JSON to YAML Converter: Convert Between Formats Instantly

import yaml from 'js-yaml'

// ── JSON to YAML ──────────────────────────────────────────────
function jsonToYaml(jsonString: string, indent = 2): string {
  // Parse JSON first to validate syntax
  const data = JSON.parse(jsonString)
  return yaml.dump(data, {
    indent,             // indentation (default: 2 spaces)
    lineWidth: 120,     // wrap long strings at 120 chars (-1 = never wrap)
    noRefs: true,       // disable anchor generation (keep output simple)
    sortKeys: false,    // preserve key order from JSON
    quotingType: '"',   // use double quotes for strings that need quoting
  })
}

// ── YAML to JSON ──────────────────────────────────────────────
function yamlToJson(yamlString: string, pretty = true): string {
  // yaml.load() parses the first YAML document
  const data = yaml.load(yamlString)
  return JSON.stringify(data, null, pretty ? 2 : 0)
}

// ── Handle multi-document YAML ────────────────────────────────
function yamlMultiDocToJsonArray(yamlString: string): string {
  // yaml.loadAll() handles --- separated documents
  const documents: unknown[] = []
  yaml.loadAll(yamlString, (doc) => { documents.push(doc) })
  return JSON.stringify(documents, null, 2)
}

// ── Example ───────────────────────────────────────────────────
const json = JSON.stringify({
  apiVersion: 'apps/v1',
  kind: 'Deployment',
  metadata: { name: 'web-app', labels: { version: '1.10' } },
  spec: { replicas: 3 },
}, null, 2)

console.log(jsonToYaml(json))
// apiVersion: apps/v1
// kind: Deployment
// metadata:
//   name: web-app
//   labels:
//     version: '1.10'
// spec:
//   replicas: 3

import json
import yaml
from io import StringIO

# ── PyYAML (most common, YAML 1.1 semantics) ──────────────────
def json_to_yaml_pyyaml(json_string: str) -> str:
    data = json.loads(json_string)
    return yaml.dump(
        data,
        default_flow_style=False,  # block style (NOT inline)
        allow_unicode=True,        # don't escape Unicode as \uXXXX
        sort_keys=False,           # preserve JSON key order
        indent=2,
    )

def yaml_to_json_pyyaml(yaml_string: str, pretty: bool = True) -> str:
    data = yaml.safe_load(yaml_string)  # safe_load, never yaml.load(untrusted)
    return json.dumps(data, indent=2 if pretty else None, ensure_ascii=False)

# ── ruamel.yaml (YAML 1.2, preserves comments on round-trip) ──
from ruamel.yaml import YAML

def json_to_yaml_ruamel(json_string: str) -> str:
    """
    Use ruamel.yaml when you need YAML 1.2 semantics:
    - NO implicit boolean coercion (yes/no stay as strings)
    - Preserves comments when round-tripping existing YAML files
    """
    data = json.loads(json_string)
    ryaml = YAML()
    ryaml.default_flow_style = False
    ryaml.indent(mapping=2, sequence=4, offset=2)
    stream = StringIO()
    ryaml.dump(data, stream)
    return stream.getvalue()

# ── Multi-document YAML → JSON array ─────────────────────────
def yaml_multidoc_to_json(yaml_string: str) -> str:
    documents = list(yaml.safe_load_all(yaml_string))
    return json.dumps(documents, indent=2, ensure_ascii=False)

# ── CLI usage with Python stdlib ──────────────────────────────
# python3 -c "
# import json, yaml, sys
# print(yaml.dump(json.load(sys.stdin), default_flow_style=False))
# " < input.json > output.yaml

package main

import (
    "encoding/json"
    "fmt"

    "gopkg.in/yaml.v3"
)

// JSONToYAML converts JSON bytes to YAML bytes
func JSONToYAML(jsonBytes []byte) ([]byte, error) {
    // Parse JSON into generic interface{}
    var data interface{}
    if err := json.Unmarshal(jsonBytes, &data); err != nil {
        return nil, fmt.Errorf("JSON parse error: %w", err)
    }

    // Convert numbers: json.Unmarshal uses float64 for all numbers
    // yaml.Marshal preserves them correctly
    return yaml.Marshal(data)
}

// YAMLToJSON converts YAML bytes to JSON bytes
func YAMLToJSON(yamlBytes []byte) ([]byte, error) {
    var data interface{}
    if err := yaml.Unmarshal(yamlBytes, &data); err != nil {
        return nil, fmt.Errorf("YAML parse error: %w", err)
    }

