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

Annotations already declare readOnlyHint=false, destructiveHint=true and idempotentHint=true, so the safety profile is covered. The description adds genuinely new behavior: billing resumes on the existing schedule and the customer may be charged, which is the key side-effect an agent needs before calling a money-affecting mutation.

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?

Two tight sentences with the write-nature and operation front-loaded, followed by the sibling disambiguation and the billing consequence. Nothing is redundant.

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 mutation with rich annotations and no output schema, the description covers purpose, alternative, and the customer-visible consequence. Only the reversion path (how to cancel again) is left unstated, which is minor.

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 the single parameter is documented in the schema as the subscription `id` rather than `internal_id`. The description adds no further parameter meaning, which is acceptable at this coverage level, 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 and resource ('Reactivate a cancelled subscription') and immediately disambiguates it from the near-duplicate sibling resume_subscription ('the effect is the same as resume; use this for cancelled ones'). An agent can pick between the two without opening either 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?

Gives a clear selection rule: this tool is for cancelled subscriptions, resume is effectively equivalent. It stops short of an explicit negative case (e.g. 'do not use on paused subscriptions – use resume_subscription'), so the routing is strong but inferential on the exclusion side.

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