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

Beyond the annotations (readOnly, openWorld, idempotent), the description discloses rich behavioral details: fan-out across external APIs, exact return fields, partial failure degradation, and a 5-30s latency for bundlephobia's first measurement with 'sources_failed' listing timeouts. This fully prepares the agent for realistic behavior and edge cases.

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 a dense paragraph but every sentence contributes: purpose, use cases, return summary, ecosystem limitation, and failure modes. It could be slightly more structured (e.g., bullet points), but it remains readable and front-loaded with the key purpose. Appropriate for a composite tool.

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 (external API fan-out, no output schema), the description is remarkably complete. It lists the exact summary fields, behavior on partial failures, latency expectations, and alternative routing for non-npm ecosystems. An agent has enough context to invoke it correctly and interpret results confidently.

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%, so the baseline is 3. The description adds some context around the 'version' parameter (defaults to latest, returns alternatives) and clarifies the package scope, but most parameter semantics are already captured in the schema's field descriptions. No significant addition beyond what's structured.

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'. It clearly distinguishes itself from siblings by naming the exact external sources (deps.dev, bundlephobia) and the scope (npm ecosystem only). This leaves no ambiguity about the tool's function.

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?

Explicit guidance is given: 'Use whenever an agent asks "is X safe / popular / small" or "what does adding lodash cost me"'. It also states exclusions: 'NPM ecosystem only in v1; PyPI / Maven / Cargo / Go fall under deps.dev:version directly', correctly directing non-npm queries to an alternative.

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