landstrip

landstrip runs commands in an OS-level sandbox using Landlock LSM on Linux, Seatbelt on macOS, and AppContainer or restricted local users on Windows. It accepts the Anthropic Sandbox Runtime policy subset in JSON or YAML.

Installation

npm

npm install --save-dev @landstrip/landstrip

npx landstrip -p policy.json cargo test

The npm package installs a small Node.js wrapper and a platform-specific native binary package.

Agent extensions

The bundled extensions integrate Landstrip with Pi and OpenCode. The Pi extension sandboxes Bash execution, provides OpenCode-compatible primary-agent selection, and runs subagents as full Pi RPC processes. Subagents normally run inside an outer Landstrip sandbox; explicitly disabling sandboxing emits a warning and uses a process-only fallback:

pi install npm:pi-landstrip
opencode plugin install opencode-landstrip

See pi-landstrip and opencode-landstrip for configuration details.

Platforms

Area	macOS	Linux	Windows
Policy	path-based rules	file-based rules	per-run ACL grants
Timing	dynamic path subset	static file-based ruleset	per-run grants with cleanup
TCP	proxy or loopback	proxy or loopback	capabilities or account-scoped WFP
Unix sockets	allowlist	seccomp-brokered allowlist	allow all or deny all

Linux

Landlock carves the denied subtrees out of the allowed roots, and then grants PATH_BENEATH rules only for the surviving fragments. The denied path is never added to the ruleset, and the kernel enforces the path directly.

Seccomp is applied when a policy needs more than Landlock can express statically, such as filesystem mutator filtering or denial reporting. The broker intercepts openat and openat2 through seccomp user notifications, resolves the real path, and validates it.

Landlock and seccomp cover mostly disjoint filesystem operations: Landlock handles kernel-enforced path access, while seccomp mediates unsupported mutators and reports broker decisions.

Windows

Landstrip has two Windows backends. AppContainer is the default and needs no installation. The restricted-user backend is an explicit, preinstalled alternative for programs such as Git Bash/MSYS that cannot initialize inside AppContainer. Select the backend with the trusted command-line option --windows-backend; a project policy cannot select it.

Both backends use explicit read allowlists. Ancestors receive traversal-only, non-inheriting access; unrelated siblings are not exposed.

AppContainer

Landstrip creates a per-run profile, grants its SID access to the lowered read and write roots, and removes those grants after the sandboxed process tree exits.

windows.appContainerMode selects "lpac" (the default) or "standard". LPAC provides the stricter boundary. Standard AppContainer can also access resources already granted to ALL APPLICATION PACKAGES, so selecting it is an explicit security downgrade. Landstrip never retries an LPAC launch in standard mode.

Landstrip assigns the sandboxed process to a Job Object with KILL_ON_JOB_CLOSE, so child processes are kept in the sandbox process tree and terminated when the launcher exits. When a restrictive host Job Object prevents safe breakaway, Landstrip fails with HOST_JOB_INCOMPATIBLE; it never launches without its own job.

allowNetwork grants the internet and private-network AppContainer capabilities, while the default container holds none. windows.allowLoopback is a separate, explicit opt-in that temporarily exempts only the per-run AppContainer SID. The exemption permits every local loopback service, not a single proxy port. Existing system exemptions are preserved and the per-run exemption is removed at exit.

AppContainer capabilities are coarse. Fine-grained direct TCP policies by host or port require elevated Windows Filtering Platform rules keyed by the AppContainer SID, which is unsuitable for an unprivileged agent sandbox runtime.

Restricted user

Install the restricted-user backend once from the intended host account. Setup requests elevation through UAC, provisions dedicated local accounts, installs account-scoped persistent WFP rules, and copies a protected broker executable:

landstrip windows setup
landstrip windows status
landstrip --windows-backend restricted-user -p policy.json cargo test
landstrip windows uninstall

The default pool has eight restricted-network accounts and two unrestricted-network accounts. Use landstrip windows setup --help to configure pool sizes and the loopback proxy port range. Setup replaces an existing installation; uninstall revokes recorded ACL grants, removes WFP policy and accounts, and deletes the installed runner.

