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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds real context beyond them: results come from the external packagephobia.com service, units are bytes, and install size includes dependencies - but it says nothing about failure behavior for unknown/unpublished packages or latency of the external lookup.

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?

One dense sentence with no filler; the returned values are front-loaded before the input description. It is tightly packed but still readable, with no redundant sentences to cut.

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 only two well-documented parameters, full annotations and an output schema, the description covers what an agent needs to select and call the tool. The only meaningful omission is behavior when the external service returns no data, which keeps it short of full completeness.

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%, with 'npm package name (scoped allowed)' and 'Specific version (default latest)' already documented, so the schema carries the semantic load. The description only restates that version is optional and that scoping is allowed, adding no extra syntax or format guidance beyond the structured fields.

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 ('Return the publish size and full install size ... for an npm package name') plus the distinguishing detail that install size includes dependencies and is reported in bytes. An agent can tell immediately what this tool produces, and no sibling in the catalog overlaps with it.

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 use case (checking an npm package's footprint, including dependency weight) is implied clearly by the output described, but there is no explicit when-to-use or when-not guidance and no named alternative. Acceptable for a narrow single-purpose utility, but it leaves routing to inference.

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