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

The annotations already cover read-only, idempotent, non-destructive, open-world behavior, so the bar is lower. The description still adds real value beyond them: no wallet, no payment, and a sample (not full) response, which is exactly the behavioral context an agent needs before spending USDC.

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 with the [FREE] marker and pricing context front-loaded; every clause earns its place and nothing is repeated from structured fields.

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 zero-parameter inspection tool with no output schema, the description covers cost, payment, and argument expectations. The one meaningful gap is whether the sample payload is static or live data, which would affect how an agent interprets the preview.

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 zero parameters the baseline is 4. The statement 'no arguments needed' is consistent with the empty schema and additionalProperties:false, giving the agent positive confirmation rather than leaving it to infer from an empty properties object.

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 plainly that this is a free preview returning a sample response for the domain_intel tool, which distinguishes it from its paid sibling. The actual domain-specific subject matter (RDAP/DNS email-auth) lives only in the title, but for a preview tool the 'what' is adequately conveyed.

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?

'See the shape before paying 0.012 USDC' gives a clear condition for choosing this over the paid domain_intel, and 'no arguments needed' clarifies invocation. It stops short of explicitly naming domain_intel as the alternative to call once satisfied, but the routing intent is unmistakable.

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