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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds a real behavioral trait beyond that: null results are returned for unknown multi-year term totals, which tells the caller how to interpret an empty-looking response. That is meaningful added context, though nothing is said about rate limits or coverage limits beyond the TLD constraint.

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 filler. The core computation is front-loaded and the two exclusions and the null-return caveat follow in a single tight sentence. Every clause earns its place.

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?

There is no output schema, so the description must carry return semantics; it does partially by explaining the null case. For a read-only, idempotent estimate tool with fully documented parameters this is close to sufficient, though it doesn't describe the shape of a successful cost response.

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% and each parameter is documented in the schema itself (tld pattern/coverage, years horizon, registrar ID source). The description's 'one TLD' and 'multi-year term totals' echo the schema without adding syntax, format, or defaults beyond it, so the baseline of 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 computed output: new registration plus subsequent renewals for one TLD at a registrar. It also scopes out transfer and existing-domain renewal, which an agent can use to orient. It does not name the nearest sibling (get_tld_prices / search_prices), so a full 5 for sibling differentiation is not warranted.

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?

The description says what this is not (transfer quote, existing-domain renewal), which is useful negative guidance, but it never states when to prefer it over get_tld_prices or search_prices, nor any prerequisite such as needing a connected registrar ID (that lives only in the schema). Usage is implied rather than directed.

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