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YAML and JSON — when to use each

YAML vs. JSON: complementary formats for different contexts

JSON (JavaScript Object Notation) is the lingua franca of web APIs — compact, universally supported, and trivially parseable in every programming language. It excels in data interchange between services, API payloads, and configuration that needs to be read by machines first and humans second.

YAML (YAML Ain't Markup Language) is a superset of JSON that prioritizes human readability. Its indentation-based structure, support for comments, multi-line strings, and anchors make it a natural fit for configuration files that developers read and edit frequently — Kubernetes manifests, GitHub Actions workflows, Docker Compose files, and Ansible playbooks. The ability to convert freely between the two formats is essential when integrating tools that expect one format with systems that produce the other.

When to use YAML

Kubernetes, Helm charts, and Docker Compose
GitHub Actions, GitLab CI, and Jenkins pipelines
Ansible playbooks and Salt states
Any config file a human edits regularly

When to use JSON

REST API request and response bodies
Package manifests: package.json, composer.json
Design tokens and configuration for tools
Any data consumed by JavaScript directly

100% private & client-side

YAML parsed with a pure-JS parser — no server calls
Safe for Kubernetes secrets, tokens, and credentials
Zero data transmitted to any server
Works offline after initial page load

How to use this tool

Choose direction: YAML → JSON or JSON → YAML
Paste or upload your file — auto-converts as you type
Use Swap to flip input/output instantly
Copy or download result as .json / .yaml

YAML pitfalls to avoid

Tabs are forbidden — always use spaces for indentation
yes/no are booleans, not strings — quote them if needed
Norway problem: NO parses as false in YAML 1.1
Dates like 2024-01-01 become strings in JSON output

Output formatting options

Pretty — indented JSON, easy to read and review
Minified — compact JSON, ideal for API responses
Both formats are semantically identical
Copy or download the result with one click

Important differences between YAML and JSON

While YAML is technically a superset of JSON (valid JSON is also valid YAML), there are important gotchas when converting. YAML supports comments (# comment) which are lost when converting to JSON. YAML anchors (&anchor) and aliases (*alias) allow reusing content — these get expanded on conversion. YAML has several additional scalar types: dates (2024-01-01 becomes a string in JSON), nulls can be written as ~ or null, and booleans accept yes/no/on/off as values (a common source of bugs in Kubernetes configs).