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

The description adds significant behavioral context beyond the annotations: billing at $0.36 per row, a 20-row limit, non-charging of 4xx/5xx errors, and semicolon-delimited response format. This covers cost, error handling, and output structure, which the annotations (readOnly, openWorld, idempotent) do not address. No contradiction with annotations.

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?

The description is two sentences: the first states purpose concisely, and the second front-loads billing and response format. Every word earns its place; there is no fluff or repetition. It is well-structured for quick agent parsing.

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?

Given the presence of an output schema, return values are covered. The description adds billing, row limits, error handling, and response format, which are essential for correct invocation. However, it lacks any mention of when to prefer this over siblings, and it doesn't note any prerequisites (e.g., API key or target validation). Still, for a read-only data fetch, it is largely 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?

The input schema already provides 100% coverage for both parameters (target and target_type) with examples and descriptions. The tool description adds no additional parameter-specific semantics beyond restating 'target' generically. Per the baseline rule, 3 is appropriate when schema fully documents parameters.

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 clear verb and resource: 'Referring domains linking to a target, aggregated by domain.' It specifies the aggregation level, distinguishing it from other backlink tools that might list individual backlinks. However, it doesn't explicitly name any sibling tool for differentiation, so it's clear but not maximally distinguishing.

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 provides no guidance on when to use this tool versus alternatives like get_semrush_backlinks_overview or post_dataforseo_backlinks_referring_domains_live. It only describes what it does, leaving the agent to infer context from the name and sibling list. No exclusions or alternative recommendations are given.

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