io.github.daedalus/mcp-cryptography

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rsa_sign

Create an RSA digital signature for a given string using a private key in PEM format. Returns a Base64-encoded signature.

Instructions

Create RSA digital signature.

Args: private_key_pem: RSA private key in PEM format. data: String to sign.

Returns: Base64-encoded signature.

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": {
      "private_key_pem": "<private_key_pem>",
      "data": "<data>"
    },
    "name": "rsa_sign"
  }
}

Input Schema

Name	Required	Description	Default
`data`	Yes
`private_key_pem`	Yes

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.1Jul 30, 2026

TDQS

A3.8/5.0

Behavior3/5

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

No annotations provided. The description states 'Returns: Base64-encoded signature' but does not disclose internal behavior (e.g., whether it hashes data first, key size requirements, or error conditions). Adequate for a simple operation but lacks depth.

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?

The description is very concise, using clear section headers (Args, Returns). Every sentence adds value without redundancy.

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

Completeness4/5

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

For a simple signing tool, the description covers purpose, inputs, and output. With an output schema indicated, the return format is explained. Lacks edge cases or error handling, but is mostly complete.

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 description coverage is 0%, but the description adds meaning to both parameters: 'RSA private key in PEM format' for private_key_pem and 'String to sign' for data. This provides semantic value beyond the schema types.

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 'Create RSA digital signature' with a specific verb and resource. It distinguishes from sibling tools like rsa_verify and rsa_encrypt by explicitly focusing on signing. Parameters and return value are also explained.

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?

No explicit guidance on when to use this tool versus alternatives. Siblings include verification and other cryptographic operations, but no context is given for choosing rsa_sign over them. Only implied usage.

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