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mcp-security-scanner

mcp-security-scanner

by badchars
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
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rt_check_scope_creep

Detects over-permissive parameters and excessive tool counts in MCP schemas to mitigate security scope creep.

Instructions

Analyze tool schemas for over-permissive parameter types: arbitrary file paths, unrestricted URLs, shell commands, wildcard globs, any-type schemas. Also flags excessive tool count (>50).

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "rt_check_scope_creep"
  }
}

Input Schema

NameRequiredDescriptionDefault
envNoAdditional environment variables for stdio
urlNoMCP server URL for HTTP/SSE transport (e.g. 'http://localhost:3000/mcp')
argsNoCommand arguments for stdio (e.g. ['run', 'server.js'])
commandNoServer command for stdio transport (e.g. 'node', 'bun', 'npx')
headersNoCustom HTTP headers (e.g. { 'Authorization': 'Bearer token' })
timeout_msNoConnection timeout in milliseconds (default: 30000)

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed6 schema fields changedv1.1.1
    • changedInput schema / properties / args / description
      Previous value: -"Command arguments (e.g. ['run', 'server.js'])"New value: +"Command arguments for stdio (e.g. ['run', 'server.js'])"
    • changedInput schema / properties / command / description
      Previous value: -"Server command to execute (e.g. 'node', 'bun', 'npx')"New value: +"Server command for stdio transport (e.g. 'node', 'bun', 'npx')"
    • changedInput schema / properties / env / description
      Previous value: -"Additional environment variables"New value: +"Additional environment variables for stdio"
    • addedInput schema / properties / headers
      Added value: +{
+  "additionalProperties": {
+    "type": "string"
+  },
+  "description": "Custom HTTP headers (e.g. { 'Authorization': 'Bearer token' })",
+  "type": "object"
+}
    • addedInput schema / properties / url
      Added value: +{
+  "description": "MCP server URL for HTTP/SSE transport (e.g. 'http://localhost:3000/mcp')",
+  "type": "string"
+}
    • removedInput schema / required
      Removed value: -[
-  "command"
-]
  2. First observedv1.0.0

TDQS

B3.2/5.0
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. It only lists what the tool checks (patterns and tool count) but does not describe behavioral traits like whether it is read-only, how it processes input, error potentials, or side effects.

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 two sentences long, front-loading the core purpose and listing specific checks. Every sentence is necessary and there is no redundant or filler content.

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?

Given 6 parameters and no output schema, the description should explain what results look like (e.g., warnings, issues, structure). It does not address the output format or how the analysis is performed, leaving the agent uninformed about the tool's response.

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% with all 6 parameters having descriptions. The tool description adds no additional meaning beyond the schema; it does not mention parameters. Baseline of 3 is appropriate as the schema already defines parameter semantics.

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 analyzes tool schemas for over-permissive parameter types, listing specific patterns (file paths, URLs, shell commands, etc.) and also flags excessive tool count (>50). This specific verb+resource and the enumerated checks differentiate it from sibling runtime check tools.

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, such as other rt_check_* tools or when not to use it. It lacks any context about prerequisites or exclusions.

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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