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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely new context: the fact is free (cost contrast against the paid sibling) and the response carries a primary source, verification status and timestamp — useful for judging trustworthiness of the returned fact.

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 with zero filler: purpose first, return contents second, routing to the sibling last. Nothing is repeated 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?

No output schema exists, so the description carries the burden of describing returns, and it does so at a high level (source, verification status, timestamp). For a one-parameter read tool that is close to sufficient; it omits the ID-miss behavior and any note on response shape, which is what keeps it below a 5.

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?

There is a single required parameter and the schema already documents it at 100% coverage, including the canonical ID pattern, an example ('npm/react/latest-version') and a length cap. The description's 'canonical ID' phrasing is consistent but adds nothing the schema lacks; with one fully documented parameter the baseline of 3 applies, not higher.

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 specific verb and resource ('Read one free published software fact by canonical ID') and names the exact thing it is not ('xguard.web.fetch for a separate paid fetch'). An agent can distinguish it from siblings without opening 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?

Explicitly names the alternative tool and the axis that separates them: free fact lookup versus paid public-URL fetch. It does not cover failure cases (unknown ID, verification failed) or when to reach for xguard.preflight instead, so it stops short of full when/when-not guidance.

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