local-kms-mcp-server

sign_message

Sign a base64-encoded message using a stored private key to generate a digital signature, ensuring message authenticity without external KMS.

Instructions

Sign a base64-encoded message with the stored private key

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": {
      "keyId": "<keyId>",
      "message": "<message>"
    },
    "name": "sign_message"
  }
}

Input Schema

Name	Required	Description
`algo`	No	Override algorithm (uses stored algo if omitted)
`keyId`	Yes	Unique key identifier
`message`	Yes	Base64-encoded message to sign

Output Schema

Name	Required	Description	Default
`signature`	Yes	Base64-encoded signature

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.1.0May 26, 2026

TDQS

B3.2/5.0

Behavior2/5

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

With no annotations provided, the description carries the full burden. It only states the operation without disclosing side effects, return format, or security requirements (e.g., key permissions). Minimal behavioral context.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

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

A single sentence with no unnecessary words. Front-loaded with the verb and resource. Efficient and to the point.

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

Completeness2/5

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

Despite having an output schema and 3 parameters, the description does not mention what the tool returns or the need for the key to be accessible. For a signing operation, more completeness (e.g., algorithm behavior, error conditions) is expected.

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

Parameters3/5

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

Schema description coverage is 100%; the description repeats 'base64-encoded message' from the schema but adds no new meaning. Baseline 3 applies as schema already documents parameters adequately.

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 clearly states the action (sign), the resource (base64-encoded message), and the key used (stored private key). It distinguishes from sibling tools like 'generate_key' (creates keys) and 'delete_key' (removes keys).

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

Usage Guidelines2/5

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

The description provides no guidance on when to use this tool versus alternatives (e.g., check_keypair, rotate_key). It lacks prerequisites (e.g., key must exist) or exclusions.

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

Deploy Server