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

Annotations already declare readOnlyHint and openWorldHint, but the description adds meaningful behavior beyond them: up to 20 advisories are listed while 'the count is the full number' (truncation semantics), and the pricing model ($0.002 per successful call via x402, failed calls not charged). That pricing and truncation detail is genuinely useful and not captured in structured fields.

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 sentences, front-loaded with purpose, followed by output shape and pricing. Each sentence carries distinct information with no obvious filler, though the output-format sentence is partly redundant given the output schema exists.

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 an output schema present, return values need not be explained, and the safety profile is covered by readOnlyHint/openWorldHint. The description nonetheless closes the main gaps an agent would care about: truncation behavior and the paid-call cost model. Nothing critical is missing.

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 all three parameters are already documented in the schema and the baseline is 3. The description restates the ecosystem list but adds no format hints (e.g. version string expectations) beyond what the schema's 'Exact version, e.g. 4.17.20' already provides.

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 resource and scope ('Known vulnerabilities of one package version in the OSV database') with the supported ecosystems enumerated. It is clearly distinguishable from siblings like package or package_search by being vulnerability-focused, though it never names an alternative to route between them.

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?

The description implies usage by requiring 'one package version' and listing valid ecosystems, so an agent can infer the required inputs. However, there is no explicit when-to-use vs when-not guidance and no mention of the related package/audit siblings, leaving routing to inference.

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