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

Beyond the readOnly/idempotent/openWorld annotations, it discloses the private-package limitation, the paywall model ($0.002 USDC on Base x402), and the exact unauthenticated failure mode (call without payment returns a PaymentRequired object). It also notes maintainer emails are stripped and that download counts come from the official downloads API over a last-week window.

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, then the return payload, then constraints and pricing — a logical order with essentially no filler. The enumerated return-field list is long but each item earns its place because no output schema exists.

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 burden fully, listing the fields returned. It also covers the auth/payment flow and the unsupported case, leaving nothing an agent needs in order to call this correctly undocumented.

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 single `name` parameter is fully documented there, including the scoped form. The description's "(scoped or unscoped)" restates rather than extends the schema, so baseline 3 is appropriate.

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 states a specific resource (the public npm registry card for a package) and enumerates exactly what it returns, which cleanly separates it from npm_search and npm_version in practice. It never names a sibling or explicitly contrasts with one, so differentiation is inferential rather than stated.

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 public npm registry card for a package (scoped or unscoped)" gives a clear trigger condition, and "Private packages are not supported" plus the payment note act as when-not constraints. No alternative tool is named for cases like searching or version-specific lookups, so routing is only partially guided.

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