check_domain

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

With no annotations provided, the description fully discloses safety and behavior: it mentions cross-checking against three independent signals, explains the 'uncertain' verdict (treated as unknown/NOT available), and notes that price may be absent. This is high-quality behavioral context beyond a simple 'returns availability.'

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?

The description is information-dense yet well-structured, leading with the primary action and then systematically covering scope, alternatives, return values, and edge-case behavior. Every sentence contributes meaning; no 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?

With no output schema, the description correctly enumerates return values: availability verdict, cheapest registrar with buy link, first-year price, and registration year for taken names. It also covers the uncertain edge case, making the tool fully comprehensible for an agent.

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% with a clear parameter description, but the description adds valuable semantics: it clarifies input must be a fully-qualified domain, URLs and 'www.' are stripped automatically, and bare words are rejected (leading to search_domains). This goes well 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?

The description opens with a specific verb and resource: 'Check if ONE specific domain ... is registrable right now.' It clearly distinguishes itself from sibling search_domains by stating it's for a single fully-qualified name. This leaves no ambiguity about the tool's core function.

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?

Explicitly states when to use this tool ('for a single fully-qualified name') and provides a direct alternative ('to test one word across many extensions, use search_domains instead'). It also advises how to interpret 'uncertain' results, adding practical usage guidance.

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