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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds substantial context beyond them: a per-call price ($0.005 USDC), the payment protocol (x402 v2 on Base), the required PAYMENT-SIGNATURE header, and the direct endpoint URL. Auth/payment requirements of this kind are exactly what 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?

Front-loads the highest-value information — what it returns and the cheapest-tier positioning — before the payment mechanics. Dense and somewhat run-on in the final sentence, but essentially every clause carries distinct information.

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 correctly enumerates the returned fields, and it supplies pricing, transport, and the sibling alternative. Remaining gaps are minor: error behavior, rate limits, and any latency/pagination expectations for a paid call are unstated.

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 0%, so the description must carry the burden. It enumerates the three inputs and notes that version is optional and that ecosystem takes npm or PyPI, but the enum and optionality are already in the schema, and it adds no format guidance for name (e.g. scoped packages) or version strings.

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 (package metadata retrieval) and enumerates exactly what is returned: latest/resolved version, license, publish dates, downloads, deprecation, install scripts, maintainer count. It explicitly distinguishes itself from the sibling pkg-check, so an agent can route without opening either 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?

Names the alternative ('No vulnerability scan (see pkg-check for the full safe/caution/avoid verdict)') and positions itself as the 'cheapest tier', which is a clear usage signal. However, it is silent on the other overlapping sibling, qc_licence, despite this tool returning license data — leaving a routing ambiguity unresolved.

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