Check Domain

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

Annotations already declare readOnly/idempotent/openWorld/non-destructive, so the safety bar is low, yet the description adds real behavioral context beyond them: concrete rate limits (10 checks/10s here vs 200/min on check_domains), the rationale (Porkbun chunks per registry, batching is cheaper), currency (USD), and a hard downstream constraint that register_domain rejects a mismatched `cost_cents`. None of that is derivable from the structured fields.

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 purpose and return values, then the cost-match warning, then the sibling routing. Every sentence carries actionable weight — the return-field list, the USD note, the register_domain constraint, and the budget rationale each earn their 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?

No output schema exists, and the description compensates by enumerating the return fields (availability, registration/renewal/transfer price, premium pricing details) and currency. For a single-parameter read tool, an agent has everything needed to call it and interpret the result.

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?

With one parameter at 100% schema coverage, the schema already documents the FQDN format and example, so the baseline is 3. The description reinforces the single-domain scope ('a single domain', 'Checking more than one name?'), which is useful but does not add syntax or format detail beyond the schema.

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 (check availability) plus resource (a single domain) and even names the sibling it must not be confused with: 'Checking more than one name? Use `check_domains` instead'. The agent can distinguish check_domain from check_domains, get_pricing, and preflight_domain without opening any 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 prerequisite ('Use this BEFORE register_domain to confirm cost'), an explicit exclusion, and an explicit alternative with the condition that selects it (batch of up to 25 names → check_domains). Nothing about when-to-use or when-not-to-use is left to inference.

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