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

Annotations already cover the safety profile (readOnlyHint=true, idempotentHint=true, destructiveHint=false), so the bar is lower. The description adds genuine business context beyond annotations — that results are live, owner-held domains with 5-20+ years of age, not registrable names — which is useful. It does not, however, describe result size, pagination, or query-cost behavior.

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?

Two tight sentences carry purpose and differentiator, and a third line names related tools. Every sentence earns its place and the core distinction is front-loaded. Minor deduction only because the 'Related:' fragment is terse and arguably could be folded into usage guidance.

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 14-parameter search tool with 100% schema coverage, rich enums, and an output schema (so return values need no prose), the description is near-complete. It covers the key behavioral differentiator (live owned domains vs free-to-register) and the filter surface. The only gap is explicit invocation guidance against siblings, which affiliations ('Related: expired, whois, dns') only partially fill.

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 description coverage is 100%, so the baseline is 3 and the schema already documents all 14 parameters, several with enums and rich detail (e.g., the keyword's 2-character start-match caveat and the tld_count_min cross-referencing prefix_tld_count). The description itself adds no parameter-level meaning beyond the filters it names, which map to schema fields already.

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+resource ('Search currently registered domains with 5-20+ years of history') and enumerates its filter dimensions (keyword, TLD, age range, length, sale status). The line 'These are live domains owned by someone, not free to register' sharply differentiates it from the 'available' family of siblings and from 'expired'.

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 lists 'Related: expired, whois, dns' and implies a use case (finding aged, registered domains) but never explicitly states when to prefer this tool over those siblings. The contrast with 'not free to register' hints at the available-tools boundary, yet there is no affirmative guidance such as 'use expired for domains that lapsed'.

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