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mcp-security-scanner

by badchars

sast_prototype_pollution

Scan source code to detect prototype pollution vulnerabilities including Object.assign with user input, JSON.parse on untrusted data, and bracket notation with user-controlled keys.

Instructions

Detect prototype pollution: Object.assign() with user input, JSON.parse() on untrusted data, bracket notation with user-controlled keys.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
pathYesDirectory path containing source files to analyze
Behavior2/5

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

No annotations are present, so the description must disclose behavioral traits. It only states what it detects but does not mention whether it is read-only, performance impact, or output behavior. Safety and side-effects are not addressed.

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 a single concise sentence that front-loads the key purpose and patterns. No unnecessary words or information.

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

Completeness3/5

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

Given the simple tool (one parameter, no output schema), the description provides the essential detection purpose. However, it does not mention what the tool returns or how results integrate with other tools like report generation, leaving some gaps.

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 coverage is 100% (one parameter 'path' with description). The tool description adds no extra meaning or usage details beyond what the schema already provides, so baseline score of 3 is appropriate.

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 tool detects prototype pollution and lists specific attack patterns (Object.assign, JSON.parse, bracket notation). It differentiates from sibling SAST tools that cover other vulnerabilities like code execution or command injection.

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

Usage Guidelines3/5

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

The description implies usage for detecting prototype pollution but does not explicitly state when to use or when not to use this tool over others. No exclusionary context or alternative guidance is provided.

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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