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

Annotations already cover read-only, open-world and non-destructive behavior; the description adds genuinely new context: the cost model ($0.01/call, first 25 free, failed calls free) and the reason repeats are not free, which explains the non-idempotent hint. It does not describe the shape of the returned counts, but no output schema exists to cover that either.

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 purpose and source, then use case, then cost. Dense but no wasted sentence; the 'reads or computes only and changes nothing' clause is partly redundant with readOnlyHint but short.

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?

For a one-parameter read-only lookup, the definition covers purpose, source, cost and usage. The main missing piece is a hint about the return structure (per-period counts), which matters since there is no output schema.

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 'package' parameter already documents scoped names ('@scope/name'). The description's 'package=hono' example duplicates rather than extends that, 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?

States a specific verb and resource — download counts of an npm package over day/week/month from the official npm registry API — and the sibling set (pypi for Python) makes the npm scope meaningful. An agent can tell exactly what it retrieves without opening the 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?

Gives a clear use case ('judge how widely a dependency is used') and names the data source, but does not state when not to use it or point at alternatives like pypi for Python packages. Clear context with no explicit exclusions.

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