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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive, so safety is covered. The description adds genuinely non-obvious behavior: de-duplication by host, exclusion of the competitor's own domain, and the fact that results are approximate rather than an exhaustive index. It does not describe cost, rate limits, or the shape of returned sources.

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 short sentences, front-loaded with purpose, then the de-dup/exclusion behavior, then the honesty caveat. No filler and nothing restated from the schema or annotations.

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 two-param, read-only, open-world search tool with full schema coverage and annotations, the description covers method, scoping, and reliability expectations. The main residual gap is what the response actually contains (list of source URLs/hosts, mention counts?) since there is no output schema, but the agent can still invoke it correctly.

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%, so both parameters (competitorUrl with accepted URL/domain forms, limit with 1-40 bounds and default 20) are already fully documented. The description adds no extra syntax, defaults, or edge cases beyond the schema, so the 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?

Specific verb+resource: 'Approximate the pages linking to a competitor.' The method (free web-search signals, domain/brand mentions) and the scope (pages linking to a competitor) are both stated, so an agent can distinguish this from verify_page_links or find_mentions. It stops short of naming any sibling explicitly, which keeps it at 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?

Provides clear context for use: a 'free, directional starting point for prospecting,' and warns it is 'not a complete backlink index.' This tells the agent when the tool is appropriate (early-stage prospecting) and its limits. It never names an alternative tool to use when a complete/verified backlink set is needed, so no explicit when-not routing.

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