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

Goes well beyond the readOnly/openWorld annotations by disclosing that dependency metadata is capped, which related data categories are deliberately absent, and two critical operational facts: a $0.01 USDC per-successful-call charge on Base and an x402-capable wallet client requirement. These are exactly the constraints an agent must know before attempting a call.

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?

Three tight sentences: capability and returned fields first, then exclusions, then cost and auth prerequisites. Every clause carries information an agent needs, with no filler or repetition.

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 compensates by naming the returned fields (latest version, license, publication times, dependency metadata) and the deliberate omissions. The payment and wallet prerequisites are also stated, so nothing required to call it successfully is 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?

Schema description coverage is 100%, so both parameters are already fully documented with pattern, default, and maxLength constraints. The description only restates the scoped-name form ('including scoped names') and alludes to the cap ('capped dependency metadata'), adding little beyond the schema; the baseline 3 applies.

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 with scope ('Look up one exact npm package') and enumerates the exact payload returned, so the agent knows precisely what this does. It does not explicitly differentiate itself from the closest sibling, pypi-packages, or other lookup tools, leaving that to the agent's inference from the ecosystem name.

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?

The word 'exact' plus the negative list ('No maintainers, users, contacts, README, tarball or download calls') gives clear when-not context and steers the agent away from expecting those fields. It stops short of naming an alternative tool or stating the condition under which another sibling should be chosen instead.

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