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pfelilpe

Damn Vulnerable MCP Server Demo

by pfelilpe

addition

Adds two numbers together to calculate their sum, demonstrating basic arithmetic operations within an educational security testing environment.

Instructions

Sum tool

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
aYes

Implementation Reference

  • server.py:9-9 (registration)
    Registration of the 'addition' tool using the @mcp.tool() decorator on the addition function.
    @mcp.tool()
  • server.py:10-12 (handler)
    The handler function for the 'addition' tool, which takes a single argument 'a' (a string expression) and evaluates it using Python's built-in eval() function to compute the result.
    def addition(a):
        """Sum tool"""
        return eval(a) 
Behavior1/5

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

No annotations are provided, so the description must carry the full burden of behavioral disclosure. 'Sum tool' offers no information on traits like safety, permissions, rate limits, or output behavior. It does not describe what the tool does beyond its name, failing to compensate for the lack of structured data.

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 description is extremely concise with 'Sum tool', which is front-loaded and wastes no words. However, this brevity leads to under-specification, as it lacks necessary details, but it is structurally efficient for its minimal content.

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

Completeness1/5

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

Given the tool's complexity (simple but undefined), lack of annotations, no output schema, and 0% schema coverage, the description is completely inadequate. It fails to explain the tool's purpose, behavior, parameters, or output, making it insufficient for effective agent use.

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

Parameters1/5

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

The input schema has 1 parameter with 0% description coverage, and the description 'Sum tool' adds no meaning about the parameter 'a'. It does not explain what 'a' represents (e.g., a number, list, or string), its format, or how it relates to the summation, leaving the parameter undocumented.

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

Purpose2/5

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

The description 'Sum tool' is a tautology that restates the tool name 'addition' without specifying the verb or resource clearly. It vaguely implies mathematical addition but lacks detail on what is being summed (e.g., numbers, strings) or how it operates, making it unclear and minimally informative beyond the name.

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

Usage Guidelines1/5

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

No guidance is provided on when to use this tool, such as context, prerequisites, or alternatives. With no sibling tools, this is less critical, but the description fails to offer any usage instructions, leaving the agent without direction on its application.

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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