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MCP Shell Server

by diegofornalha
OverviewSchemaRelated ServersScoreDiscussions
Python
Remote

MCP Shell Server

codecov

A secure server for executing shell commands that implements the Model Context Protocol (MCP). This server allows remote execution of authorized shell commands with support for input via stdin.

Features

  • Secure Command Execution : Only authorized commands can be executed

  • Standard Input Support : Passes input to commands via stdin

  • Comprehensive Output : Returns stdout, stderr, exit code and execution time

  • Security with Shell Operators : Validates commands after shell operators (;, &&, ||, |)

  • Timeout Control : Sets maximum execution time for commands

Related MCP server: Shell MCP Server

Configuring the MCP client in your Claude.app

Published version

code ~/Library/Application\ Support/Claude/claude_desktop_config.json
{
  "mcpServers": {
    "shell": {
      "command": "uvx",
      "args": [
        "mcp-shell-server"
      ],
      "env": {
        "ALLOW_COMMANDS": "ls,cat,pwd,grep,wc,touch,find"
      }
    },
  }
}

Local version

Settings

code ~/Library/Application\ Support/Claude/claude_desktop_config.json
{
  "mcpServers": {
    "shell": {
      "command": "uv",
      "args": [
        "--directory",
        ".",
        "run",
        "mcp-shell-server"
      ],
      "env": {
        "ALLOW_COMMANDS": "ls,cat,pwd,grep,wc,touch,find"
      }
    },
  }
}

Installation

pip install mcp-shell-server

Use

Starting the Server

ALLOW_COMMANDS="ls,cat,echo" uvx mcp-shell-server
# Ou usando o alias
ALLOWED_COMMANDS="ls,cat,echo" uvx mcp-shell-server

The ALLOW_COMMANDS environment variable (or its alias ALLOWED_COMMANDS ) specifies which commands can be executed. Commands can be separated by commas with optional spaces around them.

Valid formats for ALLOW_COMMANDS or ALLOWED_COMMANDS:

ALLOW_COMMANDS="ls,cat,echo"          # Formato básico
ALLOWED_COMMANDS="ls ,echo, cat"      # Com espaços (usando alias)
ALLOW_COMMANDS="ls,  cat  , echo"     # Múltiplos espaços

Request Format

# Execução básica de comando
{
    "command": ["ls", "-l", "/tmp"]
}

# Comando com entrada stdin
{
    "command": ["cat"],
    "stdin": "Hello, World!"
}

# Comando com timeout
{
    "command": ["long-running-process"],
    "timeout": 30  # Tempo máximo de execução em segundos
}

# Comando com diretório de trabalho e timeout
{
    "command": ["grep", "-r", "pattern"],
    "directory": "/path/to/search",
    "timeout": 60
}

Response Format

Successful response:

{
    "stdout": "saída do comando",
    "stderr": "",
    "status": 0,
    "execution_time": 0.123
}

Error response:

{
    "error": "Comando não permitido: rm",
    "status": 1,
    "stdout": "",
    "stderr": "Comando não permitido: rm",
    "execution_time": 0
}

Security

The server implements several security measures:

  1. Command Whitelist : Only explicitly allowed commands can be executed

  2. Shell Operator Validation : Commands after shell operators (;, &&, ||, |) are also validated against the whitelist

  3. No Shell Injection : Commands are executed directly without shell interpretation

Development

Setting Up the Development Environment

  1. Clone the repository

git clone https://github.com/yourusername/mcp-shell-server.git
cd mcp-shell-server

  1. Install dependencies including test requirements

pip install -e ".[test]"

Running Tests

pytest

API Reference

Request Arguments

Field

Type

Mandatory

Description

command

string[]

Yes

Command and its arguments as array elements

stdin

string

No

Input to be passed to the command

directory

string

No

Working directory for executing the command

timeout

whole

No

Maximum execution time in seconds

Response Fields

Field

Type

Description

stdout

string

Standard output of the command

stderr

string

Command error output

status

whole

Exit status code

execution_time

float

Time taken to execute (in seconds)

error

string

Error message (present only if failed)

Requirements

  • Python 3.11 or higher

  • mcp>=1.1.0

License

MIT License - See LICENSE file for details

Available Tools

1 tool
shell_executeC

Execute um comando shell Comandos permitidos:

ParametersJSON Schema
NameRequiredDescriptionDefault
commandYesComando e seus argumentos como array
directoryYesDiretório de trabalho onde o comando será executado
stdinNoEntrada a ser passada para o comando via stdin
timeoutNoTempo máximo de execução em segundos

TDQS

C2.4/5.0
Behavior2/5

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

No annotations are provided, so the description carries full burden for behavioral disclosure. It mentions 'Comandos permitidos: ' but doesn't specify which commands are allowed, security implications, or output behavior. This is a significant gap for a shell execution tool, as it lacks critical safety and operational details.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness2/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is extremely brief but inefficiently structured, with 'Comandos permitidos: ' left incomplete. It fails to convey necessary information concisely, as the trailing text suggests missing content rather than purposeful brevity.

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?

For a shell execution tool with no annotations and no output schema, the description is insufficient. It doesn't explain return values, error handling, security restrictions, or allowed commands, leaving critical gaps in understanding how the tool behaves and what results to expect.

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%, with all parameters well-documented in the input schema. The description adds no additional parameter semantics beyond what the schema provides, such as examples or constraints on allowed commands. This meets the baseline for high schema coverage.

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

Purpose3/5

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

The description states 'Execute um comando shell' which translates to 'Execute a shell command', providing a clear verb+resource combination. However, it's incomplete with 'Comandos permitidos: ' trailing off, making it vague about what commands are actually allowed. No sibling tools exist for differentiation, but the incomplete nature reduces clarity.

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, prerequisites, or exclusions. It only states the basic purpose without context about appropriate scenarios or limitations, leaving the agent with no usage direction beyond the obvious.

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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TDQS

C2.7/5.0
Disambiguation5/5

With only one tool, there is no possibility for confusion or overlap between tools. The tool 'shell_execute' has a single, clearly defined purpose of executing shell commands, so disambiguation is perfect.

Naming Consistency5/5

Since there is only one tool, naming consistency is inherently perfect. The tool name 'shell_execute' follows a clear verb_noun pattern, but with no other tools to compare, it sets no pattern to deviate from.

Tool Count2/5

A single tool is too few for a server named 'MCP Shell Server', which implies broader shell-related functionality. While the tool covers basic command execution, the scope feels thin, lacking tools for tasks like listing files, checking processes, or managing environment variables that are typical in shell operations.

Completeness2/5

The tool set is severely incomplete for a shell server. It only provides execution, missing essential operations like file manipulation (e.g., read, write, delete), directory navigation, process management, or system information retrieval. This will likely cause agent failures when trying to perform common shell tasks beyond simple command execution.

Maintenance

ActivityInactive
ResponsivenessSyncing

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