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

Annotations only supply destructiveHint=true; the description adds real behavioral context beyond that — the operation is only valid pre-send, it fails once the window has passed, and it avoids billing. It does not say whether the postcard object is returned or whether a cancelled postcard can be recreated, which keeps it short of a 5.

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?

One front-loaded sentence carries the purpose, precondition, failure mode, and billing consequence; the trailing API endpoint line is a compact and useful mapping. No filler.

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 single-parameter destructive tool with no output schema, the description covers purpose, precondition, and failure well. It leaves the return payload and any idempotency/retry behavior unstated, which is a minor but real gap.

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 a single parameter and the schema already documents it at 100% coverage, including the psc_ prefix format. The description adds nothing about the id beyond restating that it identifies the postcard, 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 (cancel) and resource (postcard) plus the exact scope constraint (before send_date) and the outcome (never mailed, not billed). No sibling tool performs cancellation, so it is unambiguously distinguishable from the create/get/list family.

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 context for when the tool applies (before send_date) and an explicit failure condition (send window passed), which tells the agent when not to attempt it. It names no alternative tool, but none exists among the siblings, so the only gap is the absence of a stated workaround.

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