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

Annotations establish the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lowered. The description adds real value beyond them by disclosing the provenance of the data (GitHub-reviewed advisories, OSV MAL) and the critical caveat that absence of a listing is not a safety guarantee.

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?

Three sentences, each earning its place: what is checked, when to use it, and the false-negative caveat. The key action and scope are front-loaded in the first 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?

There is no output schema, so the description carries some burden for explaining results, and it does gesture at outcomes (listed vs. not listed, 'Dangerous: avoid') without detailing the response shape. For a simple two-parameter lookup this is nearly sufficient; only the exact return format is left implicit.

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 only 50%, and package_or_slug has no inline schema description; the description supplies that meaning by stating the value may be an npm/PyPI package name or an Agent Tested slug. The ecosystem param is already documented in the schema as an optional narrowing filter, so it needs no further explanation here.

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 ('Check') and precise resources (npm or PyPI package name, or Agent Tested slug) and names the exact data sources consulted (GitHub-reviewed advisories, OSV MAL records, 'Dangerous: avoid' tools). No sibling does anything similar, so an agent can select it unambiguously.

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?

Gives an explicit trigger: 'Use it before installing an MCP server or agent package.' It also warns about the limits of a negative result ('Not being listed does not prove a package is safe'). It stops short of naming an alternative tool for cases where this check is insufficient, but no sibling overlaps in scope.

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