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

Annotations already establish readOnly, idempotent, and non-destructive, so the safety profile is covered. The description adds meaningful behavior beyond that: the Customer Portal link is null when the agent's access does not include billing, which discloses a conditional permission-scoped result. With no output schema, this field list also serves as the return-value contract, adding real value.

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 sentence that front-loads the most important returned field (current plan) and packs the remaining outputs plus the null-condition caveat without any 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 parameterless read-only tool with no output schema, the description does the job of documenting the return payload and the conditional-null case. It does not cover things like caching, rate limits, or error behavior, but nothing essential for correct invocation is missing.

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 zero parameters, so the baseline is 4. There are no arguments whose semantics need explaining.

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 enumerates exactly what the tool surfaces: current plan, renewal/expiry date, plan prices, and a Customer Portal link. Combined with the name and title it is unambiguous, though it never states an explicit verb or differentiates itself from siblings beyond the domain being billing rather than calendars or agents.

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?

There is no indication of when to call this versus alternatives, nor any prerequisites or triggering conditions. With zero parameters the decision surface is small, but the description offers no usage context at all.

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