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

Source: Dev.to

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.

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 stray character, or a trailing comma and the whole file breaks. 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 trailing zero!)

YAML’s implicit typing can cause 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.

Comment Support

JSON – No Official Comments

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

Developers resort to work‑arounds 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.

Language‑Specific Support

JSON – Universal

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

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

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

YAML – Widely Supported, Sometimes Problematic

# 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

# 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.

Real‑World Scenarios

APIs & Data Exchange

Winner: JSON

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

Configuration Files

YAML Example (simple):

app:
  name: MyApp
  port: 3000
  debug: true

TOML Example (complex):

[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

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

Package Management

JSON (package.json):

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

TOML (pyproject.toml):

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

[dependencies]
requests = "2.28.1"

Security

• JSON: Generally safe.

• YAML: Can be unsafe if arbitrary objects are deserialized. Example of a dangerous payload:

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

  Always use yaml.safe_load() in Python.

• TOML: Safe by design.

Winner: JSON and TOML are safe; YAML requires caution.

Decision Framework

Sample Projects

Converting Between Formats

JSON → YAML

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

becomes

name: John
age: 25

JSON → TOML

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

becomes

[database]
host = "localhost"
port = 5432

For quick conversions, try online tools such as jsontoall.tools, which handle JSON ↔ YAML, JSON ↔ TOML, and more.

Common Myths Debunked

The Future: What’s Next?

• JSON5 – A superset of JSON that adds comments, trailing commas, and more relaxed syntax.
• YAML 1.3 – Ongoing work to improve security and consistency.
• TOML 1.1 – Enhancements for richer data types and better tooling.

Happy configuring!

SON 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

• JSON is 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

Discussion

What format do you prefer and why? Drop a comment below – I’d love to hear about your experiences with these formats!

Tools

jsontoall.tools – instant JSON → YAML, JSON → TOML, and other conversions. All free, all browser‑based, zero sign‑up required.

Tags: #json #yaml #toml #webdev #configuration #devops #programming