composer install and npm install run arbitrary package code with full access to your machine. boxme runs them in a microsandbox microVM, shows you every file change and network contact, and copies the result into your repo only when you approve.

boxme composer install
boxme npm i some-package

Your project is mounted read-only with a throwaway writable layer on top, and tcpdump in the guest records every DNS lookup and outbound TCP SYN. The command runs fully interactively, then a review TUI shows three tabs: Files (expected writes like vendor/ summarized, everything else itemized with diffs), Network (every destination, registry vs unexpected), Outside (writes outside /workspace — reported, never copied back). a applies, q aborts and nothing lands. The base image also blocks dependencies younger than 7 days (composer innobrain/soak-time, npm min-release-age=7).

Needs hardware virtualization: Apple Silicon macOS, or Linux with KVM.

curl -fsSL https://raw.githubusercontent.com/kauffinger/boxme/main/install.sh | sh
boxme setup    # one-time base snapshot, ~10 min; --disk 64 for very large repos

The installer verifies a checksum and installs to ~/.local/bin (BOXME_INSTALL_DIR overrides; append -s -- v0.1.0 to pin a version). Or build from source with cargo install --path . --locked. boxme setup also downloads the pinned microsandbox runtime into ~/.microsandbox — no separate install needed.

Global flags go before the command; everything after composer/npm is passed through verbatim.

boxme composer require foo/bar
boxme npm ci
boxme --strict composer install     # registries only, allowlist ignored
boxme --learn composer install      # re-open the host picker
boxme --keep npm install            # keep the VM after the run
boxme --memory 4096 --cpus 4 composer update
boxme -e NPM_TOKEN=xyz npm install  # env into the guest — visible to package code
boxme -a composer install           # --composer-auth: credentials the guest can't read
boxme composer install ++ composer run-script post-update-cmd
                                    # chain with ++: one sandbox, one combined changeset

A ++ chain runs the commands in order in the same guest and stops at the first failure — so a script hook runs with the install's vendor/ already in place, and everything lands (or is staged, under --json) as one changeset.

Existing vendor/ and node_modules/ stay visible, so incremental commands do incremental work. For a clean install, remove them on the host first or use npm ci.

-e COMPOSER_AUTH hands raw tokens to every postinstall script. -a reads your global composer auth.json and injects each credential as a microsandbox secret: the guest sees only a placeholder, and a host-side TLS proxy splices the real token in — only on a verified connection to that credential's own host. A placeholder aimed at any other host is blocked, so a leaked credential can travel exactly one place: the host it already authenticates.

The host still has to be reachable under the network policy (.boxme/allow); github.com is a built-in registry, so a github-oauth token works right away. Also applies to boxme claude and boxme dev; npm runs ignore it.

Without a terminal there is no TUI, so --json replaces it with a two-step flow — same guarantee, nothing lands without explicit approval:

boxme --json composer install   # run + JSON report on stdout; changeset staged, NOT applied
boxme apply                     # copy the staged changeset into the project
boxme discard                   # or drop it
boxme allow some-host.com       # trust a blocked host without the TUI, then re-run

Step 1 always enforces (registries + .boxme/allow), streams command output to stderr, and prints a report to stdout: changed files with diffs (expected vs unexpected), network contacts (registry/allowed/blocked), outside writes, guest exit code. The changeset is a plain gzipped tar under .boxme/pending/ (self-gitignored, report kept next to it); the report's pending object carries the apply/discard commands so an agent needs no docs.

Exit codes: 0 clean (safe to boxme apply) · 1 boxme failed · 2 the command failed (nothing staged) · 3 findings — blocked hosts, unexpected files, outside writes — listed in findings for a script to branch on.

boxme dev runs your dev stack inside the sandbox and forwards its ports. Dependencies install in the guest (Linux-native binaries — no host/Linux node_modules mismatch), your edits sync one-way host→guest so Vite/HMR sees them live, and nothing the guest writes ever comes back. Ctrl-C tears it down.

boxme dev                              # composer run dev, ports 8000 + 5173
boxme dev npm run dev
boxme dev -p 3000 -p 5173 npm run dev  # custom ports (HOST or HOST:GUEST)

Guest-owned paths aren't synced: node_modules, vendor, .git, storage, bootstrap/cache, public/build, public/hot. Servers that bind only loopback (artisan serve, Vite) are bridged automatically. One VM per folder; several repos at once work, and a busy host port bumps to the next free one. The network policy still applies — without an allowlist, egress is open but recorded.

