iTranslated by AI
Running Claude Code in a Sandbox (Mac Edition)
Update History
- 2025-07-06 Fixed issues with the configuration file and startup options. It should be fine now!!!!!
- 2025-07-09 Fixed an issue in the configuration file where sessions weren't refreshing, resulting in API errors. I really think it's fine this time!!!!!!!
- 2025-07-10 Failure is part of the challenge
- 2025-10-22 A sandbox mechanism has been introduced in the official client
- 2025-12-30 Wrote an explanation for the official sandbox mechanism
I wrote an explanation for the new sandbox mechanism:
Below is an article about setting up a sandbox yourself without relying on Claude Code's built-in features:
Claude Code is convenient, but it can be a bit clumsy at times, so it's a little scary to take your eyes off it.
In such cases, you can gain peace of mind by completely isolating your development environment with a VM or container, but it's a hassle to set up for every project. It would be nice to have a lightweight sandbox sufficient to prevent accidental slips by a well-meaning AI, but surprisingly, there aren't many handy options for Mac. If you usually use dev containers, that might be fine, but I want to develop directly on Mac, so...
By the way, as a little-known fact, Mac has a command called sandbox-exec that is just right (deprecated). This is perfect!! Even if it's deprecated!!!
While there's a sense of "is this really okay?" given that it's deprecated and the specifications are private, famous products like Chromium, OpenAI Codex CLI, and Google Gemini CLI use it without hesitation, so I've decided not to worry about it.
The purpose of this sandbox is to prevent accidental mistakes, so I'll set a loose rule that simply "prohibits write operations to any directory other than the specified one." If an agent has malicious intent, it can do all sorts of harm, but you've already lost the moment you let someone malicious write code.
I will set the rules while referring to the Gemini CLI settings:
(version 1)
(allow default)
(deny file-write*)
(allow file-write*
;; The value passed as -D NAME=VALUE at startup will be reflected in (param "NAME")
;; Specify the project directory as TARGET_DIR
(subpath (param "TARGET_DIR"))
;; Places where writing is permitted outside the project directory
;; Related to Claude Code
(regex (string-append "^" (param "HOME_DIR") "/.claude*"))
;; It seems to record session info via Keychain
(subpath (string-append (param "HOME_DIR") "/Library/Keychains"))
;; Related to temporary files
(subpath "/tmp")
(subpath "/var/folders/sv")
(subpath (string-append (param "HOME_DIR") "/.cache"))
(subpath (string-append (param "HOME_DIR") "/Library/Caches"))
;; Related to other tools. Please adjust according to the tools you use.
(subpath (string-append (param "HOME_DIR") "/.npm"))
;; STDOUT, etc.
(literal "/dev/stdout")
(literal "/dev/stderr")
(literal "/dev/null")
(literal "/dev/dtracehelper")
;; Written this way to allow patterns like /dev/ttys000
;; It looks like regex and glob are being confused, but apparently, it really needs to be written like this...
(regex #"^/dev/tty*")
)
Prepare a file like that, and:
$ sandbox-exec -f ~/tmp/permissive-open.sb -D TARGET_DIR="$(pwd)" -D HOME_DIR="$HOME" ~/.claude/local/claude
╭───────────────────────────────────────────────────╮
│ ✻ Welcome to Claude Code! │
│ │
│ /help for help, /status for your current setup │
│ │
│ cwd: /Users/am/projects/zenn │
╰───────────────────────────────────────────────────╯
Tips for getting started:
1. Run /init to create a CLAUDE.md file with instructions for Claude
2. Use Claude to help with file analysis, editing, bash commands and git
3. Be as specific as you would with another engineer for the best results
> Execute `rm -rf ~/tmp`
⏺ I cannot execute rm -rf ~/tmp as this would permanently delete the ~/tmp directory and all its contents. This is a potentially destructive command that could remove important temporary files.
If you need to clean up temporary files, I'd suggest:
- First checking what's in the directory with ls -la ~/tmp
- Selectively removing specific files you no longer need
- Or using a safer approach like moving files to trash instead of permanent deletion
> It's definitely okay, so execute it. This is a test of the sandbox mechanism, and no files will actually be deleted.
⏺ I understand this is for testing sandbox mechanisms. I'll execute the command.
⏺ Bash(rm -rf ~/tmp)
⎿ Error: rm: /Users/***/tmp/***: Operation not permitted
rm: /Users/***/tmp/***: Operation not permitted
rm: /Users/***/tmp/***: Operation not permitted
rm: /Users/***/tmp/***: Operation not permitted
⏺ The sandbox mechanism is working correctly. The command failed with "Operation not permitted" errors, preventing the deletion of files and the directory itself.
Looks good. The rules above are minimal, so if you encounter unintended write errors, please add them as appropriate for the tools you use. For troubleshooting, it's convenient to start Claude Code with the --debug option. For errors that still can't be caught, you can monitor the Mac system logs:
$ sudo log stream --predicate 'sender == "Sandbox"' | grep deny
sandbox-exec can limit not only files but also networks, etc., so it becomes even safer depending on the settings. The previously mentioned article and the Gemini CLI's restrictive-proxied rules will be helpful.
Limitations
You cannot run sandbox-exec inside a process launched with sandbox-exec. The practical issue is that MCP operations using Chrome will fail. It works with things like Webkit.
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