YAML or JSON -- Which Format Should You Use?

YAML or JSON — Which Format Should You Use?

Both YAML and JSON represent structured data, and every YAML document is technically a superset of JSON — but they have very different ergonomics, tooling ecosystems, and failure modes. Here is when to choose each.

Quick decision rule

• Wire format / public API / data exchange → JSON
• Human-edited configuration (CI pipelines, Kubernetes, Ansible) → YAML (with a linter)
• Configs committed to version control where non-technical team members edit → YAML
• Configs loaded at runtime with strict schema validation → JSON (schema tooling is more mature)

YAML advantages

Readability: No quotes around simple strings, cleaner list syntax, and inline comments make YAML substantially more readable for humans writing configuration files.

# YAML — clean and readable
server:
  host: localhost
  port: 8080
  debug: true
tags:
  - web
  - api

// JSON — more verbose, no comments
{
  "server": {
    "host": "localhost",
    "port": 8080,
    "debug": true
  },
  "tags": ["web", "api"]
}

Supports comments: YAML allows # comments. JSON forbids them. For annotating configuration options, YAML wins.

Multi-line strings: YAML's block scalar operators (| for literal, > for folded) make embedding multi-line text natural.

YAML foot-guns

YAML's flexibility introduces parsing surprises:

Implicit type coercion:

• yes, no, on, off are parsed as booleans in YAML 1.1 (most common parsers). Write "yes" if you mean the string.
• 0777 is parsed as octal (511 decimal) in YAML 1.1. File permissions expressed as numbers must be quoted or written in decimal.
• Bare 1.0 is a float. 1 is an integer. Matters when strict typing is needed.

Norway problem: In YAML 1.1, NO is the boolean false. A country code list containing NO (Norway) breaks silently.

Anchors and aliases: YAML allows &anchor and *alias to reuse nodes — powerful but unfamiliar to many readers and not supported in JSON.

Indentation sensitivity: Unlike JSON's braces, YAML relies on whitespace. Tabs are forbidden; mixed indentation causes cryptic parse errors.

JSON advantages

• Strict grammar: no implicit types, no surprises
• Universal tooling: every language has a well-tested JSON parser in its standard library
• Schema validation: JSON Schema is widely adopted; YAML schema tooling is less mature
• Streaming-friendly: easier to parse as a stream without loading the full document

Interoperability

Because JSON is valid YAML, most YAML parsers can read JSON files directly. Converting the other way requires losing comments and may require quoting ambiguous values.

Round-trip and validate documents with the JSON ⇄ YAML converter and pretty-print JSON with the JSON Formatter.