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

Annotations already establish readOnly, idempotent, non-destructive and open-world behavior, so the bar is lower. The description adds real value beyond them by disclosing the return payload traits (source failures, quote timestamps, minimum terms) and the important limitation that availability is not verified - context an agent would otherwise have to learn the hard way.

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 padding. The scope statement is front-loaded and the caveat about availability is placed immediately after, which is exactly where an agent needs it.

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 13-parameter, output-schema-less read tool, the definition is largely sufficient: safety is covered by annotations, parameters by a fully documented schema, and return shape traits are named in the description. It falls just short of 5 because it never routes the agent away from the overlapping search_prices sibling.

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% with 13 well-annotated parameters, so the schema carries the semantics. The description adds no parameter-level meaning beyond what the schema already provides, 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 verb+resource+scope: 'Compare all covered registrars for one extension.' That is clear and actionable. It does not, however, distinguish itself from the sibling search_prices tool, so an agent cannot tell from the description alone which of the two price tools is the right one.

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 implies usage ('one extension', 'compare all covered registrars') and adds one genuine exclusion - availability is not checked, so check_availability must be used separately. But it never names sibling alternatives such as search_prices or check_availability, nor states when this tool is preferred over them; guidance is only implied.

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