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

Annotations already declare readOnly/openWorld/non-destructive, and the description adds real context beyond them: no API key required, per-IP rate limiting, and a full inventory of what comes back (availability, retail/renewal price, registrar, buyUrl). It also warns against fabricating URLs/prices. Rate-limit specifics are absent, keeping it short of a 5.

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?

Front-loads the two most decision-relevant facts ('PUBLIC, NO API KEY required') before the return inventory and the routing rule. Every sentence carries information; nothing is filler.

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 carries the return-value burden itself and does so thoroughly, enumerating each returned field. For a one-param read tool with annotations covering the safety profile, nothing an agent needs 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?

Only one parameter and schema coverage is 100%, so the schema already documents 'domain' with an example. The description adds no format or syntax guidance beyond that, which is the baseline-3 case for a single fully-documented param.

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 ('check domain availability and price') and explicitly distinguishes itself from the bulk sibling by name. An agent can tell it apart from check_domain, check_domains_public_bulk, and buy_domain without opening a schema.

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?

Gives an explicit imperative ('Use this for EVERY candidate before recommending') and names the alternative for the bulk case ('For bulk checks... use check_domains_public_bulk'). Both when-to-use and when-to-use-something-else are covered.

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