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

Annotations already declare readOnly/idempotent/openWorld, and the description adds substantial behavior beyond them: per-call price ($0.001), 10 free calls/day with an x402 payment-required result afterward, and error semantics (isError on invalid input or upstream failure, not charged). It also discloses data provenance (registries plus npm/pypistats counts) and the deprecation heuristic (no release in 2+ years).

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 what is returned, then usage routing, then cost and error contract — a sound order with little waste. It is dense rather than padded, though the long comma-separated field list and the parenthetical source note could be tightened slightly.

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?

Output schema exists, so return shape need not be explained; the description still covers the dimension an agent cannot see elsewhere — cost, paywall behavior, and error/charging semantics. Nothing needed to call this 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% and the enum for ecosystem is documented, so the schema already carries parameter meaning. The description reinforces that the lookup spans three registries but adds no syntax or format detail beyond what the schema states; 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 resource (npm/PyPI/crates.io packages) and enumerates exactly what is returned: latest version, release date, license, downloads, maintainers, repo, dependency count, deprecation. An agent can distinguish this from every sibling (arxiv_search, github_repo, web_meta) without opening the schema.

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?

Explicit 'When to use: For package metadata' plus a named alternative and the exact condition that selects it ('for known vulnerabilities in a version use vuln_check', with server and URL). It also states the fitting scenario 'to pick or vet a dependency', leaving no inference required.

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