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

Annotations only declare readOnlyHint=false, destructiveHint=false, openWorldHint=true. The description adds substantial context: access persists to the end date, the change is reversible via reactivation in Recurly before expiry, it requires a Cotlet API key, and it triggers a per-call confirmation because it affects other people. None of this duplicates the annotations, and nothing contradicts destructiveHint=false.

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 critical facts (what it does, the timing options, the non-terminate distinction) are front-loaded. It is slightly long, with mild redundancy between 'access continues until the end date' and 'It stays active until then,' but no sentence is wasted.

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 mutation tool with no output schema, the description covers reversibility, edge cases, auth requirements, and confirmation behavior well. The only gap is that it does not hint at the resulting state/return, though with no output schema that burden is lower.

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%, so both parameters (subscription_id, timing enum) are already fully documented, including the timing default. The description restates the enum values but adds no syntax or format detail beyond the schema, so 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 ('Cancel a subscription so it stops renewing') plus the key scope fact that access continues until the end date. It is clearly distinguishable from siblings like recurly_change_subscription and recurly_postpone_subscription, which the description implicitly rules out via 'It does not terminate.'

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?

Explicitly names the timing choices (immediately, next billing cycle, end of term), the default (end of current bill cycle), and the edge case where a future-dated subscription is deleted instead. It also distinguishes cancel from terminate and notes the reactivation window, giving the agent clear routing logic.

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