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

Annotations already declare the safe read-only, idempotent, closed-world profile, so the bar is lower. The description adds real behavioral context beyond them: the results come from a Hivex index (implying staleness/coverage limits), are capped at 25, and each carries a hivex.si page link. It does not note the default status of 'any' meaning results may not be free, which is a minor gap.

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 dense sentences with no filler, front-loading what is searched before the filter options. The option lists are slightly crammed together but every clause carries information.

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 an output schema present, return-value detail is not required, yet the description still notes the 25-result cap and the accompanying page URL. For an 8-parameter, zero-required search tool it is sufficient to call correctly; the main omission is any guidance on the unchecked defaults (limit=10, status='any').

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 only 38%, so the description carries weight – and it does, restating and expanding the fragment match modes (contains/starts with/ends with/exact), the length bound, the minimum score, and the three sort orders. It leaves 'limit' and the default values undocumented, which keeps it short of a 5.

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 gives a specific verb and resource: 'Search Hivex's index of .si domain names that are free to register,' which is unambiguous. It does not, however, differentiate itself from the only sibling, check_name, so an agent cannot tell from the description alone when to search the index versus checking one name.

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?

Usage is implied by the enumerated capabilities (filter by fragment with contains/starts/ends/exact, length, score; sort by best/newest/shortest), which tells an agent what the tool is useful for. There is no explicit 'when to use this vs check_name' guidance and no statement of prerequisites or exclusions.

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