.

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 and resource ('stop a letter of this service', 'cancelled') and immediately disambiguates from the sibling concern it is most likely confused with: 'This tool does not cancel a contract.' An agent can separate it from prepare_letter/send_letter without opening any 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?

Explicit when-to-use plus alternatives: contracts are cancelled by preparing a letter with prepare_letter instead, and batch scope is selected by passing batch_id. It also gives the exclusion condition (already printed → TOO_LATE) that tells the agent when the call will not succeed.

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