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

Annotations only cover the read-only/idempotent/open-world profile; the description goes further by disclosing the upstream source (OSV.dev and its aggregations), the pricing model ($0.002/call, 10 free/day, x402 payment-required result), and error semantics (isError, invalid input or upstream failure not charged). That is exactly the operational context annotations cannot carry.

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?

Purpose and ecosystems lead, then bulk usage, then the when-to-use rule, then pricing and errors — a sensible front-loading of decision-critical info. It is dense but each clause carries weight; only the ecosystem list is mildly redundant with the schema.

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?

An output schema exists, so return values needn't be re-explained, yet the description still names the key return fields. Coverage of pricing, sources, limits, and failure modes leaves nothing an agent needs missing before invoking it.

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% and the schema already lists ecosystems, examples, the 50-item cap, and the "ecosystem:name@version" string format, so the description largely restates it. It adds only marginal meaning (the lockfile-audit framing) and does not clarify how the single-package name/version params interact with the packages array.

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?

Names a specific verb and resource (known vulnerabilities for a package version), lists supported ecosystems, and enumerates the returned fields (severity, CVE/GHSA ids, fixing version). It explicitly distinguishes itself from package_info, so an agent can route between facts and CVEs unambiguously.

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?

"When to use: For CVEs in one package version; for general package facts use package_info" names both the trigger condition and the alternative, including the server where that alternative lives. The bulk-audit case (up to 50 packages to audit a lockfile) is also spelled out.

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