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

Annotations already declare readOnly, openWorld, idempotent, and non-destructive. The description adds valuable behavioral context beyond annotations: composite fan-out, graceful degradation of partial failures, bundlephobia's first measurement delay (5-30s), and the sources_failed field. No contradictions with annotations.

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?

The description is dense yet compact, front-loading the core purpose and then providing use cases, output fields, and limitations in a logical order. Every sentence carries useful information without redundancy.

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?

Despite no output schema, the description enumerates the exact summary fields returned (is_latest, license, published_at, advisory_count, bundle_kb_min, bundle_kb_gz, dependency_count, has_esm, tree_shakeable), plus per-advisory detail and alternative versions. It covers ecosystem scope, performance caveats, and failure behavior, making it complete for a composite tool of this complexity.

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 the baseline is 3. The description adds extra meaning: scoped packages are accepted ('@types/node') and version defaults to latest when omitted. It also clarifies the npm-only ecosystem constraint, which is not fully captured by the generic 'npm package name' schema description.

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 opens with a specific composite check: 'should I add this npm package to my project' in one call, then names the fan-out sources (deps.dev, bundlephobia). This clearly identifies the tool's verb, resource, and scope, distinguishing it from all sibling tools.

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?

Explicitly states when to use: 'Use whenever an agent asks "is X safe / popular / small" or "what does adding lodash cost me"'. It also provides a clear alternative for non-NPM ecosystems: 'PyPI / Maven / Cargo / Go fall under deps.dev:version directly'. No ambiguity about when to invoke this tool.

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