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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuine value with the per-call cost ($0.02), which annotations cannot express and which matters for an agent budgeting calls. However it says nothing about latency, caching, failure modes for unknown domains, or freshness of the metrics.

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 short sentences with zero filler, and the core purpose is front-loaded ahead of the cost disclosure. Every clause (metric list, price) conveys distinct information an agent would otherwise lack.

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 no output schema, the description usefully compensates by enumerating the return fields and giving the domain-rank scale (0–1000), plus a cost figure. It is nearly complete for a one-parameter read tool; the remaining gap is that it never clarifies how it relates to referring_domains or whether metrics are cached/as-of a date.

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% for the single required parameter, and the description's phrase 'for a domain' matches the schema's own 'Domain such as example.com' without adding format rules, subdomain handling, or URL-vs-domain behavior. Baseline 3 applies when the schema carries the semantics.

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 resource and scope: backlink totals for a domain, and enumerates the returned metrics (domain rank, backlinks, referring domains, nofollow share, broken backlinks, spam score, first-seen). That is a clear verb-less but unambiguous read purpose. It stops short of distinguishing itself from the sibling referring_domains, which covers overlapping territory.

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?

There is no explicit when-to-use guidance and no mention of alternatives, even though referring_domains and domain_overview are close siblings an agent must choose between. Usage is only implied by the metric list. The cost note hints at a tradeoff but never tells the agent when this is the right pick over a cheaper or more detailed sibling.

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