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

Beyond the annotations (which only say non-read-only, open-world, non-destructive), the description adds real operational context: a cost ceiling of 1.6 credits, a caching window ('free for a day'), a data-provenance caveat ('DataForSEO's crawl, not Google's'), and a filtering behavior ('spammy ones left out'). It does not address why readOnlyHint is false for what reads as a pure query, which is the one unresolved behavioral question.

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?

Four dense sentences with no filler; what the tool returns is front-loaded before the usage advice. The opening sentence is long and packs both views plus their returned fields, which is slightly heavy but justified by the amount of distinct information conveyed.

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 does the work of naming the returned fields and the two result shapes, which is enough for an agent to select and call it. Remaining gaps are minor: response envelope/pagination, and the mismatch between a query tool and readOnlyHint=false is not addressed.

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; the description earns above that by giving the view enum operational meaning (referring_domains excludes spammy domains, top_pages surfaces the most-linked pages) and by restating domain defaulting to the project's site. It still leaves limit/pagination semantics entirely to 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 opens with a specific verb+resource ('Backlinks of the project's site or any other domain') and then enumerates exactly what comes back: domain rating, backlink and referring-domain counts, plus either the linking domains or the site's most-linked pages. The two view modes are named inline, so an agent can distinguish this from any sibling without consulting the schema.

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?

It explicitly prescribes the two use cases: 'Use referring_domains on a competitor to find sites that link in this market, and top_pages on the project's site to find the strong pages to link from.' That is a direct when-to-use-which-view rule with no inference required, and the domain/project_id defaulting is reinforced in context.

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