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

The description discloses important behavioral details beyond annotations: it 'clears the cancellation', 'renews normally at the next cycle boundary', and notes 'No new charge — the cycle was already paid'. It also reveals the return shape and auth requirement ('Owner-only; requires a token minted with the billing scope'), giving the agent a full picture of side effects and prerequisites.

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?

Every sentence earns its place: purpose, condition, effect, no-charge clarification, exception, return payload, and auth requirement. It is front-loaded with the core action and remains readable despite covering multiple facets.

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?

With only one parameter, no output schema, and minimal annotations, this description fully compensates by covering behavior, exceptions, return value, and access constraints. The agent has enough context to invoke it correctly and anticipate outcomes.

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% with a clear description and example for addonKey, so the schema already carries the parameter meaning. The description adds no further parameter-specific semantics, which is acceptable given the baseline of 3 for well-covered schemas.

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 opens with a specific verb+resource: 'Resume (un-cancel) a pending-cancel add-on', clearly distinguishing it from sibling tools like subscribe_addon or cancel_line_publish. It also adds the precise condition 'whose paid-through cycle has not yet ended', making the tool's scope 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 states exactly when to use the tool: for pending-cancel add-ons whose paid-through cycle has not ended. It also gives a clear exclusion: 'Stackable add-ons cannot be resumed; buy a new unit instead', providing an actionable alternative.

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