sbx-kits-contrib

Community-contributed kits for Docker Sandboxes.

Each top-level directory is a kit — a declarative artifact containing a spec.yaml and optional files/ directory that extends sandbox agents with additional capabilities.

Documentation

• Kits overview — what kits are and how to use them
• Kit examples — reference examples for common kit patterns
• Build your own agent kit — step-by-step tutorial using the amp kit in this repo

Contributing a kit or a fix? Read CONTRIBUTING.md first — this repo enforces verified commit signatures, so you'll need GPG or SSH signing set up before your PR can be merged.

Note

Kits are experimental. The kit file format, CLI commands, and experience for creating, loading, and managing kits are subject to change as the feature evolves. Bugs and feature requests for the kits in this repo belong in its issue tracker; general feedback on the kit feature itself goes to docker/sbx-releases.

Using a kit

Kits are passed to sbx run (or sbx create) via --kit. The flag accepts a local path, an OCI registry reference, a ZIP archive, or a git+... URL.

The most common form is a git URL targeting this repo:

$ sbx run --kit "git+https://github.com/docker/sbx-kits-contrib.git#dir=code-server" claude

The fragment after # accepts two parameters, both optional:

Parameter	Purpose	Example
dir	Subdirectory inside the repo containing the kit	#dir=code-server
ref	Git ref to check out — branch, tag, or commit SHA	#ref=v1.0.0

Combine them with &:

# Pin to a tag — the recommended form for production use
$ sbx run --kit "git+https://github.com/docker/sbx-kits-contrib.git#ref=v0.2.0&dir=code-server" claude

# Track a branch (less stable; the kit may change under you)
$ sbx run --kit "git+https://github.com/docker/sbx-kits-contrib.git#ref=main&dir=code-server" claude

# Pin to an exact commit SHA — fully reproducible
$ sbx run --kit "git+https://github.com/docker/sbx-kits-contrib.git#ref=abc1234&dir=code-server" claude

Without ref, sbx clones the default branch shallowly. With a branch or tag, sbx clones at that ref shallowly. With a commit SHA, sbx clones fully and checks out the commit.

You can also use SSH instead of HTTPS for private repos:

$ sbx run --kit "git+ssh://git@github.com/docker/sbx-kits-contrib.git#dir=code-server" claude

For local development, point --kit at a directory:

$ sbx run --kit ./code-server/ claude

Repository Structure

sbx-kits-contrib/
├── spec/          # Kit artifact types, loading, and validation (importable library)
├── tck/           # Technology Compatibility Kit — test suite using testcontainers-go
├── <kit-name>/    # Individual kits (amp, code-server, pi, etc.)
└── .github/       # CI workflows

Adding a New Kit

1. Create a directory at the repo root with your kit name (lowercase, alphanumeric + hyphens):

my-kit/
├── spec.yaml
└── files/
    └── home/          # Files copied to /home/agent/ in the container
        └── config.json

There's no per-kit test file to write — the shared TestKitTCK in tck/kit_test.go reads a KIT env var pointing at the kit directory and runs the full TCK suite against it.

2. Write your spec.yaml:

schemaVersion: "1"
kind: mixin
name: my-kit
displayName: My Kit
description: "Short description of what this kit does"

network:
  allowedDomains:
    - example.com
  deniedDomains:
    - tracker.example.com

environment:
  variables:
    MY_CONFIG: "/home/agent/config.json"

commands:
  install:
    - command: "pip install my-tool"
      user: "1000"
      description: Install my-tool
  startup:
    - command: ["my-tool", "serve"]
      user: "1000"
      background: true
      description: Start my-tool

3. Run the TCK locally — from inside the kit's directory:

cd my-kit
../scripts/test-kit.sh

Or from the repo root, naming the kit:

./scripts/test-kit.sh my-kit

Extra flags are forwarded to go test, so ../scripts/test-kit.sh -v -run … works as expected. If you'd rather invoke go test directly, the equivalent is:

KIT="$PWD/my-kit" go test -v -count=1 -timeout 10m -run TestKitTCK ./tck/...

KIT must be an absolute path because go test runs the binary with its working directory set to the package directory (./tck/).

Windows users: the wrapper is a bash script — run it from Git Bash (ships with Git for Windows) or WSL, not from cmd.exe or PowerShell. If you'd rather skip the wrapper, the direct go test invocation above works in PowerShell too — just substitute $env:KIT = "$PWD\my-kit" for the env-var syntax.

