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A framework preset is the set of defaults a framework needs to run well: the port it listens on, a health path, how it builds, the environment variables it will not boot without, and the paths worth keeping across deploys. The control plane detects the framework from your repository and fills these in, so a first deploy needs no manual build configuration.

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How it works

When you point the create-app form at a repository, the detector reads the manifest files (package.json, go.mod, pom.xml, requirements.txt, Gemfile, composer.json) and picks a preset. The picker shows the match with a sparkle mark. You can choose a different preset at any time. If the port or health path in the form differs from the preset, the form shows Use preset settings. One click applies the port, health path and build type. Nothing is submitted until you create the app. From the command line:
--framework fills the port, build type and volumes you did not set yourself, and prints a note for any required secret such as SECRET_KEY_BASE. The API is GET /api/v1/frameworks, GET /api/v1/frameworks/{id} and GET /api/v1/frameworks/{id}/dockerfile.

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Presets

Static presets have no port: the built-in web server serves the files directly and no container runs. With the CLI, declare build.type: static in app.yaml and use --file.

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Deploy guides

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Next.js

Set output: 'standalone' in next.config for the smallest runtime image. The preset mounts a volume at /app/.next/cache so ISR pages and optimized images survive a redeploy. NEXT_PUBLIC_* values are inlined at build time, so pass them as build args, not runtime env. levelrail-cli build frameworks nextjs --dockerfile prints a multi-stage Dockerfile with a non-root user.

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Next.js static export

With output: 'export' the detector chooses the static preset. The out directory is served directly.

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React / Vite

The dist directory is served as a static site. Variables prefixed VITE_ are baked in at build time. Single page apps fall back to index.html.

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Astro

Static output is the default and is served directly. For output: 'server' pick Node.js and set the port to 4321.

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Nuxt

The Nitro server listens on 3000. Set NITRO_HOST=0.0.0.0 if the app is unreachable from the proxy.

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SvelteKit

Use adapter-node. ORIGIN must match the public URL or form actions fail the CSRF check.

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Node.js (Express)

Listen on process.env.PORT and bind 0.0.0.0. The detector reads a port from scripts.start when it finds one.

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Go

The preset expects /healthz and a PORT variable. levelrail-cli build frameworks go --dockerfile prints a static build on a distroless nonroot image, a few megabytes in total.

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Spring Boot

Add spring-boot-starter-actuator so /actuator/health exists. The preset allows 120 seconds for readiness because a JVM cold start can be slow, and sets -XX:MaxRAMPercentage=75 so the heap follows the container memory limit. The Dockerfile template builds a layered jar so dependency layers are cached between deploys.

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Django

Set DJANGO_SECRET_KEY as a secret and add your domain to DJANGO_ALLOWED_HOSTS. A 400 response from a fresh deploy almost always means the host is missing. Uploaded files live under /app/media, which the preset persists.

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FastAPI

The default /docs page doubles as a health path. Replace it with a real /health route when you have one.

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Rails

SECRET_KEY_BASE is required. /up is the built-in Rails health route. Active Storage disk files live under /app/storage, which the preset persists.

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Laravel

APP_KEY is required: generate it with php artisan key:generate --show. /up is the Laravel health route. Uploads and logs live under /app/storage, which the preset persists.

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Test fixtures

Each preset has a minimal sample project under test/fixtures/frameworks/<id>. The detector tests run against all of them, so a change that stops one from being recognised fails the build.
Last modified on October 19, 2026