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

Beyond the annotations (readOnly, idempotent, non-destructive), the description discloses partial failure behavior and latency: 'bundlephobia's first measurement on a new version can take 5-30s; sources_failed will list it if it times out, the rest still returns.' It also reveals the fan-out architecture, adding valuable context about how the tool operates.

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 but well-structured, starting with purpose, then usage, return fields, scope, and failure behavior. Every sentence provides value, though the length is slightly above the minimum needed. The use of em-dashes and semicolons improves readability.

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 adequately enumerates the return structure (summary block fields, per-advisory detail, links, recent alternative versions). It also covers ecosystem limitations, partial failure behavior, and latency expectations, making it complete for the tool's 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?

The input schema already provides clear descriptions for both parameters (package name and version with default behavior), covering 100% of the parameters. The description does not add additional meaning to the parameters beyond what the schema states, so 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 the tool is a composite check for 'should I add this npm package to my project', explicitly mentioning the resources (deps.dev and bundlephobia) and the specific data points it returns. It distinguishes itself from siblings by being a one-call composite, rather than a single-source lookup.

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?

Provides explicit usage triggers ('whenever an agent asks 'is X safe / popular / small' or 'what does adding lodash cost me'') and an explicit exclusion with alternative: 'NPM ecosystem only in v1; PyPI / Maven / Cargo / Go fall under deps.dev:version directly.' This is clear when-to-use and when-not-to-use guidance.

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