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

With no annotations, the description carries the full burden and discharges it: it discloses the deterministic outcome (always returns PAYMENT_DISABLED) rather than the general behavior an agent would infer from the name. It also explains why the alternative is preferable (free, one month added), which is exactly the behavioral context needed to avoid a wasted call.

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 sentences, no waste, and the blocking constraint (payment disabled) is front-loaded ahead of the redirect to renew_subdomain.

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 tool whose only meaningful behavior is a guaranteed failure, the description is complete: it tells the agent what happens, why, and what to call instead. With full schema coverage and no output schema, nothing an agent needs to call or avoid calling this tool 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?

Schema description coverage is 100%, including detailed notes on payment and owner_token, so the schema already does the heavy lifting. The description adds no parameter-level meaning beyond alluding to payment being disabled, which warrants the baseline 3.

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 conveys that this tool extends a subdomain by paying for a year ('Paying for a year is switched off'), and explicitly distinguishes itself from the sibling renew_subdomain. It never states the purpose in a clean verb+resource sentence, but the implication is unambiguous and routing to the alternative is explicit.

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?

It states the exact condition under which this tool would be used (paying for a year), declares that this server disables it, and names the alternative (renew_subdomain) with the reason to prefer it ('free and adds a month'). Nothing is left to inference.

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