Each run exclusively leases an account, journals its filesystem grants before applying them, launches the command through a restricted token and Job Object, then revokes the grants. A later lease or uninstall recovers stale journaled grants after a crash. Account credentials are random, stored with Windows DPAPI, and never placed in policy files.

Restricted-network accounts are blocked by WFP except for loopback connections to the proxy port range chosen during setup. Proxy ports in a policy must fall in that range. network.allowLocalBinding and windows.allowLoopback are unsupported by this backend. network.allowNetwork: true instead leases an unrestricted-network account and therefore requires at least one such account in the installed pool.

The restricted token enforces the per-run account-SID grants while retaining the standard ALL APPLICATION PACKAGES read/execute baseline for Windows and Program Files. As with standard AppContainer, resources exposed to that SID remain visible.

Policy format

JSON is the default policy format. Use --format yaml for YAML policy files or YAML read from standard input.

landstrip --format yaml -p policy.yaml cargo test

YAML path fields can use normal lists or one statement per line:

filesystem:
  allowWrite: |
    .
    ~/.cargo
  denyRead: |
    ~/.ssh
  allowRead: |
    ~/.ssh/config
network:
  allowNetwork: true

Filesystem policy

Write access is denied by default. allowWrite paths grant write access and denyWrite paths subtract from them, with the most specific rule winning when allow and deny rules overlap. Read access is unrestricted by default; setting denyRead lowers it to an allowlist, and allowRead adds paths back.

Write-denial semantics

Concrete (non-glob) denyWrite paths are canonicalized and enforced eagerly on all platforms.

Glob denyWrite patterns (**/.env, **/*.pem, and so on) behave differently by platform:

• Linux: Globs are evaluated dynamically by the seccomp broker at each write attempt. Files created after sandbox startup that match a denyWrite glob are blocked. Globs are not walked at startup, avoiding latency on large trees.
• macOS: Globs are snapshot-expanded when the Seatbelt profile is compiled. Files created after sandbox_init are not protected by glob denies; use concrete paths for them. A warning is logged when glob deny patterns are used.
• Windows: Glob denyWrite entries are not enforced by the AppContainer backend.

Network policy

Sandbox mode denies direct network access by default. Proxy ports, loopback TCP binding and connections, and Unix sockets can be allowed with the Anthropic Sandbox Runtime network fields. allowLocalBinding permits both binding to and connecting to loopback TCP addresses, including listeners started outside the sandbox. Linux denies non-loopback connections. On macOS, Seatbelt's required localhost matcher can also include addresses assigned to other local interfaces, but public remote addresses remain denied.

For a filesystem-only sandbox with unrestricted direct network access, set:

{
  "network": {
    "allowNetwork": true
  }
}

allowNetwork disables Landstrip network enforcement while leaving filesystem policy enforcement in place. On Windows, AppContainer receives its network capabilities while the restricted-user backend leases an unrestricted-network account. With allowNetwork: false, AppContainer denies network unless windows.allowLoopback enables the all-loopback exemption described above; the restricted-user backend permits only the installed loopback proxy port range.

A Windows runtime that requires standard AppContainer and loopback can opt in with the following policy:

{
  "windows": {
    "appContainerMode": "standard",
    "allowLoopback": true
  }
}

Core Landstrip defaults to LPAC with loopback disabled.

Traps

Every Landstrip event, whether a sandbox denial or a failure that prevents the tool from running, is reported as one JSON object per line, with a fixed kind discriminant and stable code. Consumers route on kind for the record shape and code for the event. Failures and completed denials go to standard error by default. On Linux, pending query traps go only to --trap-fd FD, which must name an already-open descriptor.

landstrip --trap-fd 3 -p policy.json cargo test 3>landstrip-traps.txt

The trap kinds are:

