YAML vs JSON in CloudFormation: Key Differences and When to Use Each

In AWS CloudFormation, YAML and JSON are two formats to write infrastructure templates. YAML is more readable and concise, while JSON is more verbose but widely supported. Both produce the same infrastructure when deployed.

Quick Comparison

Here is a quick side-by-side comparison of YAML and JSON in CloudFormation templates.

Factor	YAML	JSON
Syntax Style	Indentation-based, clean and minimal	Braces and brackets, more punctuation
Readability	Easier for humans to read and write	More verbose and harder to scan
Support for Comments	Supports comments with #	No native comment support
File Size	Usually smaller due to less punctuation	Larger due to explicit syntax
Multi-document Support	Supports multiple documents in one file	Does not support multi-document
Error Detection	Indentation errors can be tricky	Syntax errors are explicit and strict

Key Differences

YAML uses indentation to show structure, making it look cleaner and easier to read, especially for complex templates. It allows comments anywhere using #, which helps explain parts of the template. This makes YAML popular for writing CloudFormation templates by hand.

JSON uses braces {} and brackets [] to define objects and arrays, requiring commas and quotes everywhere. It does not support comments, so explanations must be external. JSON is strict and less forgiving with syntax errors, which can help catch mistakes early.

Both formats describe the same CloudFormation resources and properties, so AWS treats them equally when deploying. The choice depends on your preference for readability and tooling support.

Code Comparison

Here is a simple CloudFormation template snippet that creates an S3 bucket, shown in YAML format.

yaml

AWSTemplateFormatVersion: '2010-09-09'
Resources:
  MyBucket:
    Type: 'AWS::S3::Bucket'
    Properties:
      BucketName: my-sample-bucket

Output

Creates an S3 bucket named 'my-sample-bucket'

JSON Equivalent

The same CloudFormation template in JSON format looks like this.

json

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Resources": {
    "MyBucket": {
      "Type": "AWS::S3::Bucket",
      "Properties": {
        "BucketName": "my-sample-bucket"
      }
    }
  }
}

Output

Creates an S3 bucket named 'my-sample-bucket'

When to Use Which

Choose YAML when you want easier-to-read templates, especially for large or complex infrastructure, and when you want to add comments directly in the file. It is great for manual editing and collaboration.

Choose JSON if you use tools or systems that generate or consume JSON automatically, or if you prefer strict syntax that helps catch errors early. JSON is also useful when integrating with other JSON-based workflows.

Key Takeaways

YAML is more readable and supports comments, making it ideal for manual CloudFormation templates.

JSON is more verbose and strict but widely supported and good for automated workflows.

Both YAML and JSON produce the same infrastructure when deployed by CloudFormation.

Choose YAML for clarity and ease of editing; choose JSON for strict syntax and tool compatibility.