parallelsandbox-mcp

stdio adapter for the ParallelSandbox MCP server. It exposes the same tools as https://mcp.parallelsandbox.com/mcp (sandbox_*, logs_*), forwarding every call with your API key, and implements sandbox_sync and sandbox_pull locally: an agent can upload its working directory into a box without committing, and write files from the box back to its machine. Get an API key (psbx_…) in the app: https://app.parallelsandbox.com → Account → API keys.

Use

PARALLELSANDBOX_API_KEY=psbx_... npx parallelsandbox-mcp

Claude Code:

claude mcp add parallelsandbox -e PARALLELSANDBOX_API_KEY=psbx_... -- npx -y parallelsandbox-mcp

Any other MCP client: run the command above as a stdio server.

If you never need sandbox_sync or sandbox_pull, you can skip this package and connect directly (over plain HTTP those two tools return an error, because they read and write files on your machine):

claude mcp add --transport http parallelsandbox https://mcp.parallelsandbox.com/mcp --header "Authorization: Bearer psbx_..."

Environment

sandbox_sync

{"id": "<box id>", "localPath": "/abs/path/to/repo", "dest": "repo"} syncs localPath into /work/<dest> on the box. Pass an absolute path: a relative one resolves against this adapter's working directory (where your MCP client started it), which is not necessarily the agent's. In a git working tree it takes the tracked files plus the untracked files .gitignore does not exclude, asks the box which of them differ from what is already in dest, and uploads only those, so syncing after an edit sends just that edit. A file changed inside the box counts as different and gets the local version back. Outside git it uploads the whole directory, excluding node_modules, .git, dist, build, coverage, .venv and similar. Files deleted locally stay in the box.

sandbox_pull

{"id": "<box id>", "path": "<path under /work>", "localPath": "/abs/path/on/your/machine"} downloads a file or a directory from the box. A file is written to localPath. A directory's contents are extracted straight into localPath, the reverse of sandbox_sync: path app/dist with localPath /abs/dist gives /abs/dist/index.html, not /abs/dist/dist/index.html (versions before 0.3.3 added that extra level). Pass "extract": false to keep the tar.gz as one file instead; it holds the directory itself as its top entry. Relative paths resolve the same way as for sandbox_sync. Only the local copy stays: the hand-off copy on ParallelSandbox's side is deleted after about a day.

Which conversation is using a box

Each time the adapter starts it picks a random id and sends it as X-Psbx-Agent on every call. After the first tool call it reports to /v1/agents/<id>/heartbeat once a minute, and when its conversation closes (stdin ends, or SIGTERM, SIGINT or SIGHUP) it reports /v1/agents/<id>/leave. The app uses this to tell a box the AI is still working in from one whose conversation was closed without sandbox_review or sandbox_stop; a conversation killed outright (no leave) counts as gone three minutes after its last heartbeat. Nothing else is sent: no prompt, no transcript.

Timeouts

sandbox_takeover blocks until a person hands the box back, up to 30 minutes; the adapter waits 31 minutes for it and 65 minutes for other calls (a foreground sandbox_exec runs at most 60 minutes).

While a call runs, the server writes a "still running" line on its connection every 20 seconds (every 15 for sandbox_takeover). The adapter forwards those as MCP progress notifications when the client asked for progress, so a client that cancels calls after a stretch of silence (Claude Code does after 30 minutes) keeps waiting for a long build. If the connection ends without the result, or carries nothing for PSBX_ADAPTER_SILENCE_MS, the adapter returns an error right away instead of waiting out the timeout. Read-only tools (sandbox_status, sandbox_list, sandbox_get, the logs_* tools and the like) are retried once first. For anything else the error says the call may have run or even finished on the box: check sandbox_status (its steps[] lists what was run) before running it again.

Source and issues

Source: https://github.com/parallel-sandbox/parallelsandbox-mcp. Report bugs there as issues, or from inside a session with the sandbox_feedback tool. MIT licensed.