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

Annotations already cover readOnly/idempotent/openWorld/non-destructive, but the description adds material behavior beyond them: $0.001 per-call pricing with 10 free/day and x402 payment-required results, error semantics (isError on invalid input or upstream failure, not charged), upstream data sources, and heuristic flagging of deprecated or stale (2+ years) 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?

Dense but front-loaded and clearly segmented with 'When to use:', 'Price:', and 'Errors:' labels, so the key facts are scannable. It is longer than strictly necessary, but nearly every clause (pricing, error charging, alternative tool) carries information an agent would otherwise guess wrong.

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 an output schema present the return shape needn't be explained, and the description still covers scope, supported registries, cost model, error/charging behavior, and the sibling alternative. Nothing needed to call it correctly is missing.

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 the schema already documents 'name' and the 'ecosystem' enum/default. The description reinforces the supported registries but adds no syntax or format detail beyond the schema, 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?

Names a specific verb+resource (package metadata) and enumerates the exact fields returned: latest version/release date, license, downloads, maintainers, repo, dependency count, deprecation. It also scopes the supported registries (npm, PyPI, crates.io), so an agent can distinguish it from unrelated siblings like github_repo or web_meta.

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?

Contains an explicit 'When to use' clause and names the alternative with the condition that selects it ('for known vulnerabilities in a version use vuln_check'). This is exactly the when-to-use/when-to-use-something-else routing an agent needs.

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