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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so safety is covered. The description adds value beyond them by disclosing the content of the response (plan names, billing periods, prices) and the downstream use of the returned id. Minor gap: no note on whether the list is fixed, localized, or currency-dependent.

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 short sentences with zero filler: the first defines the payload, the second defines the next action. Content is front-loaded and nothing needs to be skimmed for.

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 no output schema, the description carries the burden of describing returns and does so adequately (plans, billing periods, prices), plus the follow-up action. Slightly incomplete in that it doesn't say whether plans vary by region/currency or how many entries to expect.

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 there is nothing for the description to disambiguate. Baseline for a no-param tool applies, and the description correctly describes it as an unfiltered listing rather than implying hidden filtering options.

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?

Specific verb+resource ("List the paid plans") with the returned fields enumerated (Premium, Pro, billing periods, prices), so the agent knows exactly what comes back. It does not explicitly contrast itself with the nearby billing_status sibling, which is the only thing keeping it off a 5.

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?

"Use the id with upgrade_plan" gives a clear downstream workflow and implies this is the pre-upgrade discovery step. However, there is no explicit when-to-use/when-not or a pointer to billing_status for account-level billing questions, so the routing is only implied.

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