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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds genuinely new behavior: concurrent invocations are rejected and return no data, which the agent cannot infer from structured fields. It stops short of detailing rate limits or pricing-source caveats, so not a full 5.

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?

Four short sentences, front-loaded with the core purpose before the routing rule and the concurrency warning. The trailing 'Related:' list adds navigational value without padding the prose.

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?

An output schema exists, so return values (price, registrability) need not be explained here, and the description mentions the price dimension anyway. With safety covered by annotations and the concurrency hazard called out, nothing an agent needs to invoke this correctly is missing.

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% and the single parameter is documented as a full domain with TLD including an example. The description adds only the 'single domain' scoping, not format or syntax detail, so baseline 3 applies.

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 a specific verb and resource ('Confirm a single domain's registrability and price') and explicitly narrows scope to one domain, calling itself 'the definitive availability check for one domain.' This lets an agent separate it from siblings like bulk_available, tld_check, and whois without opening any schema.

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?

Gives an explicit routing rule ('For two or more domains call bulk_available once instead of repeating this tool') plus an operational constraint on call sequencing (one call, wait, then next; parallel calls rejected). Both when-to-use and how-not-to-use are spelled out.

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