How does this skill protect my agent from malicious MCP servers?

This skill audits Model Context Protocol (MCP) server definitions to detect prompt injections, risky parameters (like shell command access), and insecure input schemas before you connect them to your agent. It acts as a security gatekeeper to prevent third-party tools from compromising your local environment.

Does the MCP server need to be running or 'live' for the security check to work?

No, this skill performs static analysis on tool metadata and schemas, meaning it never needs to execute the server's code to find vulnerabilities. This allows you to safely inspect potentially dangerous servers in an isolated, execution-free environment.

What are the technical requirements for running the mcp-server-security-check?

This skill requires Python 3.10+ and the `mcp-toolcheck` utility. It is compatible with any AI agent or platform that supports MCP integration, such as Claude Desktop, provided the agent can access the local filesystem to read server definitions.

Does the audit provide actionable advice on how to fix the security issues it finds?

Yes, the skill maps every finding to specific Rule IDs (MCP001-MCP010), providing clear remediation steps and plain-language explanations of why a specific parameter or description was flagged.

Can this skill detect every possible security threat in an MCP server?

While highly effective at catching known patterns like SQL injection vectors and hidden instructions, it cannot detect runtime behaviors or source code vulnerabilities. It is designed to audit what the tool *claims* to do in its metadata, not its internal logic.

Works with the AI Agents you already use

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MCP Server Security Check

Audit MCP servers for prompt injection, risky parameters, and security vulnerabilities using mcp-toolcheck.

Free

Security scanned

MCP Server Security Check

Example session with this skill installed

I'm building a file-manager MCP server. Can you check if this tools.json is safe to use? I've attached the tool definitions for 'read_file' and 'execute_script'.

Read your context and instructions
Compiled the mcp server security

I have scanned 2 tools from your tools.json file using mcp-toolcheck v0.1.0. The audit found 1 high-risk issue and 1 medium-risk issue.

MCP security check: file-manager

Scanned 2 tools with mcp-toolcheck v0.1.0: 1 high, 1 medium, 0 low.

Fix before connecting (HIGH)

execute_script (MCP003): The tool accepts a command string property which allows for arbitrary shell execution. ->

Fix: Replace free-form strings with an enum of allowed scripts or use a restricted configuration file instead of raw command inputs.

Worth reviewing (MEDIUM)

read_file (MCP004): The path parameter allows for absolute file paths which could lead to directory traversal. ->

Fix: Implement path validation in the server to ensure the path is restricted to a specific workspace directory and does not contain .. segments.

What this scan does not tell you

These results are based on heuristics and do not represent a full source code audit. The scan only checks the declared tool metadata, not the actual logic inside your server. I recommend re-scanning if you change the tool definitions.

Next steps

Update the execute_script schema to use an enum for the script_name property.
Add a base_directory constraint to the read_file tool implementation.
Re-run the scan once the schema changes are applied to confirm the high-risk finding is resolved.

Connects securely to your tools. The creator never sees your data.

About this skill

Connecting an untrusted Model Context Protocol (MCP) server to your agent exposes your system to prompt injection and unauthorized file or network access. This skill audits MCP tool definitions to identify risky parameters and hidden instructions before you connect them.

What it does

Scans tool definitions by inspecting names, descriptions, and input schemas for common vulnerabilities.
Detects prompt injection to find hidden instructions in tool descriptions designed to steer the model.
Identifies risky parameters like raw shell commands, file paths, URLs, and SQL injection vectors.
Flags credential requests where a tool inappropriately asks for API keys or secrets in plain text.
Provides remediation by mapping every finding to a specific fix based on established security rules.

How it works

Environment check verifying mcp-toolcheck is installed or requesting permission to install the pinned version via uv or pip.
Definition ingestion where you provide the server's tool list as a JSON file or command.
Automated scanning using the mcp-toolcheck scan command with the --tools-file flag for safe, execution-free auditing.
Result interpretation mapping rule IDs (MCP001-MCP010) to plain-language risk assessments and fixes.

Frameworks & tools

This skill uses the open-source mcp-toolcheck command-line utility. It requires Python 3.10 or newer and can be run via uv or pip.

Why this beats prompting it yourself

Standard LLMs often miss subtle prompt injections hidden in technical schemas or fail to recognize the security implications of specific JSON-schema patterns. This tool uses a specialized heuristic engine and a formal ruleset to ensure consistent detection of known MCP attack vectors.

Use cases

Vetting third-party servers before adding them to your agent's configuration.
Hardening your own MCP server by identifying risky parameter designs during development.
Compliance auditing to ensure internal tools meet security standards for LLM interaction.

Known limitations

This skill uses heuristics that may produce false positives or negatives. It only inspects declared metadata, not the server's source code or runtime behavior. It cannot detect manipulation worded without known trigger phrases.

Uses the open-source mcp-toolcheck scanner (MIT, no API keys, no telemetry) and explains each finding.

Source: https://github.com/cessadev/mcp-toolcheck

How to use

Skills on Agensi run inside your AI agent. Copy the prompt, paste it into your agent, and it connects to Agensi and installs this skill for you. If a payment is needed, your agent shows it to you first.

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uv (Python tool runner)

Python

Listed3 days ago

MCP Server Security Check