What
The sandbox is a protective boundary that limits what commands Claude Code runs can touch. A deny entry is a rule that blocks access to a path. When sandboxing is on and some deny entries point at a path on another computer (a remote host), the sandbox leaves them out. Claude Code now tells you about this in two places:
- At startup, as a warning printed to stderr (the terminal's error output)
- In
claude doctor, which lists the affected entries
The warning begins "Sandbox deny paths on another computer are not enforced, so sandboxed commands are not blocked from them:". It also says the rules still apply to Claude Code's file tools, the built-in tools it uses to read and edit files.
Why
If you wrote deny rules for paths on another computer, those rules do not stop sandboxed commands from reaching them. You now hear about it instead of assuming you are protected.
claude doctor
Error reference modified, high confidence
This warning in `claude doctor` and `/status` lists mask files: 0-byte read-only placeholder files at paths the [sandbox](/docs/en/sandboxing.md) denies writes to. It appears on Linux and WSL2 when sandboxing is enabled with filesystem iso…see the edit
claude doctor
Configure permissions modified, high confidence
To match a parameter on an MCP tool, pass a deny rule with [`--disallowedTools`](https://code.claude.com/docs/en/cli-reference#cli-flags). When Claude Code loads a settings file, it skips any `mcp__` rule that has parentheses. Claude Code …see the edit
claude doctor
Configure the sandboxed Bash tool modified, high confidence
* **TLS termination**: the proxy substitutes the real value inside request contents, so it has to see them. Set [`network.tlsTerminate`](https://code.claude.com/docs/en/settings-reference#sandbox-network-tlsterminate) so the proxy terminat…see the edit
claude doctor
Troubleshooting modified, high confidence
| Session footer shows `Auto-update failed · Run claude doctor` in red | [Troubleshoot installation and login](https://code.claude.com/docs/en/troubleshoot-install.md#auto-update-failed) |see the edit
claude doctor
Configure the sandboxed Bash tool modified, medium confidence
Run `claude doctor` in your terminal to list the leftover placeholder files. The [`Sandbox mask files left behind at write-deny paths`](/docs/en/errors#stale-sandbox-mask-files-left-by-a-killed-session) warning names some of them and count…see the edit
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agrees
claude doctor on Error reference