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

Annotations already declare read-only, idempotent, and non-destructive behavior. The description adds valuable behavioral details beyond annotations, such as the composite nature, potential timeout (5-30s) for bundlephobia's first measurement, and graceful degradation with sources_failed field. This gives agents full awareness of performance and failure modes.

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 relatively long but well-structured: a high-level summary first, then details on data sources, return values, usage conditions, and limitations. Every sentence provides necessary information. It could be slightly more concise, but it avoids redundancy and earns its length.

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 having no output schema, the description comprehensively lists return fields (summary block with specific keys, per-advisory detail, links, alternative versions) and explains edge cases (partial failures, timeout). This gives the agent full understanding of what to expect, meeting all contextual needs.

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 has 100% coverage for both parameters. The description adds semantic value by clarifying that scoped packages like '@types/node' are accepted for the 'package' parameter, and explicitly states that 'version' defaults to the latest published version. This goes beyond the schema descriptions and aids correct invocation.

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's purpose: a composite check for deciding whether to add an npm package, covering license, advisories, bundle size, and more. It uses specific verbs like 'fans out across' and lists data sources, distinguishing it from any sibling tools by focusing on npm dependency evaluation.

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?

The description explicitly says when to use: 'whenever an agent asks "is X safe / popular / small" or "what does adding lodash cost me"'. It also specifies limitations: 'NPM ecosystem only in v1' and directs to alternative tools for other ecosystems. Partial failure handling is also explained, making usage conditions crystal clear.

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