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

Annotations already cover read-only, idempotent, open-world and non-destructive semantics, so the description only needs to add beyond that. It does: the npm/PyPI not-found behavior (found: false, vulnerable: null, never a clean result) is a genuinely useful edge case that prevents a false-negative read. No return-shape or rate-limit detail, so not a 5.

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, front-loaded with the core action and scope, then the edge case, then the sibling routing. Every sentence carries load and nothing is padded.

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 does explain the key return fields (found, vulnerable) for the negative case, which is the highest-risk ambiguity. It stops short of describing the general response shape or severity fields, but the critical semantics are covered.

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 package, version and ecosystem. The description's 'optionally a specific version' and ecosystem list duplicate what the schema states rather than adding format or syntax guidance, 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?

States a specific verb (checks) and resource (a package, optionally a version) and names the exact data source (OSV.dev) plus the eight supported ecosystems. It is clearly distinguishable from the sibling check tools without opening a 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?

Explicitly routes the agent: use cve_lookup when a CVE/GHSA ID is already known, and supply_chain_check for a combined verdict. It also gives a when-not condition via the nonexistent-package behavior for npm/PyPI, so the agent knows not to read a null result as clean.

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