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

With no annotations, the description carries the full burden. It discloses the cost ($0.09 via x402) and the lookup types, implying a read-only network operation. It does not describe return format, error handling, or rate limits, but the main behavior is clear for such a simple lookup tool.

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?

A single sentence conveys the purpose, cost, and data sources with no unnecessary words. It is front-loaded with the price and clearly structured with a dash separating the title from the details.

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 2-parameter tool with no output schema, the description lists the exact enrichments (RDAP, MX, Wikipedia), states the cost, and identifies the required input domain. It could mention the output format or what happens on invalid domains, but this is sufficient for the tool's simplicity.

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 baseline is 3. The description adds meaningful context by stating the cost and the x402 payment method, which directly relates to the x_payment parameter beyond what the schema says. It does not redundantly repeat schema details.

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 looks up specific data points: company domain registration age (RDAP), DNS MX mail servers, and Wikipedia metadata. The verb 'lookup' is specific and the resource is well-defined. This differentiates it from siblings like wikipedia_lookup or web_search.

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 implies use for B2B lead enrichment by stating 'B2B Domain & Lead Enrichment' and lists the data sources. However, it does not explicitly state when to use this tool over alternatives like web_search or wikipedia_lookup, nor does it mention exclusions or prerequisites beyond payment.

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