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

Adds real context beyond the annotations: open-world public-registry scope, explicit non-goals, and a pricing model ('$0.002 USDC per successful call') that tells the agent this call has a cost and that billing is success-conditioned. It does not cover rate limits or failure modes. Note a mild tension: readOnlyHint=false sits oddly against a description that reads as a pure lookup, though the paid-call semantics likely explain the annotation.

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?

Front-loaded with the core verb and resource, then the exclusions, then price; every clause carries information. The opening sentence is long and multi-clause, but nothing is padding.

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 carries the return-value burden and does list the reported fields (existence, resolved version, deprecation/yank, license, runtime requirement), which is enough to call it correctly. It could be more explicit about the response shape or what happens on a miss/unknown version.

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, but the description adds meaning the schema does not: it clarifies that a version may be resolved to 'current/latest' when unspecified, which explains the optionality of the version parameter. Ecosystem scoping to npm/PyPI is also reinforced in prose.

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+resource pair ('verify whether a specific npm or PyPI package version exists') and enumerates the exact outputs (existence, current/latest version, deprecation/yank state, license, runtime requirement). It also scopes itself against the sibling family ('public-registry package install preflight') so an agent can place it next to domain_preflight and commerce_availability without ambiguity.

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?

Explicitly frames the intended moment of use ('before installation') and names two exclusions ('does not resolve dependency graphs or perform vulnerability analysis'), which is strong when-not guidance. It stops short of pointing at any concrete alternative tool for those excluded jobs, so it is a 4 rather than a 5.

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