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mcp-shield

mcp-shield

by muhannad-hash
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Remote

check_prompt_injection

Scan text for prompt injection attacks, hidden instructions, and jailbreak patterns to identify security vulnerabilities in MCP server content.

Instructions

Scan text (tool descriptions, tool responses, MCP server manifest content) for prompt injection attacks, hidden instructions, zero-width characters, jailbreak patterns, and instruction overrides.

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": {
      "text": "<text>"
    },
    "name": "check_prompt_injection"
  }
}

Input Schema

NameRequiredDescriptionDefault
textYesThe text to scan (tool description, response content, etc.)
labelNoA label for the scan target (e.g. 'tool: get_weather description')

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.0.0

TDQS

A3.5/5.0
Behavior2/5

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It describes what the tool does (scanning for specific threats) but lacks details on behavioral traits such as performance characteristics (e.g., speed, accuracy), error handling, or output format. While it mentions what is scanned, it does not disclose how results are returned or any limitations, leaving gaps in transparency.

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, dense sentence that efficiently conveys the tool's purpose, target resources, and scanning criteria without unnecessary words. It is front-loaded with the core action ('Scan text') and avoids redundancy, making every part of the sentence contribute directly to understanding the tool's function.

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 complexity of a security scanning tool with no annotations and no output schema, the description is moderately complete. It covers what the tool does and what it scans for, but lacks details on output (e.g., what results look like) and behavioral aspects like error handling or limitations. This is adequate for basic understanding but has clear gaps for effective agent use.

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%, so the schema already documents both parameters ('text' and 'label') with descriptions. The description adds no additional meaning or context beyond what the schema provides, such as examples or constraints on parameter values. This meets the baseline for high schema coverage but does not enhance parameter understanding.

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 specific action ('Scan text') and the purpose ('for prompt injection attacks, hidden instructions, zero-width characters, jailbreak patterns, and instruction overrides'), with explicit mention of the target resources ('tool descriptions, tool responses, MCP server manifest content'). It distinguishes itself from siblings like audit_supply_chain or scan_directory by focusing on text-based security scanning rather than supply chain or file system analysis.

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 by listing target resources ('tool descriptions, tool responses, MCP server manifest content'), suggesting it should be used for scanning such content. However, it does not explicitly state when to use this tool versus alternatives like scan_package or provide exclusions (e.g., when not to use it for non-text data). The guidance is present but not comprehensive.

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

Deploy Server

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