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

No annotations exist, so the description carries the burden, and it delivers: it discloses the $0.005 USDC cost via x402 on Base (a critical operational trait for an agent deciding whether to invoke a paid tool) and explains that it returns only the deciding facts rather than the registries' hundreds of kilobytes. It does not cover not-found or error behavior, which keeps it below 5.

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?

Four sentences, each earning its place: purpose and output facts, usage timing, behavioral filtering note, and cost. Purpose is front-loaded and there is zero filler.

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?

For a simple 2-parameter lookup with no output schema and no annotations, the description covers what is returned, when to call it, and its cost — the essential operational facts. The main gap is behavior for nonexistent packages or registry errors, but the tool is otherwise fully navigable.

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 100% — both 'name' and 'ecosystem' are already documented with examples and aliases in the schema. The description adds no parameter-level detail beyond mapping the registries to the ecosystem field, so the baseline 3 applies.

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?

States a specific verb and resource ('Look up a package in npm, PyPI or crates.io') and enumerates the exact output facts (latest version, licence, deprecated/yanked status, last published, dependency count, repository). This fact list clearly differentiates it from the sibling package_audit and package_vulnerabilities tools by content, even without naming them.

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?

Provides two concrete use cases: 'Use before writing a dependency line, or to check whether a pinned version is behind.' This gives clear contextual guidance but stops short of naming sibling alternatives or stating when-not-to-use, so it misses the top bar.

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