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

With no annotations provided, the description carries the full burden of behavioral disclosure. It clearly states that this is a 'curated metadata' lookup, implying a static dataset and no side effects. It also explicitly excludes domain registration checks and DNS/WHOIS resolution, which helps set expectations. However, it does not mention error handling for invalid TLDs or whether TLDs with a leading dot are accepted, leaving minor gaps in transparency.

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 concise and well-structured, with a brief opening sentence, followed by 'Use when' and 'Do not use when' sections. Every sentence adds value, providing either core purpose, usage examples, or exclusions. No redundant or filler content exists, making it highly efficient for an agent to parse.

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 simple single-parameter lookup tool with no output schema, the description is complete. It defines the tool's purpose, gives clear usage examples, and lists exclusions, all in a compact format. The lack of output format details is acceptable given the simplicity of the tool and the clarity of its intended use.

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?

The input schema only defines a 'tld' string with minLength 2 and no description (0% schema coverage). The description compensates by providing examples like 'com, io, or ai' and using the phrase 'DNS top-level domain', which clarifies the expected format (no leading dot, not a full domain name). This adds useful semantic meaning beyond the bare schema, though it could be more explicit about punctuation.

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 clearly states the tool's function: 'Identify what a DNS top-level domain such as com, io, or ai is classified as and commonly used for.' This is a specific verb ('identify') plus a well-defined resource ('DNS top-level domain'). It also distinguishes itself from siblings by explicitly stating not to use it for MIME type lookups, which are handled by another tool.

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?

The description provides explicit 'Use when' and 'Do not use when' sections with concrete example queries, such as 'What kind of TLD is .io?' and 'Look up MIME types for file extensions (use mime_lookup)'. This gives clear guidance on when to use this tool versus alternatives, making it easy for an agent to route correctly.

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