A template is one YAML file, template.yaml at the root of its repository — see Publishing. This is the worked example the validator's own tests run against — Umami, one app and one database:

version: 1
minCubeship: "0.6.0"
project: umami            # suggested slug; the installer may change it

inputs:                   # what the template cannot know
  - key: domain
    type: domain
    label: Where the dashboard answers
  - key: appSecret
    type: secret
    label: The app's session secret
    generate: 32          # the instance generates it and shows it once

databases:
  - key: db                # template-local; what references name
    name: umami-db         # suggested instance name, renamable at install
    engine: postgres
    version: "18"
    database: umami        # the password is generated, never written here

apps:
  - key: web
    name: web
    image: ghcr.io/umami-software/umami
    tag: postgresql-v2
    port: 3000
    health: /api/heartbeat
    domains:
      - host: ${input.domain}
    attach:
      - database: db      # contributes DATABASE_URL and friends
        prefix: ""
    limits: { cpu: 1, memory: 1Gi }
    scale: 1
    env:
      APP_SECRET: ${input.appSecret}
      DATABASE_TYPE: postgresql

Every key not shown below is optional and takes the default listed. Unknown keys are refused — see schema.unknown-key.

Top level

Key	Default	Meaning
`version`	—	Always `1`. The only value the validator speaks right now.
`minCubeship`	none	A semver range the installing instance must satisfy, e.g. `">=0.6.0"`.
`project`	—	The suggested project slug. The installer may rename it.
`environment`	`production`	The suggested environment inside that project.
`inputs`	`[]`	What the installer is asked. See Inputs.
`databases`	`[]`	The managed databases this template needs.
`stores`	`[]`	The managed object stores this template needs.
`apps`	—	At least one. What actually runs.

Keys and names are two different things

Every input, database, store and app has a key — lowercase or mixed case, letters/digits/dash/underscore, starting with a letter — which never leaves the file. It is what a reference like ${db.db.host} names, and what attach.database or attach.store names, and it is how one part of the template points at another. See References.

A database, store or app also has a name, which defaults to its key and is what appears on the instance. The installer may change any name, and for databases and stores it sometimes has to: their names are unique across the whole instance, so two installs of one template would collide on the first one otherwise.

Databases

Key	Default	Meaning
`key`	—	Required. What `attach` and `${db.<key>.…}` name.
`name`	the key	The suggested instance name.
`engine`	—	Required. One of `postgres`, `mysql`, `mariadb`, `redis`, `mongodb`.
`version`	the newest offered	Pinning it is advised but not required.
`username`	the engine's default	Redis is always `default`; MySQL and MariaDB refuse `root`.
`database`	none	The database name inside the engine. Ignored on engines with none, like Redis.
`expose`	not exposed	`null` (the default) keeps it internal only; `0` asks for a port picked for you; a number asks for that port.
`limits`	none	See Limits.

There is no password field. A database's password is generated by the instance and handed to an app through an attachment — a template that could write one down would be a template that could steal one.

Stores

Key	Default	Meaning
`key`	—	Required. What `attach` names.
`name`	the key	The suggested instance name.
`version`	none	The MinIO version, unvalidated here — the instance decides what a missing one means.
`buckets`	`[]`	The buckets to create inside it.
`limits`	none	See Limits.

A template cannot declare a linked S3 endpoint — that would be somebody's credential. A template that wants one asks for an input of type store instead, and the installer picks a store that already exists on the instance.

Apps

Source

An app is exactly one of an image or a build — never neither, never both:

Key	Default	Meaning
`image`	none	A public image, with no tag in the string — `tag` is its own field.
`tag`	none	The tag for `image`. Refused on a build: a built app is tagged by its deploy, not by you.
`repo`	none	An `http`, `https` or `git` URL, with the branch in `ref`, never after a `#`.
`ref`	the repo's default branch	The branch or tag to build.
`build`	none	`dockerfile` or `railpack`. Required once `repo` is set.
`dockerfile`	`Dockerfile`	Only meaningful with `build: dockerfile`.

Network

Key	Default	Meaning
`port`	none	The port the app listens on. Also the default for a domain that names none.
`health`	off	A path starting with `/`, no `?` or `#`, at most 255 characters. Strongly advised — see `advice.no-health`.
`domains`	`[]`	See below.

Each entry under domains is { host, port }. host must come from exactly one input of type domain — ${input.<key>} and nothing else, never a literal hostname. port defaults to the app's own port, and beneath that to 8080.

Attach

Each entry under attach wires one database or one store into the app's environment — exactly one of database or store per entry, naming its key:

Key	Default	Meaning
`database`	—	A database's key, exclusive with `store`.
`store`	—	A store's key, or the key of an input of type `store`, exclusive with `database`.
`bucket`	—	Required with `store`: which bucket the app gets.
`prefix`	`""`	Upper case, ending in `_`, like `ANALYTICS_`. Distinguishes two attachments that would otherwise write the same variable names.

A database attachment contributes <PREFIX><STEM>_URL, _HOST, _PORT, _USER, _PASSWORD, and _NAME unless the engine has no named databases — STEM is DATABASE for postgres, mysql and mariadb, REDIS for redis, MONGO for mongodb. A store attachment contributes <PREFIX>S3_ENDPOINT, _REGION, _BUCKET, _ACCESS_KEY_ID, _SECRET_ACCESS_KEY, _PATH_STYLE.

Environment

env is a map of names to values, merged into the app on top of whatever attach already wrote — an app's own env wins on a collision, which is how you point at a different target without detaching anything. A value may itself be a reference, like ${input.appSecret} above.

Limits and scaling

Key	Default	Meaning
`limits.cpu`	none	Cores, at least `0.01`.
`limits.memory`	none	A size — `512Mi`, `2Gi`, `1500M` — at least `6Mi`.
`scale`	none	How many copies, at least `1`.
`spread`	`false`	Spread copies across machines rather than pack them onto one.
`autoscale.min`	`1`	The floor, at least `1` and at most `max`.
`autoscale.max`	—	Required with `autoscale`. At most `100`.
`autoscale.cpu`	—	Required with `autoscale`. A target above `0`, where `100` means one whole core.

limits and stores/databases' own limits share the same shape.

The template file