The database lives in the guest, so run migrations there — attach a second shell from another terminal in the same folder:

boxme attach                       # interactive shell in /workspace
boxme attach php artisan migrate   # one command and exit

boxme claude runs Claude Code inside the sandbox, then copies exactly what it changed into your working tree as plain uncommitted edits — review with git diff, commit or git checkout .. Works on a dirty tree, or a directory that isn't a git repo at all.

boxme claude                        # interactive session (permission mode: auto)
boxme claude 'fix the failing test' # headless one-shot (checks bypassed — the sandbox is the boundary)

If the agent changed a file you'd also edited locally, boxme stops and asks: overwrite, put the work on a boxme/claude-<n> branch, or abort. A headless run branches automatically. The branch is built in a throwaway worktree at HEAD — "HEAD + exactly what the agent did", your working tree untouched.

There is no browser login inside the box (only Anthropic's API hosts are reachable), so authenticate with a token:

claude setup-token   # OAuth on the host, prints a 1-year token
boxme login          # stored in your keychain (Linux: 0600 file), never a dotfile

Resolution order: -e flag → shell CLAUDE_CODE_OAUTH_TOKEN / ANTHROPIC_API_KEY → the saved token; the token is injected into the guest env only. With none, boxme claude fails before booting. Network enforcement is the exfil mitigation: only anthropic.com / claude.com plus the package registries are reachable, so a leaked token can't be sent anywhere else. (A copied subscription login is not reused — its access token expires within hours and the refresh flow doesn't work headless.)

boxme --learn claude '…' observes with open egress and saves contacted hosts to .boxme/claude-allow — kept separate from .boxme/allow so the two surfaces can't inherit each other's reachability. --strict drops the extras.

boxme skills installs two bundled Claude Code skills into ~/.claude/skills:

• fleet-update — "update all repos in ~/Code": runs composer update/npm update via boxme --json in every repo, applies the clean results, reports the rest.
• fleet-fix — security-only, minimal churn: composer fix (innobrain/composer-fix) and npm audit fix, non-breaking fixes only.

Every install runs sandboxed; only clean changesets are applied automatically.

--keep leaves the VM running after a run — useful for autopsy when something failed. boxme claude also keeps the VM automatically if copying the result out fails.

boxme --json --keep composer update   # failed run stays up
boxme ps                              # list boxme's VMs (--json for scripts)
boxme attach [--vm NAME]              # shell into this folder's running VM
boxme exec composer why-not php 8.4   # one command, split streams, exit code propagated
boxme kill boxme-app-3f2a             # stop + remove
boxme kill --all                      # sweep every boxme VM

kill only accepts boxme's own VM names, so it can't remove another tool's sandbox on a typo.

A run either observes or enforces. UDP is always blocked except DNS — that closes the QUIC/raw-UDP exfiltration path the SYN capture can't see.

• No .boxme/allow yet → observe: every TCP connection succeeds and is recorded; the review lets you trust hosts with Space (bare IPs with no resolved name can't be trusted — leave them blocked). If the run only contacted now-allowed hosts, it's copied back as-is; otherwise it re-runs clean under deny-by-default first.
• .boxme/allow exists → enforce: DNS + registries + the allowlist. A newly blocked host shows in the Network tab — mark it with Space, press r, and boxme appends it and re-runs clean under the updated policy. --learn re-opens the full picker; --strict permits registries only.

.boxme/allow is one entry per line — commit it to share with your team:

example.com         # the domain and every subdomain
=api.example.com    # this exact host only
# comments and blanks ignored

There is no mid-run "allow? [y/n]" (the policy is fixed at boot) and no path-level rules (the URL path lives inside TLS — only the hostname is visible).

↑↓/jk select · g/G first/last · h/l/Tab or 1/2/3 switch tabs · Ctrl-d/u half-page · Ctrl-f/b/PgUp/PgDn full page · J/K line scroll · c expand the truncated command · Space trust/mark host · r allow marked + re-run · a approve · q/Ctrl-C abort. Esc is unbound so a reflexive press can't abort a run.

• PHP: php -v from the project dir (mise/asdf/Herd shims resolve per-directory), then composer.json require.php, then 8.4. The image ships 8.3, 8.4 and 8.5.
• Node: node -v from the project dir, then .nvmrc, then engines.node. Majors other than 24 install via n on first use, cached on a named volume.

• The guest gets a git baseline of your tree, including uncommitted changes. Your host repo needn't be a git repo and is never touched by guest git.
• composer/npm download caches are guest-local — no cross-run reuse, but also no shared cache a malicious package could poison. Only the Node-versions volume is shared across projects.
• Approval is all-or-nothing.
• A nonzero exit from the command still shows the review (red banner).
• BOXME_DEBUG_NET=/path/file.txt dumps the raw in-guest tcpdump -r text behind the Network tab.