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

Beyond the annotations (readOnly, idempotent), the description discloses important behaviors: it fans out across multiple services, partial failures degrade gracefully, bundlephobia's first measurement can take 5-30s, and sources_failed will identify timeouts. This adds genuine context not available in annotations.

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 longer than two sentences but is well-structured and front-loaded with the core purpose ('Composite... in ONE call'). It includes a detailed list of return fields, which is necessary given no output schema. Each sentence contributes useful information, though it could slightly be more compact.

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 no output schema, the description thoroughly explains return values (summary block fields, per-advisory detail, links, recent alternatives), failure behavior, ecosystem limitations, and potential latency. It is complete for an agent to know what to expect and how to handle edge cases.

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 with descriptions for both parameters. The description does not add the parameter semantics beyond what the schema provides (e.g., default version behavior is already in the schema). Baseline 3 is appropriate as the description adds no extra meaning.

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 evaluating whether to add an npm package, combining data from deps.dev and bundlephobia. It uses specific verbs ('scan', 'check') and explicitly distinguishes itself by the composite nature and NPM-only scope.

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 provides explicit usage triggers: 'Use whenever an agent asks is X safe / popular / small' or 'what does adding lodash cost me'. It also names an alternative for non-NPM ecosystems ('PyPI / Maven / Cargo / Go fall under deps.dev:version directly'), giving clear when-to-use and when-not-to-use guidance.

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