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

Annotations already cover readOnlyHint and destructiveHint, so safety is clear. The description adds behavioral value by disclosing that it returns exact registration and expiry timestamps, splits names into words, and that names usually appear within minutes of registration (real-time feed). It hints at pagination limits via 'deeper paging' reference, though the exact 10000 limit is only in the schema.

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 compact—two short paragraphs. The first sentence immediately states purpose, followed by key outputs and timing. The second paragraph gives routing guidance without fluff. No redundant or irrelevant sentences.

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 10 optional parameters and an output schema present, the description covers purpose, scope, real-time behavior, and explicitly mentions alternatives for limitations. The 10000-page limit is only in the schema, but the 'deeper paging' comment implies it. Overall, the description is adequate for an agent to decide when to use it and what it does.

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 covers all 10 parameters with descriptions (100% coverage), so baseline is 3. The main description adds no extra parameter-specific meaning; it provides context about TLD scope and time window, but that doesn't augment the semantics of individual parameters beyond what the schema already states.

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 states a specific verb (Search) and resource (domains), with a clear time window (last three days) and scope (all TLDs, including ccTLDs like .ai and .io). It explicitly differentiates from the sibling nrds by noting that nrds handles history beyond three days, making the purpose unambiguous.

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?

It explicitly lists conditions for using nrds instead: history beyond three days, registration-term or for-sale filters, cross-TLD count, or deeper paging. It also explains that nrds carries most recent names but with day-level dates and gTLD focus, giving clear guidance on when to choose an alternative.

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