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Parselbox

Runs Python code in a Deno/Pyodide sandbox and exposes MCP, API, shell, filesystem, package, and background-task capabilities.

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Install Parselbox

Pick your client, then add it in one click or paste the config.

STDIOPython
~/Library/Application Support/Claude/claude_desktop_config.json
claude_desktop_config.json
{
  "mcpServers": {
    "parselbox": {
      "command": "uvx",
      "args": [
        "parselbox"
      ]
    }
  }
}

Settings → Developer → Edit Config, merge this into mcpServers, then fully quit and reopen Claude Desktop.

We couldn’t confirm it starts correctly

We ran the install command but it didn't respond within our test window — this can mean a slow first-time install rather than a real problem.

uvx parselbox

No response to initialize.

This is an experimental automated check and can have false negatives — missing environment variables, a slow cold install, etc. It doesn’t necessarily mean something’s wrong. Last checked 8d ago.

Overview

Parselbox MCP server gives agents a Python execution layer that turns MCP servers, APIs, shells, and host functions into Python objects. It runs code in a Deno and Pyodide process with filesystem mounts, package support, network controls, timeouts, and memory limits. The standalone CLI can connect to existing MCP configurations over stdio or HTTP, while the Python API supports embedding the runtime in an agent stack. Reach for it when workflows require multi-step tool composition, data transformation, persistent files, or background execution.

Use cases

  • Compose multiple MCP tools in one Python execution
  • Process API results and save generated files
  • Run parallel background tasks against connected services
  • Expose existing MCP configurations through a sandbox
  • Build small interactive UIs from sandbox output

Key features

  • Python code execution with persistent state
  • MCP, REST, GraphQL, shell, and host-object bridges
  • Disk-backed workspace with host mounts
  • Controlled networking and filesystem permissions
  • Background tasks and progressive tool discovery
  • JavaScript, npm, and WebAssembly interoperability

Security & health

What it can reach and how reliably it runs — from our own checks, not the maintainer’s claims.

ActiveLast checked 3d ago

Recent health check succeeded.

8/8 checks healthy over the last 51d

Supply-chain signal

No high-severity advisories surfaced by our automated scan.

Critical 0High 0Medium 0Low 0

Scanned 13d ago via OSV.dev · parselbox (PyPI)

Adoption & maintenance

Factual signals from GitHub, npm, and our automated checks — not a rating.

GitHub stars3Stargazers on the source repository.
Last commit1mo agoMost recent push to the default branch.
Install checkInconclusiveDidn't respond in our test window — often a slow first install.
Directory activity1 viewsConfig copies, upvotes, and views on AllMCPs.

How Parselbox works

What Parselbox MCP server does

Parselbox MCP server provides an embeddable Python runtime for agent-driven code execution. It can expose configured MCP servers, REST and OpenAPI services, GraphQL endpoints, shell commands, and host-defined functions as Python objects. Agents can then combine those capabilities inside one execution instead of passing intermediate values through separate tool calls.

The runtime includes a disk-backed workspace, package installation, controlled networking, background tasks, and progressive discovery. Files created or changed during an execution can be returned to the caller. The API also supports rendering HTML through MCP Apps and serving a larger application with static files, uploads, live reload, and API routes.

How it works

Parselbox MCP server uses Deno and Pyodide in one process. Deno supplies explicit filesystem and network permissions, while Pyodide provides the Python runtime. The project states that containers and microVMs are not required. Runtime controls include memory caps, execution timeouts, network allowlists, snapshot caching, and crash recovery.

A sandbox can connect to other MCP servers from a supplied configuration. Their tools become callable Python objects, with discovery functions such as help(), search(), inspect(), and preview() available to reveal capabilities as needed. Calls can be made directly or scheduled as background tasks with .task(), progress checks, log tailing, interactive send(), and later awaiting.

Python code can use installed packages and JavaScript interoperability. Imports may install packages automatically when enabled, and npm modules can be loaded through require(). WebAssembly modules can expose Python methods or callable WASI commands. The virtual bash() interface provides shell-style execution within the sandbox.

Setup and configuration

Install Deno first, then install the Python package with pip install parselbox. The command-line MCP server can be added to an existing MCP configuration with uvx parselbox. Its --mcp option accepts a configuration file, and the HTTP transport can be selected with --transport http and a port such as 9000.

The Python API accepts MCP configuration, host context objects, networking settings, runtime-package permissions, package lists, and an output directory. Filesystem access can use read-only or read-write host mounts. Input files are available under /files/, while generated outputs can be persisted to a configured directory.

Tools and capabilities

The Parselbox MCP server supports:

  • Executing Python code with state preserved across calls.
  • Calling MCP, REST, OpenAPI, GraphQL, shell, and host-function integrations as Python objects.
  • Discovering tools progressively with search, help, inspection, and previews.
  • Running parallel or deferred work through background tasks.
  • Reading, writing, and returning files from a disk-backed workspace.
  • Using Python packages, npm modules, JavaScript, and WebAssembly components.
  • Rendering inline HTML or serving a sandbox-hosted application.

Limitations and notes

Parselbox MCP server still depends on Deno for its sandbox runtime, so Deno must be installed for the documented quick-start path. Runtime networking and filesystem access are permission-controlled rather than unrestricted. Host credentials remain outside the sandbox and are supplied through configured bridges or context objects.

The available tools depend on the MCP servers, APIs, shells, packages, mounts, and permissions supplied by the operator. Connecting the server to an MCP configuration should use an absolute path in the documented stdio example.

Read the full README View source on GitHub

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Frequently Asked Questions about Parselbox

Parselbox is an MCP server that connects agents to configured MCP servers, APIs, shells, and host functions through a Python sandbox. Its main tools let agents execute Python, discover available capabilities, compose calls, run background tasks, and read or write workspace files. The runtime uses Deno and Pyodide with controlled permissions.

Install Deno and then install Parselbox with `pip install parselbox`; the standalone MCP command can be run with `uvx parselbox`. Add it to an MCP configuration with the `parselbox` command and pass the relevant file using `--mcp`.

Run `uvx parselbox --mcp mcp.json --transport http --port 9000`. The command starts the MCP server with the selected configuration and listens on the specified port.

Yes. Pass an existing MCP configuration with `--mcp`; Parselbox connects to the configured servers and exposes their tools inside the Python sandbox. It also detects and avoids connecting to itself when used in the documented loopback setup.

Yes. The runtime provides a disk-backed workspace, host mounts, input files under `/files/`, and persisted outputs. It can use Python packages and, when enabled, npm packages through JavaScript interoperability; imports may install packages automatically.

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