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

Annotations already indicate read-only, idempotent, non-destructive behavior. The description goes beyond by explaining the composite fan-out, the exact output fields, the 5-30s first-measurement delay, and the sources_failed degradation behavior. This adds substantial behavioral context without contradicting the 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 long but well-structured: composite purpose, use cases, return summary, scope limitation, and failure behavior. Each sentence carries necessary information for a composite tool, though it could be slightly more concise without losing value.

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 thoroughly documents all key return fields, per-advisory details, links, and alternative versions. It also covers ecosystem limitations and partial failure behavior, making the tool sufficiently complete for an agent to use without additional context.

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?

The input schema already provides full descriptions for both parameters (package name, scoped packages, version default). The description does not add new semantic meaning beyond the schema, so with 100% schema coverage the baseline score of 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?

The description clearly states a composite 'should I add this npm package to my project' check, naming specific resources (deps.dev and bundlephobia) and the decision it serves. It distinctly positions itself from siblings by focusing on npm packages and aggregating multiple data sources.

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 instructs when to use ('Use whenever an agent asks...') with concrete examples ('is X safe / popular / small'), and provides exclusions ('NPM ecosystem only in v1; PyPI / Maven / Cargo / Go fall under deps.dev:version directly'). Also sets expectations for partial failures and timing, guiding appropriate invocation.

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