Mosaic Sandbox Python SDK

mosaic-sandbox is the Python SDK and CLI for Mosaic Sandbox, a Firecracker-based runtime for coding agents.

Install (Python 3.9 or newer):

python3 --version   # 3.9 or newer
python3 -m pip install mosaic-sandbox

Authenticate once with the CLI:

mos auth --token msk_live_...
mos whoami

Run the CLI smoke test:

mos doctor
mos run --template node-20 node -v
mos create --template node-20 --ssh
mos ssh <sandbox-id> --print-command

Or run the one-command first-run check:

mos smoke

Python example:

from mosaic_sandbox import Sandbox

sbx = Sandbox.create(
    template="node-20",
    endpoint="https://sandbox.mosaicos.com",
    api_token="msk_live_...",
    enable_ssh=False,
)

try:
    result = sbx.run_command("node -v")
    print(result.stdout)
    print(result.tti_ms)
finally:
    sbx.destroy()

LangChain and LlamaIndex tools

Give an agent a sandbox without writing tools for it. Neither framework is a dependency of this SDK; the one you use is imported when you ask for it.

from langchain.agents import create_react_agent
from mosaic_sandbox.integrations.langchain import mosaic_sandbox_tools

agent = create_react_agent(model, mosaic_sandbox_tools(template="python-3.11"))

from llama_index.core.agent import ReActAgent
from mosaic_sandbox.integrations.llamaindex import mosaic_sandbox_tools

agent = ReActAgent.from_tools(mosaic_sandbox_tools(), llm=llm)

The tools — mosaic_run_command, mosaic_run_python, mosaic_run_javascript, mosaic_read_file, mosaic_write_file, mosaic_list_files and mosaic_start_server — share one sandbox, created on the first call rather than when the agent is built. mosaic_start_server returns a public HTTPS preview URL, so "run the dev server and show me" is a single tool call.

Keyword arguments are Sandbox.create's, so snapshot_id= starts the agent in an environment you built earlier. Hold the SandboxToolset yourself if you want to close() it explicitly; close() destroys the sandbox it created but leaves a sandbox you passed in alone, and the toolset is spent either way — a later tool call raises rather than quietly starting a second machine.

Harbor environment provider

Harbor 0.22 and newer can run its trials in Mosaic Sandbox through the first-party provider. Install the optional dependency on Python 3.12 or newer:

python -m pip install 'mosaic-sandbox[harbor]'

Point Harbor at the provider in the trial environment configuration:

[environment]
import_path = "mosaic_sandbox.integrations.harbor:MosaicEnvironment"

Authenticate first with mos login. The provider builds each Docker image or Dockerfile environment once, keyed by its content hash, and starts one Mosaic snapshot replica builds per requested MOSAIC_HARBOR_REPLICAS (default 1) and starts one Mosaic sandbox per trial. Set that variable to an integer from 1 through 16 to spread named snapshot restores across hosts. The optional MOSAIC_HARBOR_TTL_SECONDS variable controls abandoned-trial cleanup and defaults to 3600. Mosaic currently supports Linux single-VM tasks, including no-network and public-IPv4/hostname allowlists; Docker Compose and Windows tasks are out of scope for this provider. A Firecracker guest can run Docker natively, so DinD-style tasks are a plausible follow-up.

Docs: https://sandbox.mosaicos.com/docs/