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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds material context beyond that: the $0.02 USDC charge per call via x402, and the underlying data sources (README and changelog). It does not describe latency, failure modes for unknown/private packages, or output shape, but the cost disclosure is a genuinely important behavioral trait.

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?

It is a single dense sentence, front-loaded with the core value proposition (current docs for stale training) before the enumeration and cost. Every clause carries information, though the sentence is long enough that the cost note could be split out for readability.

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 is not obliged to detail return values, and the readOnly annotation covers safety. It conveys what data is fetched and its source, plus the per-call cost. The remaining gap is behavioral edge cases (unknown package, package not on either registry) and the async flag, minor for a read-only lookup tool.

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 description coverage is only 40% (2 of 5 params described), so the description needs to compensate. It does partially: 'npm or PyPI' clarifies the ecosystem param, 'the version you know' maps to from_version, and 'how to use it now' hints at the question param. But 'async' and the required 'package' format receive no explanation anywhere.

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 states a specific resource (npm or PyPI package docs) and the exact information returned: latest version, current usage, and breaking changes since a known version, sourced from README and changelog. It is far more specific than siblings like package_info or docs_ask, but it never names or contrasts with those overlapping siblings, so an agent must infer the boundary itself.

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 phrase 'for agents with stale training' implies the triggering situation (you need docs newer than your training data), which is useful implicit guidance. However, there is no explicit when-not condition and no named alternative such as package_info for simple metadata or docs_ask for general documentation, leaving usage boundaries to inference.

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