Your coding agent writes code faster than you can read it. Cosmonic Desktop runs MCP servers and agent code on your own machine, where each one starts with no access to your files, network, or keys until you grant it.
No account required· Run your first sandbox in minutes
Build with your agent
Bring your own coding agent. With the cosmonic-sandbox skill installed in Claude Code, Codex, Gemini CLI, or whatever you run, your agent's code deploys straight into a Desktop sandbox instead of running raw on your machine.
Prefer to stay in the app? Describe what you want to Desktop's Builder. Either way, your app is compiled locally and runs in a sandbox from the first second.
Tiny footprint
A fresh sandbox per call is cheap, and idle workloads cost nothing, so bounding every tool your agent touches is realistic, not a tax you pay for safety.
Under the hood, each workload is a WebAssembly component running on CNCF wasmCloud, so you can deploy at scale and you're never locked in.
How it works
Every workload starts with zero authority: no filesystem, no network, no environment, no clock. It gets exactly the capabilities you grant and nothing else, so a poisoned tool or an injected instruction has nowhere to go. Open Inspect to see the whole boundary before anything runs.
In the box
Three ways to start
Install Desktop and pick a starting point. Whichever you choose, the code runs deny-by-default and you see its boundary before it starts.
Grab a ready-made, already-sandboxed app or MCP server from the built-in catalog and deploy it in a click. Review what it can reach, then run it.
Say what you want in plain language. Your coding agent builds and deploys in a sandbox.
Build an MCP server and register it with Claude Code, Cursor, and other agents in one step. Your agent gets a new tool in your sandbox.
FAQ
The risk isn't the agent; it's the code and MCP servers it runs. Cosmonic Desktop runs each of them in its own WebAssembly sandbox with deny-all egress: no access to your files, network, or keys until you grant it.
Run the MCP server as a Cosmonic Desktop workload. It starts with no file, network, or credential access; you grant exactly the capabilities it needs, and everything else stays denied.
Cosmonic Desktop runs MCP servers on your own machine (no cloud sandbox required), each isolated with deny-all egress by default. It's free on macOS, Windows, and Linux.
Yes. Cosmonic Desktop is free and runs on macOS, Windows, and Linux. It's currently in public beta.
Download Cosmonic Desktop and run your first sandboxed workload in minutes. Free forever for personal use, local, and yours.
macOS · Windows · Linux
It's an early beta. Expect a few rough edges, and tell us what breaks.