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

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered; the description adds genuinely new context: free tier with a per-caller daily quota, and that payment credentials (X-Payment / X-Payment-Tx / Bearer fg_...) belong in MCP request headers, not in parameters. That header-vs-parameter warning is exactly the kind of invocation detail annotations cannot express. It does not describe response shape or quota-exhaustion behavior.

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 core statement is front-loaded and effective, but the content is triplicated across the English summary, the [zh] block, and the [en] block, including a third restatement of the argument list. Everything is relevant, but the bilingual duplication costs density without adding information.

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 its duty by explaining what comes back: a yes/no on known vulns, a count, and a severity distribution. For a three-parameter read-only lookup that is close to sufficient; the remaining gap is the unspecified ecosystem vocabulary, which matters because a bad ecosystem string would silently change results.

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 0%, so the description must carry parameter meaning, and it does not. It merely restates the three parameter names in both Chinese and English, adding only that ecosystem and version are optional — which the schema's required list already shows. No accepted ecosystem identifiers (npm, PyPI, etc.), version syntax, or default behavior is given.

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 states a specific question it answers ('is this open source package vulnerable') and precisely scopes the output: whether known vulns exist, how many, and the severity mix. It also distinguishes itself from the paid full report, so an agent knows this is a free triage probe rather than the full check. It does not name the sibling paid tool explicitly, which keeps it just short of a 5.

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?

There is clear routing guidance: use this free preview to decide whether it is worth spending $0.05 on the full report. That tells the agent both the purpose and the escalation path. It lacks any explicit when-not-to-use statement (e.g., when a version-specific verdict is already required).

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