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

The annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the description doesn't need to restate that. It adds genuinely useful context the annotations lack: that each call consumes API credits, plus the shape of the result set (one backlink per domain). It could go further on rate limits or failure behavior for invalid targets, which keeps it from a 5.

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?

A single front-loaded sentence naming the tool, then the returned metrics, then the cost caveat—no filler. The metric enumeration is slightly redundant given an output schema exists, which costs it a perfect score, but nothing here is wasted.

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-parameter, non-destructive read tool with full schema coverage, rich annotations, and an output schema, the description covers purpose, input scope, and the cost side effect—enough to call it correctly. The one material gap is sibling disambiguation: an agent could reasonably confuse this with get_referring_domains or get_backlink_anchors.

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%—both 'target' (domain or full page URL) and 'limit' (1–100, default 25) are fully documented in the schema. The description only echoes the domain-or-URL input scope and adds nothing about the limit parameter or the tradeoff of raising it. Baseline 3 is appropriate when the schema carries the parameter 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?

States a concrete verb+resource ('Backlink checker') and enumerates exactly what comes back: total backlinks, referring domains, domain rank, spam score, and top backlinks one per domain. That is far more specific than a restated title. It stops short of a 5 because it never distinguishes itself from the sibling tools, and listing 'referring domains' as one of its outputs overlaps with the get_referring_domains sibling.

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?

'For any domain or URL' implies the input scope and 'costs API credits per call' signals a budget consideration, which nudges usage. However, there is no explicit when-to-use or when-not-to-use guidance, and nothing tells the agent whether to call this or the sibling get_referring_domains / get_backlink_anchors for a given question—which is a real risk given the output overlap.

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