ZEN SecDB

cvss_explain

Read-onlyIdempotent

Calculate the score of any CVSS vector string and explain it in natural language.

What this tool does

Takes a CVSS vector string, not tied to a specific CVE, and returns its version, base score, severity, and a human-readable explanation.

When to use this tool

Use this tool when the user:

provides a CVSS vector and asks what it means
wants to see how the score changes when a metric changes
has adjusted a vector for their own environment

For the official CVSS of a CVE, use vulnerability_score.

Inputs

vector_string: CVSS vector string, e.g. CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

Outputs

cvss_version
cvss_base_score
cvss_base_severity
cvss_vector_string
cvss_explain: human-readable explanation of the vector

LLM usage guidelines

Never calculate CVSS scores by hand: use this tool.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "vector_string": "<vector_string>"
    },
    "name": "cvss_explain"
  }
}

Input Schema

Name	Required	Description	Default
`vector_string`	Yes	CVSS vector string

Output Schema

Name	Required	Description
`cvss_explain`	Yes	Explain CVSS
`cvss_version`	Yes	CVSS version
`cvss_base_score`	Yes	CVSS base score
`cvss_base_severity`	Yes	CVSS base severity
`cvss_vector_string`	Yes	CVSS vector string

Schema Changelog

Changes observed during successful MCP inspections.

AddedNov 3, 2026

TDQS

A4.6/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, and non-destructive, so the safety bar is met structurally; the description adds real context by declaring the inputs are user-supplied vectors rather than CVE lookups, enumerating the returned fields, and instructing the agent never to compute CVSS by hand. It does not cover failure behavior for malformed or unsupported CVSS versions, which keeps it from 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.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The sectioned layout is easy to scan and the core action is front-loaded in the opening sentence. Some redundancy exists between the lead line and the 'What this tool does' section, and the Outputs list duplicates what the output schema already declares, costing a little efficiency.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a one-parameter, read-only calculator with a present output schema and full annotations, the description covers purpose, triggers, alternative routing, input format, and return fields. Nothing an agent needs in order to invoke it correctly is absent.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% for the single required parameter, so the baseline is 3, but the description goes further with a fully worked example vector including the CVSS:3.1 prefix, which conveys the accepted format in a way the terse schema description 'CVSS vector string' does not.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb pair (calculate and explain) and a specific resource (a CVSS vector string), and explicitly scopes it to vectors 'not tied to a specific CVE', which cleanly separates it from the CVE-oriented sibling vulnerability_score.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Three concrete triggers are enumerated (user supplies a vector, wants to see score delta when a metric changes, has tuned a vector for their environment), plus an explicit exclusion routing official CVE scores to vulnerability_score. When-to-use, when-not, and the alternative are all named.

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

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