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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered by structured fields. The description adds genuine value on the read side by naming the four data points returned, which compensates for the absence of an output schema. It stops short of describing field types, formats, or edge behavior for accounts without a subscription.

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?

A single colon-led sentence that front-loads what is being fetched and then lists the returned fields. There is no filler and nothing redundant to cut.

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?

Because there is no output schema, the description must carry the return-value burden, and it does so for the key fields. It is slightly incomplete in that it does not state the value shapes (e.g. status enumerations, date format) or what is returned when no subscription exists, but for a simple read-only getter this is close to sufficient.

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?

The tool takes no parameters, so there is nothing for the description to disambiguate and the baseline of 4 applies. The gathered fields describe the response rather than any input semantics.

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 and enumerates exactly what the resource contains: plan, status, period end, cancellation flag. This clearly separates it from siblings like get_usage and list_plans, which cover metered consumption and available plans rather than the account's current subscription.

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?

Usage is only implied: an agent can infer this is the tool for reading the current subscription, and the zero-parameter signature makes the scope unambiguous. However, there is no explicit when/when-not guidance and no routing to related siblings such as list_plans or upgrade, which an agent may need when the user asks about changing plans.

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