YAML vs JSON: Which Should You Use?

Every developer eventually faces this question: should I use YAML or JSON for this config file? The answer, like most things in software, is "it depends." But after years of dealing with both formats across dozens of projects, I've developed some strong opinions.

Let me share what I've learned so you can make the right choice for your specific situation.

The Quick Answer

If you're in a hurry, here's the TL;DR:

• Use JSON for APIs, data exchange, and anything machines will read
• Use YAML for configuration files that humans will edit frequently

But if you want to understand why, keep reading.

A Tale of Two Formats

JSON (JavaScript Object Notation) was born from JavaScript in the early 2000s. It was designed to be a lightweight data format that was easy for both humans and machines to read. And it succeeded: JSON became the de facto standard for web APIs.

YAML (YAML Ain't Markup Language) came along with a different goal: maximum human readability. It uses indentation instead of brackets, supports comments, and has a cleaner syntax for complex nested structures.

Let's see the same data in both formats:

JSON:

{
  "server": {
    "host": "localhost",
    "port": 3000,
    "ssl": {
      "enabled": true,
      "certificate": "/path/to/cert.pem"
    }
  },
  "database": {
    "url": "postgres://localhost:5432/myapp",
    "pool_size": 10
  }
}

YAML:

# Server configuration
server:
  host: localhost
  port: 3000
  ssl:
    enabled: true
    certificate: /path/to/cert.pem

# Database configuration
database:
  url: postgres://localhost:5432/myapp
  pool_size: 10

The YAML version is more readable at a glance. The comments explain what each section does. There's no visual noise from brackets and quotes. For a config file that developers will edit regularly, this matters.

Where JSON Wins

APIs and Data Exchange

JSON is the king of web APIs, and for good reason. It's supported natively in every programming language, parses quickly, and has a strict specification that leaves no room for ambiguity.

When you're building a REST API, use JSON. When you're storing data in a document database, use JSON. When you're exchanging data between services, use JSON.

The strict syntax that some people find annoying is actually a feature here. There's only one way to represent data in JSON, which means fewer parsing surprises.

Browser Environments

JavaScript can parse JSON natively with JSON.parse(). It's fast, it's built-in, and it just works. YAML requires a library, which means extra bytes to download and potential compatibility issues.

When Strictness is a Feature

JSON's pickiness can save you from subtle bugs. Trailing commas? Error. Duplicate keys? The parser will tell you. YAML is more forgiving, which sounds nice until you spend an hour debugging a config file where you accidentally defined the same key twice and the second value silently overwrote the first.

Where YAML Wins

Configuration Files

This is YAML's home turf. If you've used Docker Compose, Kubernetes, GitHub Actions, or Ansible, you've written YAML. These tools chose YAML because their config files are read and edited by humans far more often than machines.

Consider a GitHub Actions workflow:

name: CI Pipeline
on:
  push:
    branches: [main]
  pull_request:
    branches: [main]
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      
      - name: Setup Node.js
        uses: actions/setup-node@v3
        with:
          node-version: '18'
          
      - name: Install dependencies
        run: npm ci
        
      - name: Run tests
        run: npm test

This is remarkably readable. You can understand what this workflow does at a glance. Now imagine this in JSON, with all the brackets and quotes and no comments. It would work, but it would be harder to write and maintain.

Comments Are Essential

JSON doesn't support comments. Full stop. This is by design: Douglas Crockford removed them because people were using comments to hold parsing directives, which defeated the purpose of a simple data format.

But for configuration files, comments are essential. You need to explain why a setting exists, not just what it is:

# Increase this if you see "too many connections" errors
# Default is 10, we bumped it for the Black Friday traffic spike
pool_size: 50

Good luck adding context like that in JSON.

Multi-line Strings

YAML handles multi-line strings gracefully:

description: |
  This is a long description
  that spans multiple lines.
  
  It even preserves blank lines
  and formatting.

In JSON, you'd need to escape newlines or use an array of strings and join them. Neither is pleasant.

The Dark Side of YAML

I'd be doing you a disservice if I didn't mention YAML's gotchas. Because there are many.

The Whitespace Problem

YAML uses indentation for structure, and it's unforgiving about it. Mix tabs and spaces? Broken. Inconsistent indentation? Broken. Invisible trailing whitespace? Potentially broken.

# This works
server:
  port: 3000

# This is broken (tab instead of spaces)
server:
	port: 3000

The worst part? These errors can be invisible. Your editor might show what looks like correct indentation while the file contains tabs that YAML rejects.

Pro tip: When your YAML isn't parsing and you can't figure out why, convert it to JSON first. If the conversion fails, you've got a syntax error. If it succeeds, the problem is elsewhere. Try our YAML ↔ JSON Converter to debug quickly.

The Norway Problem

Here's a fun one. In YAML, certain strings are automatically interpreted as booleans:

# You might expect these to be strings...
country: NO      # Parsed as boolean false!
enabled: yes     # Parsed as boolean true!
answer: off      # Parsed as boolean false!

Yes, NO (the ISO country code for Norway) is parsed as boolean false in YAML. This has caused real bugs in real production systems. Always quote strings that could be misinterpreted:

country: "NO"    # Now it's a string

Implicit Type Conversion

YAML tries to be helpful by automatically converting values to appropriate types. Sometimes this helps. Sometimes it causes chaos:

version: 1.0     # Float
version: "1.0"   # String
version: 1.10    # Float (1.1, not "1.10"!)
port: 0777       # Octal! (511 in decimal)

Always quote values when you need them to be strings, especially version numbers and anything that looks like it could be a number.

Making the Choice

Here's my decision framework:

Choose JSON when:

• Building or consuming APIs
• Storing data in databases
• Working in browser JavaScript
• Strict parsing is important
• The file is mostly read by machines

Choose YAML when:

• Writing configuration files
• Humans will edit the file regularly
• You need comments
• Readability is the top priority
• Using tools that expect YAML (Docker, K8s, etc.)

Converting Between Formats

Sometimes you need to convert between formats. maybe you want to validate a YAML file by seeing if it parses correctly, or you're migrating from one format to another.

Our YAML ↔ JSON Converter handles both directions, preserves key order, and supports multi-document YAML files. It's useful for debugging too: if your YAML won't convert to JSON, you've got a syntax error somewhere.

For formatting and validating JSON specifically, check out our JSON Formatter.

The Bottom Line

There's no universally "better" format. JSON and YAML each have their place. JSON is more robust for data exchange, YAML is more pleasant for configuration.

The real skill is knowing which tool to use for which job. And now you do.

Tools mentioned in this article:

• YAML ↔ JSON Converter. Convert between formats
• JSON Formatter. Format and validate JSON