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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive, so the safety profile is covered. The description adds genuinely useful behavior: the exact returned fields, the free-call quota (5 per UTC day per IP), the X-API-Key requirement after that, per-call credit cost, and that not_found and fetch_failed are neither charged nor consume a free call. That is above the annotation bar, but it omits response shape details and whether results are cached or versioned.

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?

Front-loads purpose and return fields before billing mechanics, which is the right order. It repeats the full ecosystem list already present in the enum, and the signup URL sentence is promotional rather than functional, but overall it is tight.

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 carries the return-value explanation and does so precisely (advisory id, summary, CVE aliases, severity, fixed versions). Error-state and billing semantics are also covered, leaving nothing an agent needs in order to call this correctly.

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%, and the description largely restates what the schema already documents, including the ecosystem enum and the vendor/package default heuristic. It adds no format or syntax guidance beyond the schema, so the baseline of 3 applies.

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: "Look up known vulnerabilities for one package version from OSV." It also scopes itself with "This is not a full audit." It does not name the sibling check_package or explain how this differs from it, so an agent must infer the boundary.

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?

Gives clear operating context: single package version, empty list means OSV returned nothing, and successful empty lookups are still charged. The lack of explicit comparison against check_package keeps it from a 5.

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