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 real behavioral context beyond that: the guarantee that it 'never contains exploit code', that EPSS is 'read live from FIRST', that KEV is 'null when checked and absent', and that `unstated` means the task is in the benchmark without a published result. These null/absence semantics are exactly the kind of disclosure annotations cannot express.

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?

The purpose is front-loaded in the first clause, followed by input format then return shape, which is a sensible order. It is dense but nearly every clause carries information the agent needs given the absence of an output schema; only the long field enumeration pushes it toward the verbose side.

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 takes on the burden of describing the return value, and it does so thoroughly: top-level OSV fields, the `database_specific.openvuln` sub-structure (`label`, `fix`, `exploitation`, `subject`, `class`, `sources`), and the meaning of null and `unstated`. Combined with complete id-format guidance, nothing essential is missing for correct invocation.

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% for the single `id` parameter, so a baseline of 3 applies. The description earns more by enumerating eight distinct id namespaces (including MAL and NDB, which the schema's examples do not mention), giving the agent a much clearer picture of valid input than the schema alone.

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 a specific verb+resource combination: retrieve 'everything known about one vulnerability' as an OpenVuln/OSV record. It explicitly constrains the scope to a single record keyed by one id, which cleanly separates it from the sibling lookup tools (airplane, ship, domain, profile), and an agent can tell immediately what it returns.

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?

It provides clear usage context by enumerating the accepted id families (CVE, GHSA, OSV, PYSEC, GO, RUSTSEC, MAL, NDB) with example ids, which tells the agent when this tool applies. It does not name an alternative tool or state when NOT to use it (e.g. for searching by keyword or package), so it falls short of a 5.

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