YAML File Explained | Learn YML Format with Examples for Beginners

Home
DevOps
Understanding YAML Files: A Complete Guide for Beginners

DevOps

Understanding YAML Files: A Complete Guide for Beginners

Oct. 31, 2025 Amrit panta 27

YAML (short for “YAML Ain’t Markup Language”) is used widely across many technologies like Docker, Kubernetes, GitHub Actions, Ansible, Airflow, and CI/CD pipelines , to define configurations in a human-readable and structured way.

What is YAML?

YAML is a data serialization format, it’s used to represent data in a structured way (like JSON or XML), but much simpler and easier to read.

It’s indentation-based, meaning spaces define structure, not curly braces {} or square brackets []

Basic YAML Syntax Rules

Here are the core rules you must always remember:

Concept	Description	Example
Indentation	Use spaces, not tabs. Usually 2 spaces per level.	`key:` (2 spaces indentation for nested data)
Key-Value Pairs	Define data as `key: value`.	`name: Amrit`
Strings	Usually no need for quotes unless it contains special characters.	`city: Kathmandu`
Lists (Arrays)	Represented using `-` (dash and a space).	`fruits: <br>- apple<br>- banana`
Dictionaries (Objects)	Use indentation to define nested structures.	`person:<br> name: Amrit<br> age: 25`
Comments	Start with `#`.	`# This is a comment`
Booleans	Lowercase `true` / `false`.	`is_active: true`
Null Values	Use `null` or `~`.	`middle_name: null`

YAML vs JSON Example

Both define the same structure, but YAML is cleaner:

JSON

{
  "person": {
    "name": "Amrit",
    "age": 25,
    "skills": ["Python", "Django", "Odoo"]
  }
}

YAML

person:
  name: Amrit
  age: 25
  skills:
    - Python
    - Django
    - Odoo

Notice how YAML avoids braces {} and commas ,. Indentation defines hierarchy.

Advanced YAML Features

1.Nested Dictionaries (Objects)

server:
  host: localhost
  port: 8080
  credentials:
    username: admin
    password: secret

2.Lists of Dictionaries

employees:
  - name: Amrit
    role: Developer
    skills:
      - Python
      - Odoo
  - name: Pragya
    role: HR
    skills:
      - Communication
      - Management

3.Multi line string

description: |
  This is a multi-line
  text block. All newlines
  are preserved.

summary: >
  This is a folded block.
  Newlines are replaced
  with spaces.

| ? keeps newlines
> ? folds them into a single line

4.YAML in Real Projects (Practical Examples)

Example: Docker Compose (docker-compose.yml)

version: "3.8"
services:
  web:
    image: nginx:latest
    ports:
      - "8080:80"
  app:
    build: .
    depends_on:
      - db
  db:
    image: postgres:13
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass

Example: GitHub Actions Workflow (.github/workflows/deploy.yml)

name: Deploy to Server

on:
  push:
    branches:
      - main

jobs:
  deploy:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout Code
        uses: actions/checkout@v3

      - name: Run Deployment Script
        run: |
          echo "Deploying application..."
          ./deploy.sh

Tools to Help You Work with YAML

Online YAML Validator: https://yamlchecker.com/
VS Code Plugin: “YAML” (by Red Hat) — helps with autocomplete, linting, and validation.
YAML ? JSON converter: Many online tools exist (useful for debugging).