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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered; the description's 'Read-only' merely restates it. However, '1 credit' discloses a per-call cost that annotations cannot convey and that materially affects an agent's budget decisions. It stops short of explaining when credits are charged or whether results are cached/sampled.

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 terse fragments front-load the returned metrics, then cost, then safety - no filler, no padding. The trailing 'Read-only' is redundant with the readOnlyHint annotation and is the one line that does not earn 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 single-purpose, two-parameter metric tool with no output schema, the description does state the shape of the return (the three metrics) and the cost and safety profile. It is nearly sufficient; an explicit note on what DataForSEO rank measures or on failure behavior when a competitor domain is invalid would close the remaining gap.

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%: the schema already explains that 'brand' defaults to the account brand and that 'competitor' is a domain like competitor.com. The description adds nothing about either parameter, so the baseline 3 applies since the schema carries the full burden.

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 names the exact metrics returned (referring domains, backlink count, DataForSEO rank on a 0-1,000 scale), so an agent knows precisely what data this tool delivers. It is a noun phrase rather than a verb+resource, and it offers no explicit differentiation, but no sibling tool overlaps this backlink domain, so ambiguity is low.

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?

There is no statement of when to call this tool versus alternatives, no prerequisite or ordering guidance, and no mention of what kind of task it serves (competitor analysis, SEO audit, etc.). Only the cost note hints at usage trade-offs; the agent must infer the context itself.

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