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Every workspace gets one long-lived cloud sandbox — the workspace VM — with all your connected repos cloned, dependencies installed, and dev servers running. Each task runs in a disposable fork of that VM, so tasks start from a warm, working state and can’t interfere with each other. This is what makes verification real: the agent doesn’t just compile your code, it runs your app.
The Environment page: workspace VM sizing and environment variables

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Automatic setup

On your first task (or whenever the environment breaks), Twill’s dev environment agent bootstraps the sandbox by reading your repos:
  • Detects package managers from lockfiles (pnpm-lock.yaml, package-lock.json, poetry.lock, …) and frameworks (Next.js, Django, Rails, FastAPI, …)
  • Brings up services from docker-compose.yml and waits for them to be healthy
  • Runs database migrations and seeds
  • Starts dev servers in the background, with logs captured
  • Uses .env.example and your CI config as hints for what the app needs
Fixes made during setup run on the workspace VM itself, so they persist for every future task.
You can trigger this any time: create a task with Dev Env mode — “set up the dev environment”, or “the API server won’t start, fix it”. Changes made in Dev Env mode persist to the workspace VM.

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Environment variables & secrets

Configure variables on the Environment page:
  • Global variables are injected into every task fork.
  • Per-repository variables are written to a .env file inside that repo on the VM.
Values are encrypted at rest (AES-256-GCM). You can also just ask in a task — “I’ve added STRIPE_SECRET_KEY to the environment, wire it up” — and the agent picks it up.

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Live previews

Each task exposes its running app as a live preview: a browser tab streamed from the task’s sandbox, pre-opened on your dev server’s port. Open it from the task header to try the change yourself before the PR lands — no tunnel or proxy configuration needed. Service logs are captured per task under $TWILL_ENTRYPOINT_LOG_DIR and surfaced in the task view (dev-server.log, api.log, entrypoint.log).

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SSH access

Click Open in on the Environment page (or SSH & Preview in a task header) to get a token-scoped SSH command, valid for 60 minutes. Connect from:
  • Your terminal (ssh:// link)
  • VS Code or Cursor via Remote-SSH — full editor access to the sandbox
This works for both the workspace VM and any task fork. It’s the escape hatch: inspect state, fix something by hand, or take over a task midway. The CLI offers the same via twill ssh and twill fork.

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What’s in the sandbox

Repos are cloned to /root/workspace/{owner}/{repo} on an Ubuntu 22.04 base image.
  • Runtimes: Node.js LTS (via nvm), Python 3 - Package managers: pnpm, npm, uv, pip - Containers: Docker Engine with the Compose plugin (docker compose up -d) - CLI tools: git, gh, jq, make, curl, wget, openssl - Cloud CLIs: AWS CLI v2, Google Cloud CLI (authenticated via workspace env vars) - Browser: headless Chromium — Puppeteer and Playwright are auto-detected - Display: Xvfb virtual display, which powers computer-use UI verification
Choose the workspace VM size on the Environment page. Larger sizes and custom snapshots (preinstalled dependencies, GPUs, bigger resources) are available on paid plans — see Pricing. For custom snapshots, contact dan@twill.ai.