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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint false, so the description's burden is lighter. It adds meaningful behavioral context: the $0.18 per successful call charge and that 4xx/5xx errors are not billed, which informs cost-aware invocation beyond what annotations provide.

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 with no filler. The first sentence leads with the action and enumerates the returned metrics; the second adds the billing caveat. Every clause earns its place.

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 simple read-only, two-parameter lookup with an output schema, the description covers the essentials: the action, parameters, and cost behavior. The 4xx/5xx note partially addresses error responses, though a brief mention of invalid-target behavior would make it fully complete.

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 both required parameters (target, date) are already documented with formats and examples. The description restates 'target domain' and 'given date' but adds no new semantic detail beyond the schema.

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 clearly states 'Return core Site Explorer metrics' for a target domain and enumerates the exact metrics (organic/paid keyword counts, top-3 keyword count, organic traffic, traffic value), making the resource and scope precise. However, it does not explicitly contrast with sibling tools like get_ahrefs_domain_rating, so it falls short of a 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?

No guidance is given about when to choose this tool over alternatives; it doesn't mention any sibling, exclusion criterion, or prerequisite. The only extra context is billing, which is not usage direction, leaving selection to inference.

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