Declare every domain your kit needs

A kit's network.allowedDomains is its complete outbound network contract. The CI e2e job runs with a deny-all default policy, so anything not in your allowedDomains is blocked at request time — and any failed request inside an install hook surfaces as sbx create failing.

The non-obvious trap is package managers refreshing every configured source, not just the one you added:

• apt-get update re-fetches metadata for every file in /etc/apt/sources.list[.d/] — including sources the base template added. If any of those returns non-2xx, apt-get exits non-zero even if the package you want is in a different source. For kits built on shell-docker / *-docker templates that means download.docker.com (Docker's apt repo, pre-added by the template) needs to be in your allowedDomains even if you're only installing something from Ubuntu's main archive.
• Ubuntu hosts amd64 packages on archive.ubuntu.com + security.ubuntu.com and arm64 packages on ports.ubuntu.com. List all three for cross-arch coverage; CI is amd64, your Mac is likely arm64.
• npm install, pip install, cargo, go get, etc. each have their own registry/mirror hosts — declare them too.

The fastest way to find out what your install hooks reach is to run the e2e wrapper. It applies a deny-all global policy on a scoped daemon (--app-name sbx-kits-contrib-tck) for you, then runs TestE2EKit — so you get the network contract and every other e2e assertion from one command:

./scripts/test-kit-e2e.sh my-kit

On failure, dump what the proxy blocked:

APP=sbx-kits-contrib-tck
sbx --app-name $APP ls                            # find the tck-e2e-* sandbox
sbx --app-name $APP policy log tck-e2e-<short-uuid>

Every Blocked requests row is a domain your install or startup hook reached for under deny-all. Add the host (column HOST, e.g. download.docker.com:443) to allowedDomains and re-run until the block list is empty.

If you'd rather hand-build a probe sandbox without invoking the test harness (useful when iterating on install scripts without touching the spec), the manual flow is:

APP=sbx-kits-contrib-tck
sbx --app-name $APP policy init deny-all
sbx --app-name $APP create --name probe-my-kit --kit "$PWD/my-kit" <agent> /tmp/sbx-kit-debug || true
sbx --app-name $APP policy log probe-my-kit
sbx --app-name $APP reset --force                 # wipe the scoped daemon

Same --app-name keeps the state isolated from your main sbx and lets sbx --app-name $APP reset --force clean up without touching your day-to-day setup.

TCK Test Coverage

The TCK validates your kit automatically:

• Validation — spec.yaml parses correctly with required fields
• Network policy — allowed domains and service auth are well-formed
• Credential policy — credential sources are properly defined
• Commands — install/startup commands are well-formed
• Environment variables — declared env vars are set in the container
• Container files — files from files/ are injected at the correct paths
• Security — tmpfs mounts (e.g., /run/secrets) are present

End-to-end (e2e) Tests

The default TCK runs every kit assertion against a fabricated testcontainers-go container — fast, deterministic, no sbx needed. The optional e2e layer goes further: it boots a real sbx sandbox from the kit, then verifies the kit's content actually landed inside the running container. It catches things the default TCK can't — install commands that fail under the non-root agent user, ${WORKDIR} placeholders that resolve differently than expected, agent-kit name mismatches, or memory blocks the engine never writes out.

What the e2e test does

tck/e2e_test.go (build-tag e2e, function TestE2ECreateSandbox) drives one kit per run:

1. Loads the kit at $KIT_UNDER_TEST and picks the agent argument — kit name for kind: agent, claude for kind: mixin.
2. Runs sbx create --kit <kit> --name <unique> <agent> <tmpdir> against a temporary workspace.
3. Verifies, via sbx exec, that the running sandbox contains:
   • every environment.variables entry,
   • every file under files/home and every commands.initFiles (with ${WORKDIR} resolved to /home/agent/workspace, the real sandbox workdir),
   • every declared tmpfs mount (plus the implicit /run/secrets),
   • the rendered memory file — Manifest.AIFilename for agent kits (inlined memory) or kits-memory/<kit-name>.md for mixin kits.
4. Cleans up with sbx rm -f <name>.

