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

The description discloses behavioral traits beyond the annotations: it details the fan-out across external services, partial failure handling ('sources_failed will list it if it times out, the rest still returns'), and the potentially slow first measurement ('bundlephobia's first measurement on a new version can take 5-30s'). This adds valuable context beyond the readOnlyHint and idempotentHint annotations, with no contradictions.

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 structured: purpose, usage trigger, return value breakdown, ecosystem limitations, and failure behavior are all covered in a logical order. No sentence is wasted; each adds critical information for tool selection and invocation. The length is justified by the tool's complexity.

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 carries the full burden of explaining return values, and it does so thoroughly: lists summary block fields, per-advisory details, links, and alternative versions. It also covers edge cases (timeouts, ecosystem limitations) and clear failure semantics. The description is fully self-contained for an agent to use this tool correctly.

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?

Both parameters (package and version) are fully described in the input schema with 100% coverage, including scoped package examples and default-to-latest behavior. The description itself does not add meaningfully to the parameter semantics; it focuses on the composite output rather than the parameters. With schema coverage at 100%, the baseline 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 opens with a specific verb+resource: 'Composite "should I add this npm package to my project" check in ONE call', clearly stating what the tool does and its scope. It distinguishes itself from siblings by naming the exact data sources (deps.dev and bundlephobia) and the composite nature, making its purpose unambiguous.

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"'. Also provides exclusions/alternatives: 'NPM ecosystem only in v1; PyPI / Maven / Cargo / Go fall under deps.dev:version directly', which guides the agent toward the correct tool for non-NPM ecosystems.

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