Modal Provider

Read this when you:

choose provider: modal;
configure the Modal app, sandbox image, working directory, or Python binary;
change internal/providers/modal.

Modal is a delegated-run provider. Crabbox shells out to the local Modal Python client to manage Sandbox lifecycle, upload files, query status, and run commands. Modal owns the sandbox state and process transport; Crabbox owns local config, repo claims, sync manifests and guardrails, slugs, timing summaries, and the normalized list/status output. There is no SSH target.

#When to use

Use Modal when commands should run in Modal Sandboxes and you do not need a Crabbox SSH box. Reach for a provisioned SSH provider (AWS, Hetzner, Azure, GCP, static SSH) or another delegated provider instead when you need crabbox ssh, VNC, code-server, or Actions hydration — none of those surfaces exist on Modal.

#Prerequisites

Install the Modal Python client: pip install modal.
Authenticate Modal locally: python3 -m modal setup, or export

MODAL_TOKEN_ID / MODAL_TOKEN_SECRET. The Python client runs with the current process environment, so any standard Modal auth state is picked up.

#Auth

Crabbox does not take Modal token flags and never passes tokens on the command line. The local Python client reads normal Modal auth state — from python3 -m modal setup or from the environment:

export MODAL_TOKEN_ID=...
export MODAL_TOKEN_SECRET=...

Rotate these values if they were ever pasted into a chat, shell history, issue, or log.

#Commands

crabbox warmup --provider modal --modal-app my-app --modal-image python:3.13-slim
crabbox run --provider modal -- pnpm test
crabbox run --provider modal --id swift-crab --shell 'pnpm install && pnpm test'
crabbox status --provider modal --id swift-crab
crabbox stop --provider modal swift-crab

#Live Smoke

Run the shared smoke only after the Modal Python client is installed and authenticated:

CRABBOX_LIVE=1 CRABBOX_LIVE_PROVIDERS=modal CRABBOX_LIVE_COORDINATOR=0 CRABBOX_LIVE_REPO=/path/to/my-app scripts/live-smoke.sh

The smoke exits before any Modal warmup, status, run, list, or stop call when the configured Python binary cannot import the Modal client. With a working client and auth state, it creates one sandbox, waits for status, runs one no-sync command, lists normalized inventory, and stops the lease.

#Config

provider: modal
target: linux
modal:
  app: my-app
  image: python:3.13-slim
  workdir: /workspace/crabbox/work
  python: python3

Provider flags:

--modal-app
--modal-image
--modal-workdir
--modal-python

Environment overrides:

CRABBOX_MODAL_APP
CRABBOX_MODAL_IMAGE
CRABBOX_MODAL_WORKDIR
CRABBOX_MODAL_PYTHON

Defaults: app crabbox, image python:3.13-slim, workdir /workspace/crabbox, Python binary python3.

#Lifecycle

warmup / run without --id creates a Modal Sandbox in the configured

modal.app from modal.image, with the sandbox timeout and Crabbox ownership tags. Crabbox stores a local claim with a normal cbx_... lease ID and a friendly slug.

The sandbox timeout is derived from --ttl: it defaults to 5 minutes when no

TTL is set and is capped at 24 hours.

By default run archive-syncs the working tree: Git manifest → local

tar -czf → upload to /tmp/crabbox-modal-sync-*.tgz in the sandbox → in-sandbox tar -xzf into modal.workdir.

The user command runs through Sandbox.exec in a bash -lc wrapper that

first cds into modal.workdir, streaming stdout/stderr back through Crabbox.

One-shot sandboxes are terminated after a run that did not pass --keep.

--keep and --keep-on-failure retain the sandbox until crabbox stop.

Note: warmup always keeps the sandbox until an explicit crabbox stop. If you pass --keep=false to warmup, Crabbox prints a warning and still keeps it.

#Capabilities

SSH: no.
Crabbox sync: yes — archive sync through Modal Sandbox upload + exec.
Provider sync: no separate Modal sync step.
Desktop / browser / code: no.
Actions hydration: no.
Coordinator (broker): no — Modal always runs direct from the CLI.
URL bridge / pond: no advertised URL bridge. Modal does not expose a

per-sandbox ingress URL through Crabbox today.

#Gotchas

IDs can be a Crabbox slug, a cbx_... lease ID, or a raw Modal sandbox ID

(when that sandbox carries Crabbox tags).

--class and --type are rejected. The configured Modal image owns the

runtime contents and resources.

modal.workdir must resolve to an absolute, dedicated directory. Broad roots

such as /, /tmp, /home, and /workspace (and other system roots) are rejected before any sync or command runs.

--checksum is rejected because Modal has no SSH/rsync target. Large-sync

guardrails still apply; --force-sync-large is honored for intentional large archive syncs.

Use --sync-only to pre-upload the archive into a kept sandbox before a later

command.

Delegated run/sync options that need an SSH target are rejected:

--script / --script-stdin, --fresh-pr, --full-resync, --env-helper, --capture-stdout / --capture-stderr, --capture-on-fail, --download, --artifact-glob, --require-artifact, --emit-proof, and --stop-after.

Forwarded environment values are written to a temporary shell profile,

uploaded into /tmp, sourced (set -a) for the command, and removed best-effort afterward. They are never placed on the local Python process argv.

Provider backends