JSON vs YAML vs TOML: Which Configuration Format Should You Use in 2026?

You're starting a new project. Time to create a config file. You open your editor and pause.
JSON? YAML? TOML? Which one?
Each format has passionate defenders. JSON fans praise its simplicity. YAML advocates love its readability. TOML supporters swear by its clarity.
But which one should YOU actually use? Let's settle this once and for all.

The Three Contenders at a Glance

Before we dive deep, here's the quick comparison:

JSON (JavaScript Object Notation)

Born: 2001
Used by: APIs, web configs, package managers
Famous for: Ubiquity and simplicity

YAML (YAML Ain't Markup Language)

Born: 2001
Used by: Docker, Kubernetes, CI/CD pipelines
Famous for: Human readability

TOML (Tom's Obvious, Minimal Language)

Born: 2013
Used by: Rust (Cargo), Python (Poetry), Hugo
Famous for: Clarity and minimal syntax

Now let's see how they actually stack up in real-world scenarios.

Round 1: Readability

Let's represent the same configuration in all three formats.
JSON

{
  "database": {
    "host": "localhost",
    "port": 5432,
    "credentials": {
      "username": "admin",
      "password": "secret123"
    },
    "pools": [
      {
        "name": "primary",
        "size": 10
      },
      {
        "name": "replica",
        "size": 5
      }
    ]
  }
}

YAML

database:
  host: localhost
  port: 5432
  credentials:
    username: admin
    password: secret123
  pools:
    - name: primary
      size: 10
    - name: replica
      size: 5

TOML

[database]
host = "localhost"
port = 5432

[database.credentials]
username = "admin"
password = "secret123"

[[database.pools]]
name = "primary"
size = 10

[[database.pools]]
name = "replica"
size = 5

Winner: YAML for simple configs, TOML for complex nested structures.
JSON's curly braces and quotes make it harder to scan quickly. YAML wins on minimal syntax, but TOML's explicit sections make complex configs clearer.

Round 2: Error Resistance

Here's where things get interesting.
JSON: Strict But Safe

{
  "name": "John",
  "age": 25,  // <- ERROR: No comments allowed
}  // <- ERROR: Trailing comma

JSON is unforgiving. One missing comma, one trailing comma, one stray character - your entire config breaks. But this strictness prevents ambiguity.
YAML: Flexible But Dangerous

name: John
age: 25
married: no  # Parsed as boolean false
country: NO  # Parsed as boolean false (Norway gets converted!)
version: 1.10  # Becomes float 1.1 (loses the zero!)

YAML's implicit typing causes silent bugs. That's not a config error - it's a logic bomb waiting to explode in production.
TOML: Clear and Predictable

name = "John"
age = 25
married = false  # Explicit boolean
country = "NO"   # Explicit string
version = "1.10" # Explicit string

TOML requires explicit types. No surprises, no implicit conversions.
Winner: TOML for reliability, JSON as close second. YAML is error-prone.

Round 3: Comments and Documentation

JSON: No Comments (Officially)

{
  "// This is a hack": "JSON doesn't support comments",
  "port": 8080,
  "_comment": "This is another workaround"
}

JSON has no official comment syntax. People resort to workarounds that pollute the data structure.
YAML: Full Comment Support

# This is a proper comment
port: 8080  # Inline comments work too

# You can document complex sections
database:
  host: localhost  # Override in production

TOML: Full Comment Support

# Server configuration
# Updated: 2025-01-15
port = 8080  # Default port

[database]
# Connection settings
host = "localhost"

Winner: Tie between YAML and TOML. Both support comments properly. JSON loses badly here.

Round 4: Tooling and Ecosystem

JSON: Universal Support
Every programming language has JSON parsing built-in. Every text editor syntax-highlights it. Every developer knows it.

// JavaScript (native)
const config = JSON.parse(data);

// Python (standard library)
import json
config = json.loads(data)

// Go (standard library)
var config Config
json.Unmarshal(data, &config)

YAML: Widely Supported, Sometimes Problematic
Most languages have YAML libraries, but they're often third-party and can have subtle differences.

# Python (requires PyYAML)
import yaml
config = yaml.safe_load(data)  # Note: safe_load, not load!

# JavaScript (requires js-yaml)
const yaml = require('js-yaml');
const config = yaml.load(data);

TOML: Growing Support
TOML is newer, so support varies. Major languages have good libraries now, but some obscure languages might not.

# Python (requires tomli for reading)
import tomli
config = tomli.loads(data)

# Rust (excellent support via serde)
let config: Config = toml::from_str(data)?;

Winner: **JSON **by a mile. YAML is second. TOML is catching up but not there yet.

Round 5: Use Case Performance

Let's see where each format actually shines in real-world scenarios.
APIs and Data Exchange
Winner: JSON
APIs need a format that works everywhere, is fast to parse, and has minimal ambiguity. JSON dominates here for good reason.

