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

Annotations already cover read-only/idempotent/open-world, so the bar is lower, and the description clears it by adding the payment model that nothing else discloses: paid tool, x402 USDC on Base, $0.002 per successful call, and that an unpaid call returns a PaymentRequired object. That is exactly the kind of operational context an agent needs before invoking.

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-loaded with the usage trigger, followed by the field inventory and the payment caveat. The field enumeration is dense but each entry tells the agent what it will receive, so no sentence is filler.

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?

No output schema exists, so the description carries the return-value burden and does so by listing the artifact fields. Both required parameters are addressed, and the payment/auth flow and dist-tag resolution are covered, leaving nothing an agent needs 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?

With 100% schema coverage the baseline is 3, and the description adds the semantic that passing "latest" performs dist-tag resolution rather than being treated as a literal version string. That is a meaningful behavioral nuance beyond the schema's bare "Exact version or 'latest'".

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 concrete verb (retrieve the exact published artifact) and a precise resource (an npm version), and enumerates what that artifact contains (deps, engines, dist, publish time). This implicitly separates it from package-level siblings like npm_package, but no sibling is named explicitly, so it stops just short of a 5.

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?

"Use when you need the exact published artifact for an npm version" gives a clear triggering context, and the note that "latest" resolves the current dist-tag is actionable guidance. However, it never states when to prefer npm_package or npm_search instead, so there are no explicit exclusions or alternatives.

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