YAML Compatibility

A Launchfile is standard YAML 1.2. All YAML features work, and no custom tags are used. See DESIGN.md D-22 for why YAML was chosen.

Arrays don't need extra indentation

The - can sit at the same column as the key. Both forms are valid:

# Indented (common style)
requires:
  - postgres
  - redis

# Flush (equally valid, more compact)
requires:
- postgres
- redis

# Inline (shortest)
requires: [postgres, redis]

Anchors, aliases, and merge keys

Use &name to define a reusable block, *name to reference it, and <<: to merge it into a map:

x-shared: &shared
  runtime: node
  build: .
  health: /health
  env:
    LOG_LEVEL: "info"

components:
  api:
    <<: *shared
    commands:
      start: "node api.js"
    provides:
      - protocol: http
        port: 3000

  worker:
    <<: *shared
    commands:
      start: "node worker.js"
    env:
      LOG_LEVEL: "debug"  # overrides the shared value

The x- prefix is a convention for extension fields that parsers ignore. Merged values can be overridden by declaring the same key after the merge.

Copy semantics: YAML aliases (*name) are resolved to deep copies by the parser — they are not live references. If an anchored block contains a generator: secret definition, each alias produces a separate generated value. For values that must be shared across components, use the $secrets.<name> expression system instead of YAML anchors.

Block scalars for multi-line text

Use | (literal) to preserve newlines, or > (folded) to join lines:

commands:
  release: |
    npx prisma migrate deploy
    npx prisma db seed
    echo "Release complete"

description: >
  A multi-component web application with
  a REST API, background workers, and
  a static frontend.

JSON is valid YAML

Any YAML 1.2 parser accepts JSON. If you prefer braces and quotes:

{
  "name": "my-app",
  "runtime": "node",
  "requires": ["postgres", "redis"],
  "commands": { "start": "node server.js" },
  "health": "/healthz"
}

This parses identically to the YAML equivalent. You can also mix styles — JSON inline for short values, YAML block for complex structures.