{
  "status": "success",
  "data": {
    "users": [...]
  }
}

Configuration Files
Winner: Depends on complexity
Simple configs (< 50 lines): YAML

app:
  name: MyApp
  port: 3000
  debug: true

Complex configs (50+ lines): TOML

[app]
name = "MyApp"
port = 3000
debug = true

[database.primary]
host = "localhost"
port = 5432

[database.replica]
host = "replica.example.com"
port = 5432

CI/CD Pipelines
Winner: YAML
GitHub Actions, GitLab CI, CircleCI all use YAML. The ecosystem has spoken.

name: Deploy
on: [push]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - run: npm install

Package Management
Winner: JSON for JavaScript, TOML for Rust/Python
package.json is ubiquitous:

{
  "name": "my-app",
  "dependencies": {
    "express": "^4.18.0"
  }
}

But Rust's Cargo.toml and Python's pyproject.toml show TOML winning mindshare in newer ecosystems:

[package]
name = "my-app"
version = "0.1.0"

[dependencies]
serde = "1.0"

Round 6: Security Considerations

JSON: Generally Safe
JSON is limited in what it can express. No code execution, no includes, no references. What you see is what you get.
YAML: Security Risks
YAML's flexibility is dangerous. The yaml.load() function can execute arbitrary Python code:

!!python/object/apply:os.system
args: ['rm -rf /']

Always use yaml.safe_load() in Python. Many developers don't know this.
TOML: Safe by Design
TOML is simple enough that there's no execution risk. It's just data.
Winner: JSON and TOML are safe. YAML requires caution.

The Verdict: Which Should You Choose?

Here's my decision framework:
Choose JSON if:

✅ You're building an API
✅ You need universal compatibility
✅ You're exchanging data between systems
✅ You want the fastest parsing speed
✅ Your configs are simple (< 20 lines)

Example use cases:

REST API responses
Configuration files for simple apps
Data serialization
Package.json files

Choose YAML if:

✅ You're writing CI/CD configs (GitHub Actions, GitLab CI)
✅ You're configuring Docker/Kubernetes
✅ Human readability is critical
✅ You need extensive comments
✅ Your team already uses YAML everywhere

Example use cases:

Docker Compose files
Kubernetes manifests
GitHub Actions workflows
Ansible playbooks

Choose TOML if:

✅ You're writing application config files
✅ Your config is complex and nested
✅ You need explicit typing
✅ You want to avoid YAML's gotchas
✅ You're building a Rust or modern Python project

Example use cases:

Cargo.toml (Rust packages)
pyproject.toml (Python projects)
Hugo site configs
Application settings files

Real-World Recommendations by Project Type

Web Application
Config file: TOML
API responses: JSON
Docker setup: YAML
CLI Tool
Config file: TOML or JSON
API calls: JSON
DevOps Pipeline
Everything: YAML (for consistency with CI/CD)
Library/Package
JavaScript: JSON (package.json)
Python: TOML (pyproject.toml)
Rust: TOML (Cargo.toml)

Converting Between Formats

Need to switch formats? Here's how:
JSON to YAML

{"name": "John", "age": 25}

becomes:

name: John
age: 25

JSON to TOML

{"database": {"host": "localhost", "port": 5432}}

becomes:

[database]
host = "localhost"
port = 5432

For quick conversions between formats, you can use tools like jsontoall.tools which handles JSON to YAML, JSON to TOML, and other format conversions instantly in your browser.

Common Myths Debunked
Myth 1: "YAML is always more readable than JSON"
False. For simple, flat structures, JSON is fine:

{"debug": true, "port": 3000}

vs

debug: true
port: 3000

The difference is minimal.
Myth 2: "TOML can't handle complex nesting"
False. TOML handles nesting well with table syntax:

[servers.alpha]
ip = "10.0.0.1"

[servers.alpha.database]
host = "localhost"

Myth 3: "JSON doesn't support comments because it's bad design"
Debatable. Douglas Crockford removed comments to prevent people from putting parsing directives in JSON files. It was intentional, not an oversight.
The Future: What's Next?
JSON5 is gaining traction. It's JSON with comments, trailing commas, and other nice-to-haves:

{
  name: "John",  // Comments work!
  age: 25,       // Trailing comma is fine
}

JSON Schema is becoming important for validation:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "properties": {
    "age": {"type": "integer", "minimum": 0}
  }
}

YAML 1.2 fixed some issues from 1.1, but adoption is slow.
Final Thoughts
There's no universal winner. Each format excels in different scenarios:

JSONis the safe, universal choice for data exchange
YAML wins for DevOps and CI/CD where it's already standard
TOML is best for application configuration files

My personal stack in 2026:

APIs: JSON
CI/CD: YAML (because that's what the tools use)
App configs: TOML
Package files: Whatever the ecosystem uses (package.json, Cargo.toml, etc.)
Stop arguing about which format is "better." Use the right tool for the job.

What format do you prefer and why? Drop a comment below - I'd love to hear about your experiences with these formats!
Need to convert between formats? Check out jsontoall.tools for instant JSON to YAML, JSON to TOML, and other conversions. All free, all browser-based, zero sign-up required.
Tags: #json #yaml #toml #webdev #configuration #devops #programming