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

The description adds behavioral insights beyond the annotations: it notes that the tool fans out to multiple sources, that partial failures degrade gracefully, and specifically that bundlephobia's first measurement on a new version can take 5-30s and may cause a timeout that appears in sources_failed while the rest returns. These are not derivable from the readOnly/openWorld/idempotent hints, making the description more transparent.

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 efficiently structured: the first sentence states the composite purpose and sources, the second gives usage triggers, the third describes the return payload, and the final sentence handles ecosystem scope and failure behavior. Each sentence earns its place, and the key 'what is it' is front-loaded.

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?

Given the tool's complexity (multiple remote sources, partial failures, timing) and the absence of an output schema, the description is remarkably complete. It names all output categories (summary block fields, per-advisory detail, links, alternative versions), explains partial failure handling, and clearly states the v1 ecosystem limitation with a pointer to a direct alternative. Nothing critical 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?

The input schema already covers both parameters with clear descriptions (package name, version with default behavior). The description adds no new parameter-level semantics beyond what the schema states, so the baseline of 3 is appropriate. It does not need to compensate for schema coverage because coverage is 100%.

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 purpose: 'should I add this npm package to my project' check in ONE call, which clearly differentiates it from other tools. It names the two data sources (deps.dev and bundlephobia) and the exact dimensions covered (license, advisories, bundle size, etc.), leaving no ambiguity about what the tool does.

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 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 exclusion and alternative: 'NPM ecosystem only in v1; PyPI / Maven / Cargo / Go fall under deps.dev:version directly.' This gives both positive and negative usage guidance with a named alternative.

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