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

Annotations already declare readOnly/openWorld/non-idempotent, and the description adds genuinely new context: the data source (registry RDAP, DNS as fallback), what a 'taken' result contains, and a cost model ($0.01/call via x402 or card key, first 25 free, failed calls free). The line 'each call is charged, so repeats are not free' directly reinforces and explains the idempotentHint=false annotation rather than contradicting it.

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-loaded with the core question and the batch capability, then layers outcomes, use cases, caveats, example and pricing. Dense but essentially paragraph-shaped; the pricing/billing tail could be tightened, but no sentence is pure 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?

For a two-parameter, read-only lookup with no output schema, the description covers what is checked, where data comes from, what each result state means, limits on batching, and cost. An agent has everything needed to decide to call it and how to interpret the 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 coverage is 100%, so the baseline is 3, but the description adds a constraint not present in the schema: a maximum of 20 TLDs per call, plus the clarification that the name may omit a TLD. The worked example (name=agentdatatools) shows intended usage concretely.

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?

Opens with a specific question ('Is a domain name free?') and then states the concrete operation: check one name across up to 20 TLDs against each registry's RDAP server, with DNS fallback. The three possible outcomes (available, taken with registrar/creation/expiry, likely available) make it unmistakably distinct from siblings like domain_report, dns_lookup or domain.

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 explicit when-to-use context ('pick a product or company name, or check a brand before launch') and a clarifying caveat that availability is not a price quote because premium and reserved names exist. It doesn't name an alternative sibling (e.g. domain_report or dns_lookup) or state when not to use it, so it falls short of full routing guidance.

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