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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower; the description still adds real value by disclosing that overview/top_pages/page_keywords hit the provider for fresh data, that only 1 domain is processed per call, and that backlinks returns a cached snapshot unless refresh:true.

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?

Three tight sentences, front-loaded with the core purpose and view enumeration, followed by the two behavioral caveats. No filler, though the view list is largely mirrored by the enum.

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 an output schema present, return values need not be described; the description covers view behavior, freshness semantics, and related tools. It leaves minor gaps on location/language defaults and the siteId prerequisite, but is otherwise complete for correct invocation.

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 coverage is 100%, so the baseline is 3, but the description adds meaning beyond the schema by explaining what each view value does and how refresh interacts with backlinks specifically. It does not clarify languageCode/locationCode defaults beyond the schema text.

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+resource ('Looks up any domain, yours or a competitor's') and enumerates the four views, so the agent knows exactly what the tool returns. It stops short of sharply distinguishing itself from siblings beyond listing 'Related' tools, so 4 rather than 5.

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 clear context: use for domain lookups with one of four view modes, and the refresh semantics for backlinks. It names related tools (research_keywords, get_rankings) but does not say when to prefer those over this one, so no exclusion guidance.

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