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

Annotations cover the safety profile (readOnlyHint, openWorldHint), so the bar is lower, and the description still adds genuinely useful behavioral context: it discloses cost ($0.002 USDC per successful call, paid via x402 on named chains) and that failed calls are not charged. That billing/charge-failure semantics is not derivable from annotations or schema. It stops short of describing pagination, latency, or error modes for missing packages.

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 value proposition is front-loaded in the first sentence, with pricing in a separate trailing sentence. The field list is long but each item earns its place by describing returned facts. Only mild density cost from packing all fields into one run-on sentence.

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 two-parameter lookup with a defined output schema and read-only/open-world annotations, this is nearly complete: it covers scope, ecosystems, returned fields, and payment behavior. Missing only the explicit handoff to package_search for name discovery and any note on missing-package behavior.

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%, so both parameters are already documented and the baseline is 3. The enumerated data fields describe the response, not the parameters; the description adds no syntax, casing, or scoping detail beyond what the schema already says for name and ecosystem.

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 names a concrete resource (a package) across three named ecosystems and enumerates exactly what facts are returned (latest version/date, license, repo, maintainers, weekly downloads, deprecation/yank flag, vulnerability count). That is far more specific than a title restatement. It does not, however, explicitly distinguish itself from the sibling package_search, leaving the search-vs-lookup boundary implicit.

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?

Usage is only implied: an agent can infer this is a direct lookup by exact package name plus ecosystem, while package_search is presumably for discovery. The description never states when to prefer this over package_search or what preconditions exist (e.g., exact-name match required), so the agent must infer the routing.

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