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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds material context the agent cannot get from annotations: strict validation semantics (rejects duplicates and unknown metrics), a plain-language label for every metric, the qualitative severity return, and a pay-per-call model at $0.001 USDC via x402 with an HTTPS fallback endpoint. Payment/auth and error behavior are exactly the kind of detail annotations never carry.

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?

Verb and scope are front-loaded, and each clause (versions, per-version outputs, validation, pricing, alternate endpoint) carries distinct information. It is dense rather than wasteful, though the long parenthetical enumerations make it heavier than it needs to be for a single-parameter tool.

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 still tells the agent what comes back — scores, macrovector, severity breakdown, and plain-word labels — plus the payment model and an alternate transport. Nothing needed to invoke it correctly or interpret the result 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 coverage is 100% and the schema already gives a v4.0 example, so the baseline is 3. The description adds the accepted version list including v3.0 (not shown in the schema example) and confirms the argument is a full vector string rather than individual metrics, which meaningfully narrows interpretation.

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?

Opens with a specific verb+resource ('Score and explain any CVSS vector') and enumerates exactly which CVSS versions and which sub-scores are produced (macrovector, severity breakdown, impact/exploitability, temporal/environmental). An agent can immediately distinguish this from siblings like cve_lookup or epss_score, which look up identifiers rather than score a supplied vector.

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?

The precondition is unambiguous: you must already hold a CVSS vector string in one of four supported versions, and invalid/duplicate/unknown metrics are rejected. It does not explicitly contrast itself with adjacent tools (cve_lookup, epss_score) or say when not to use it, so it falls short of the 5 benchmark for explicit routing.

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