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

The description discloses significant behavior beyond annotations: it fans out across two external services, returns a specific summary block with field names, includes per-advisory details and alternative versions, and explains partial-failure behavior with a concrete timing constraint ('bundlephobia's first measurement can take 5-30s; sources_failed will list it if it times out'). This exceeds the safety hints provided by 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 dense but every sentence earns its place: purpose, usage context, return format, ecosystem scope, and failure-handling are each covered in separate, well-structured sentences. It front-loads the core purpose and avoids fluff. Five sentences is appropriate for a composite tool of this 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 must convey return values, and it does: it lists the summary fields, per-advisory detail, links, and alternative versions. It also covers limitations (NPM-only), timing, and graceful degradation, making it complete for an agent to understand 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 covers both parameters with clear descriptions (package name, version with default behavior), and schema description coverage is 100%. The description adds context around what the tool returns but does not materially enrich the meaning of the parameters beyond what the schema already provides. 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, concrete purpose: 'Composite "should I add this npm package to my project" check in ONE call'. It clearly identifies the resource (npm package) and the action (scan/evaluate), and immediately differentiates itself from siblings by naming the composite data sources (deps.dev, bundlephobia). It also explicitly scopes to 'NPM ecosystem only in v1', making it distinct from broader tools like deep_research.

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 gives explicit usage triggers: 'Use whenever an agent asks "is X safe / popular / small" or "what does adding lodash cost me"'. It also provides a clear exclusion/alternative for non-npm ecosystems ('PyPI / Maven / Cargo / Go fall under deps.dev:version directly'), telling the agent when NOT to use this tool and what to use instead.

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