JSON, YAML, CSV, XML: When to Use Each Data Format

JSON — The API Standard

JSON (JavaScript Object Notation) is the dominant format for web APIs, configuration, and data exchange. It maps directly to native data structures in every major language.

{
  "user": {
    "id": 42,
    "name": "Jane Doe",
    "roles": ["admin", "editor"],
    "active": true
  }
}

Use JSON for: REST and GraphQL API responses, browser storage (localStorage/IndexedDB), configuration files in Node.js projects (package.json), inter-service communication.

Limitations: No comments, no multiline strings, verbose for tabular data, no schema enforcement without a separate tool (JSON Schema, Zod, etc.).

YAML — The Config File Champion

YAML is a superset of JSON (valid JSON is valid YAML) but adds human-friendly features: comments, multiline strings, anchors, and less punctuation.

user:
  id: 42
  name: Jane Doe
  roles:
    - admin
    - editor
  active: true
  # This is a comment
  bio: |
    Jane is a senior engineer.
    She leads the platform team.

Use YAML for: CI/CD configuration (GitHub Actions, GitLab CI, Kubernetes manifests), Docker Compose, Ansible playbooks, any config humans edit frequently.

Limitations: Whitespace-sensitive (indentation errors are hard to spot), the Norway problem (NO is parsed as boolean false in YAML 1.1), can be slow to parse for large data.

CSV — Tabular Data Exchange

CSV (Comma-Separated Values) is the universal format for tabular data — rows and columns with a header row.

id,name,role,active
42,Jane Doe,admin,true
43,John Smith,editor,false

Use CSV for: Data exports from databases, spreadsheet imports/exports, analytics data pipelines, anywhere non-technical users need to open data in Excel or Google Sheets.

Limitations: No nested structures, type system varies by parser, delimiter conflicts require quoting, no standard for encoding or line endings.

XML — The Enterprise Format

XML (eXtensible Markup Language) is verbose but self-describing and has a mature ecosystem for validation (XSD), querying (XPath/XQuery), and transformation (XSLT).

<user id="42">
  <name>Jane Doe</name>
  <roles>
    <role>admin</role>
    <role>editor</role>
  </roles>
  <active>true</active>
</user>

Use XML for: SOAP web services, RSS/Atom feeds, SVG, Microsoft Office documents (.docx, .xlsx are ZIP files containing XML), legacy enterprise integrations.

Limitations: Verbose, harder to read than JSON/YAML, slower to parse, no built-in array type (arrays are implied by repeated elements).

Quick Conversion Reference

// JSON to YAML (Node.js)
import { dump } from "js-yaml";
const yaml = dump(JSON.parse(jsonString));

// YAML to JSON
import { load } from "js-yaml";
const obj = load(yamlString);
const json = JSON.stringify(obj, null, 2);

// JSON to CSV (simple, flat objects)
const rows = JSON.parse(jsonString);
const headers = Object.keys(rows[0]).join(",");
const csv = [headers, ...rows.map(r => Object.values(r).join(","))].join("\n");

// CSV to JSON (basic)
const [header, ...lines] = csvString.split("\n");
const keys = header.split(",");
const json = lines.map(line =>
  Object.fromEntries(line.split(",").map((v, i) => [keys[i], v]))
);

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