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

Adds real context beyond the annotations: deprecation/advisory severity comes from deps.dev for pinned versions, and "ok means no listed flags, not a safety guarantee" sets expectation limits on the result. It also explains the otherwise puzzling non-idempotent read behavior — each call is billed, failed calls are free, first 25 free — which reconciles with idempotentHint=false.

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 returned signals, then ecosystem coverage, then alternatives, then cost. Nearly every sentence carries distinct information, but the pricing sentence is dense and mixes three separate billing facts, slightly packing the tail.

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 still enumerates the returned fields and the caveat on interpreting them. For a read-only lookup with three simple parameters, nothing an agent needs in order to select or call it correctly 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 coverage is 100%, so the baseline is 3, but the description adds meaning the schema lacks: passing an exact version unlocks pinned-version metadata and switches advisory source to deps.dev. The example (ecosystem=npm, name=lodash) reinforces the naming convention, though version-format edge cases are left to the schema.

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 up front: reports package existence, latest version and release, age, version count, npm weekly downloads, licenses, deprecation and advisory severity. It also enumerates all six supported ecosystems, so an agent knows exactly what the tool covers versus sibling lookups.

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 an explicit use case ("Use before adding a dependency") and names the alternative with the condition that selects it: package_audit for OSV affected ranges and dated EPSS CVE estimates when an exact pinned version matters. The optional version semantics (exact only, no ranges/tags) are also stated.

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