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YAML Basics

Quick reference for writing YAML configuration files.

Basic Syntax

YAML Meaning
key: value Assign a value
- item List item
# comment Comment (ignored)
"string" Explicit string (use quotes if value has special chars)
- Indentation (use spaces, not tabs)

Data Types

Strings

name: hello        # No quotes needed
message: "hello world"  # Quotes for special chars

Numbers

count: 42         # Integer
price: 19.99      # Float

Booleans

enabled: true   # or yes, on
disabled: false # or no, off

Lists

# Inline syntax
colors: [red, green, blue]

# Block syntax
colors:
  - red
  - green
  - blue

Dictionaries

# Inline syntax
server: {host: localhost, port: 8080}

# Block syntax
server:
  host: localhost
  port: 8080

Indentation Rules

  • Use spaces (not tabs)
  • Consistent indentation (usually 2 spaces)
  • Nested items are indented further
parent:
  child:
    grandchild: value

Common Patterns in DQM-ML

Key-Value Pairs

dataloaders:
  loaders:
    - name: my_data
      type: parquet
      path: data/train.parquet

Lists of Options

metrics:
  processors:
    - name: completeness
      type: completeness
      columns:
        input:
          - name
          - age
          - score

Nested Configuration

features:
  processors:
    - name: image_embedding
      type: features_embeddings
      model:
        arch: resnet18
      infer:
        batch_size: 10
        width: 224

Common Mistakes to Avoid

Wrong: Using Tabs

# Wrong — uses tabs (shown as →)
key:→value

# Correct — uses spaces (shown as ·)
key:.value

Wrong: Inconsistent Indentation

# Wrong — key2 indented inconsistently
key1: value
··key2: value    # ← 2 extra spaces (shown as ..), wrong level

# Correct — consistent indentation
key1: value
key2: value

Wrong: Missing Colon

# Wrong - missing colon after key
key value

# Correct
key: value

Tools for Writing YAML

  • YAML Validator - Check syntax
  • Visual Studio Code: extension YAML by Red Hat

Yaml validation

Add on top of your configuration: 

# yaml-language-server: $schema=docs/schema/config.json

You might need to update the link to the schema, relative to your configuration file, or absolute.