Prerequisites

• sbx on PATH. Install the latest release from docker/sbx-releases.
• The scoped daemon must be logged in to Docker Hub once per machine. Interactive form:

  sbx --app-name sbx-kits-contrib-tck login

  Non-interactive (matches CI):

  printf '%s' "$DOCKERHUB_TOKEN" | sbx --app-name sbx-kits-contrib-tck login --username "$DOCKERHUB_USERNAME" --password-stdin

• Linux with /dev/kvm accessible (for the sailor microVM). On Linux runners and most workstations this is already the case; in CI the workflow does sudo chmod 666 /dev/kvm to relax permissions.

Running locally

The test is hidden behind the e2e build tag so kit authors running go test ./... see no behavior change. Opt in via the wrapper — the script handles the --app-name scoping and deny-all policy for you:

# From inside the kit's directory:
cd my-kit
../scripts/test-kit-e2e.sh

# Or from the repo root, naming the kit:
./scripts/test-kit-e2e.sh my-kit

Idempotent and non-interactive. Re-running converges on the same state — set the same default policy, run the test, leave the scoped daemon as it was. Overrides via env: APP_NAME (default sbx-kits-contrib-tck) and POLICY (default deny-all; set POLICY= to skip the policy step). Extra positional flags are forwarded to go test.

If you'd rather drop to go test directly (note: this skips the policy-set step, so you need to apply deny-all yourself or the network contract isn't tested):

KIT_UNDER_TEST="$PWD/my-kit" \
  go test -tags=e2e -v -timeout 25m -count=1 -run TestE2ECreateSandbox ./tck/...

KIT_UNDER_TEST must be an absolute path: go test runs each binary with its working directory set to the package directory (./tck/), so a relative path resolves against ./tck/, not the repo root.

To run every kit locally:

for spec in $(find "$PWD" -mindepth 2 -maxdepth 2 \( -name spec.yaml -o -name spec.yml \)); do
  ./scripts/test-kit-e2e.sh "$(dirname "$spec")"
done

Each subtest (env, files/<path>, tmpfs/<path>, memory) reports independently, so a failure pinpoints which piece of kit content didn't make it into the container.

Running in CI

The test-kit-e2e job in .github/workflows/tck.yml runs alongside the default test-kit job. It downloads the latest sbx release, signs in to Docker Hub using DOCKERHUB_USERNAME / DOCKERHUB_TOKEN repo secrets, then runs the e2e test once per detected kit. The job is skipped on fork PRs because GitHub does not expose secrets to fork-triggered workflows — so for the typical contributor, e2e never runs in CI on their PR, and the reviewer sees a green check that does not cover the e2e assertions.

That makes a local e2e run mandatory before opening a PR from a fork. Run ./scripts/test-kit-e2e.sh <kit> — the script applies the same deny-all baseline CI uses on a scoped daemon (--app-name sbx-kits-contrib-tck), so the network contract gets tested without touching your main sbx state. See Declare every domain your kit needs for the recurring "read the proxy log, add a host, re-run" loop.

Extending a Parent Agent

By default, mixins use the shell template image. To extend a specific agent (e.g., Claude, Gemini), add the extends field:

schemaVersion: "1"
kind: mixin
name: my-claude-extension
extends: claude
# ...

The TCK resolves the parent's template image automatically for well-known agents (shell, claude, codex, copilot, cursor, docker-agent, droid, gemini, kiro, opencode). For other parents, use WithImage:

suite, err := tck.NewSuiteFromDir(".", tck.WithImage("my-custom/template:latest"))

Packages

spec — Kit Artifact Format

Importable library for parsing, validating, and working with kit artifacts:

import "github.com/docker/sbx-kits-contrib/spec"

artifact, err := spec.LoadFromDirectory("./my-kit")

tck — Technology Compatibility Kit

Test framework that validates kit artifacts against real containers:

import "github.com/docker/sbx-kits-contrib/tck"

suite, err := tck.NewSuiteFromDir(".")
suite.RunAll(t)

CI

Pull requests trigger TCK tests automatically:

• Kit changes: only the modified kit is tested
• TCK/spec changes: all kits are tested
• Each kit runs in a separate CI runner on Linux
• The optional test-kit-e2e job exercises every detected kit against a real sbx CLI — see End-to-end (e2e) Tests. Skipped on fork PRs (no Docker Hub secrets).

Prerequisites

• Go 1.23+
• Docker (for container-based TCK tests)