Isag

Isag (/aɪˈzɑɡ/, "Isolated Agent") — sandboxes coding agents in containers with hard limits on what it can read, write, and reach.

Why

Isag gives the agent full freedom inside a container, while keeping your machine safe outside it. You get:

• A filesystem scoped to what you mount. The agent sees only the directories you explicitly add. Your home directory, your SSH keys, the rest of your host — invisible.
• Read-only mounts when you want them. Mount your project :ro to let the agent analyze without editing. Mount datasets :ro. Mount a scratch directory :rw. The kernel rejects writes to a read-only bind mount regardless of file permissions.
• A network firewall. Outbound traffic is locked to a domain allowlist enforced at the kernel level. Anything else fails to connect — the agent can't lift the rule from inside.
• Optional GPU passthrough. Flip one flag in the config to give the container CUDA + the NVIDIA toolkit.
• Disposable container. Try experimental tooling without consequence — pip at runtime, system packages via extra_packages + rebuild. If something breaks, the host is untouched and Isag brings up a clean one.

Requirements

• Linux host with Docker.
• GPU mode needs the NVIDIA Container Toolkit.
• Tested on Linux and WSL2. macOS (Docker Desktop / Rancher Desktop) and native Windows Docker should work but are untested.

Try it

Install:

pip install isag

Run:

isag init
isag run

You're inside the agent CLI now, in a container that can reach github.com, pypi.org, npm, and the vendor's API — and nothing else.

Expose a container service on the host's loopback. E.g., reach the container's SSH or Jupyter from your host (useful for IDEs and browsers):

isag ssh -L 2222:localhost:22 -L 8888:localhost:8888

Expose a host service to the container. E.g., give the container access to the host's adb server, and through it any devices the host can reach (USB, network, or via VPN):

isag ssh -R 5037:localhost:5037

The config file

isag init writes a starter isag.yaml. The lines you'll touch:

project: ~/code/my-project:/workspace/project:rw   # use :ro for analysis-only runs
agent:
  vendor: claude                                   # claude or codex
  cli_flags: null                                  # extra arguments, e.g. ["--model", "my-model"]
  share_vendor_homes: false                        # true also mounts existing other vendor folders read-write
  host_home: ~/agents                              # vendors persist here as host_home/.claude, host_home/.codex; set to ~ to share history + credentials with your host install
container:
  python: 3.14                                     # container system-wide Python
  image: ubuntu24.04                               # or e.g. nvidia/cuda:12.8.1-runtime-ubuntu24.04 if gpu:true
  gpu: false                                       # true for CUDA + NVIDIA toolkit
  host_cache_dir: ~/isag-cache                     # mounting pip, npm, and other caches          
limit_network:
  domains:                                         # everything else is blocked
    - github.com
    - pypi.org
    - registry.npmjs.org
mounts:
  - ~/datasets:/workspace/datasets:ro              # add more mounts; :ro makes them read-only
exclude:                                           # hide paths inside any mount (set to null to disable)
  files:
    - .env
  folders:
    - .git

• agent.cli_flags and agent.share_vendor_homes are required; add both to existing configs. Flags are appended after the YOLO flag; null or [] adds nothing.
• Set limit_network: null to turn the firewall off entirely. Useful on trusted networks; not the default for a reason.
• Excluded paths are host paths; if they fall under project or any mounts entry, the corresponding container path is overlaid with an empty mount.
• Both absolute and relative paths on the host are permitted for all fields. If a field path is relative, it is resolved relative to the project host path. If the project host path is also relative, it is first resolved relative to the YAML file path.
• Command isag run displays the cache directory. Open it to view the files and commands used to run the project.

What it doesn't protect

• Anything you mount writable — the agent has full access there.
• Sibling containers, if you opt into external_networks.
• Anything the agent can do at an allowlisted endpoint with credentials you gave it.

License

Apache-2.0.