• filesystem (code FILESYSTEM_DENIED): operation is read or write, path is the resolved path, requested_path is the tool's original path when available, and syscall, errno, flags, reason, suggested_grant, and process carry routing context.
• network (code NETWORK_DENIED): operation is connect or bind and target is address:port, with syscall, errno, and process context.
• launch (code LAUNCH_FAILED): the sandbox was installed but the tool did not start. program is the tool, errno its symbolic errno where the platform has one, and message the system's text.
• usage (code USAGE_ERROR): the command line was rejected. Exits with status 2, and reaches standard error only — the trap descriptor is part of the arguments that failed to parse.
• internal: everything that fails before the tool runs. code names the stage: POLICY_PARSE_FAILED, POLICY_IO_FAILED, SANDBOX_SETUP_FAILED, SUPERVISE_FAILED, PLATFORM_UNSUPPORTED, INTEGER_TOO_LARGE, a POLICY_* validation rejection (POLICY_UNRESTRICTED_READ, POLICY_TCP_BIND_UNSUPPORTED, POLICY_UNIX_SOCKET_UNSUPPORTED, POLICY_UNIX_SOCKET_PATH, POLICY_DENY_WRITE_SYMLINK_ANCESTOR, POLICY_INVALID_PORT, POLICY_EMPTY_PATH, POLICY_HOME_UNAVAILABLE, POLICY_TRAVERSAL_DEPTH), or INTERNAL_ERROR for a failure the code space does not name.

A code names the stage that failed, not the operating system that reported it: the same LAUNCH_FAILED or SANDBOX_SETUP_FAILED is raised by every backend that has that stage. The platform detail rides along in the record instead.

mechanism records the kernel layer an event is attributed to: landlock, seccomp, seatbelt, appcontainer, or windowsuser. Per-denial traps are always seccomp, the only layer with a per-denial callback; Landlock enforces in-kernel without one. SANDBOX_SETUP_FAILED carries the mechanism that could not be installed.

reason is a platform-independent classification of a filesystem decision, derived from the policy and the requested path:

• allow_miss: the path matched no allow root and was denied by default.
• deny_match: the path matched an explicit deny root that overrides an allow.

{
  "kind": "filesystem",
  "code": "FILESYSTEM_DENIED",
  "state": "info",
  "query_id": "0",
  "operation": "write",
  "path": "/repo/out",
  "requested_path": "out",
  "syscall": "openat",
  "errno": "EACCES",
  "flags": ["O_WRONLY", "O_CREAT", "O_TRUNC"],
  "reason": "allow_miss",
  "suggested_grant": { "allowWrite": "/repo/out" },
  "mechanism": "seccomp",
  "process": { "pid": 1234, "exe": "/usr/bin/sh", "cwd": "/repo" }
}
{
  "kind": "network",
  "code": "NETWORK_DENIED",
  "state": "info",
  "query_id": "0",
  "operation": "connect",
  "target": "127.0.0.1:9999",
  "syscall": "connect",
  "errno": "EACCES",
  "mechanism": "seccomp",
  "process": { "pid": 1234, "exe": "/usr/bin/nc", "cwd": "/repo" }
}
{
  "kind": "launch",
  "code": "LAUNCH_FAILED",
  "program": "/usr/bin/cargo",
  "errno": "ENOENT",
  "message": "No such file or directory (os error 2)"
}
{
  "kind": "internal",
  "code": "SANDBOX_SETUP_FAILED",
  "mechanism": "landlock",
  "message": "not enforced by the kernel (Linux 5.13+ with CONFIG_SECURITY_LANDLOCK required, and not disabled via the lsm= boot parameter)"
}

Denial traps are informational; the configured policy always applies. Landstrip is otherwise quiet on success: standard error belongs to Landstrip and standard output to the sandboxed tool. Failure traps include a human-readable log line; machines should read the JSON. Usage errors exit with status 2, other Landstrip failures with 1, and the tool's own status is otherwise passed through.

Writing to --trap-fd is best-effort: it needs an already-open descriptor (3 or greater; 0-2 are reserved), and if the write fails the trap is dropped while the policy stays in effect. On Linux, a broker launch failure also reaches --trap-fd while the descriptor remains open.

Development

Commit messages

• Use <subsystem>: <message> as the subject.
• Add a body for non-trivial changes.
• Follow kernel-style commit message conventions.
• Include a Signed-off-by: trailer.

Documenting errors

The following snippet demonstrates the recommended pattern for documenting the return values on error:

/// # Errors
///
/// Returns [`Variant`] when ...

Licensing

The JavaScript npm wrapper is licensed under Apache-2.0. The Rust source and native binaries are licensed under LGPL-2.1-or-later. Corresponding source for each published native binary is available from the GitHub repository tag that matches the package version.