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

Beyond the readOnly/idempotent/non-destructive annotations, the description discloses meaningful operational behavior: it fans out to two external services, returns a composite summary, degrades gracefully on partial failure, mentions the 5-30s potential delay, and explains that `sources_failed` will list timed-out sources. This is rich, honest behavioral context.

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 front-loaded with purpose and all sentences provide distinct value: usage, returned fields, ecosystem limitation, and failure behavior. It is longer than a minimal description, but the extra length is justified by the lack of an output schema and the need to explain the composite tool's edge cases.

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 that this tool has no output schema and is a composite across multiple services, the description is highly complete: it covers input scope, data sources, exact returned fields (summary block, per-advisory detail, links, alternative versions), and operational caveats like slow first measurement and graceful partial failure. An agent has enough to decide when to call it and how to interpret results.

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?

Schema coverage is 100% and both `package` and `version` are already well-described in the schema. The description reinforces the npm scope and composite behavior but adds no substantive parameter-level details beyond what the schema states, so 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 concrete, specific purpose — a composite 'should I add this npm package' check — and names the exact data sources (deps.dev and bundlephobia). It also clearly scopes the tool to NPM, distinguishing it from generic dependency tools and any sibling candidates.

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?

Usage guidance is explicit: 'Use whenever an agent asks "is X safe / popular / small" or "what does adding lodash cost me"'. It also gives an exclusion rule by stating NPM-only v1 and directing non-NPM ecosystems to deps.dev:version, so the agent knows when not to use this tool.

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