    // yaml.v3 uses map[string]interface{} for objects and []interface{} for arrays
    // — compatible with encoding/json
    return json.MarshalIndent(data, "", "  ")
}

func main() {
    jsonInput := `{"name": "web-app", "replicas": 3, "tags": ["app", "web"]}`
    yamlOutput, err := JSONToYAML([]byte(jsonInput))
    if err != nil {
        panic(err)
    }
    fmt.Printf("%s", yamlOutput)
    // name: web-app
    // replicas: 3
    // tags:
    //   - app
    //   - web
}

# YAML 1.1 coercions that break YAML → JSON conversion

# ── Boolean coercions (the "Norway Problem") ──────────────────
country: NO         # → false  (YAML 1.1 booleans: y/n/yes/no/true/false/on/off)
country: "NO"       # → "NO"   (safe: quoted)
env: ON             # → true
active: Yes         # → true
enabled: FALSE      # → false

# ── Octal numbers ─────────────────────────────────────────────
mode: 0755          # → 493    (octal in YAML 1.1)
mode: "0755"        # → "0755" (safe: quoted)

# ── Floats from version strings ───────────────────────────────
version: 1.10       # → 1.1    (float — trailing zero dropped!)
version: "1.10"     # → "1.10" (safe: quoted)
api_version: 1.0    # → 1.0    (float, displays as 1.0 in JSON but lost precision)

# ── Infinity and NaN (not valid JSON) ─────────────────────────
score: .inf         # → Infinity  → JSON serialization fails: not a valid JSON number
value: .nan         # → NaN       → JSON serialization fails

# ── Null coercions ────────────────────────────────────────────
key:                # → null   (empty value)
key: ~              # → null
key: null           # → null   (both YAML 1.1 and 1.2)

# ── YAML 1.2 (ruamel.yaml, YAML 1.2 parsers) ─────────────────
# YAML 1.2 removes all the above ambiguities:
# - Only true/false are booleans (case-sensitive, lowercase only)
# - No octal 0755 coercion (0o755 is octal in YAML 1.2)
# - NO/YES/ON/OFF are plain strings
# - Floats must be explicit: 1.0 is float, 1 is integer

import yaml
import json

def yaml_to_json_safe(yaml_string: str) -> str:
    """
    Convert YAML to JSON with coercion detection.
    Warns when YAML 1.1 coercions change the semantic meaning.
    """
    data = yaml.safe_load(yaml_string)

    # Detect Infinity/NaN before JSON serialization
    def check_json_safe(obj, path=""):
        import math
        if isinstance(obj, float):
            if math.isinf(obj) or math.isnan(obj):
                raise ValueError(
                    f"Cannot convert {path}: {obj} is not valid JSON. "
                    f"Quote it in YAML: {path.split('.')[-1]}: ".inf""
                )
        elif isinstance(obj, dict):
            for k, v in obj.items():
                check_json_safe(v, f"{path}.{k}")
        elif isinstance(obj, list):
            for i, v in enumerate(obj):
                check_json_safe(v, f"{path}[{i}]")

    check_json_safe(data)
    return json.dumps(data, indent=2, ensure_ascii=False)

# YAML with anchors and merge key (<<)
defaults: &defaults
  image: node:20-alpine
  restart: unless-stopped
  env:
    NODE_ENV: production

services:
  api:
    <<: *defaults          # merge all keys from defaults
    ports: ["3000:3000"]
    command: ["node", "api/server.js"]

  worker:
    <<: *defaults          # reuse same defaults
    ports: []
    command: ["node", "worker/index.js"]

# ── After conversion to JSON (anchors expanded) ─────────────────
{
  "defaults": {
    "image": "node:20-alpine",
    "restart": "unless-stopped",
    "env": { "NODE_ENV": "production" }
  },
  "services": {
    "api": {
      "image": "node:20-alpine",       // repeated
      "restart": "unless-stopped",     // repeated
      "env": { "NODE_ENV": "production" },  // repeated
      "ports": ["3000:3000"],
      "command": ["node", "api/server.js"]
    },
    "worker": {
      "image": "node:20-alpine",       // repeated again
      "restart": "unless-stopped",
      "env": { "NODE_ENV": "production" },
      "ports": [],
      "command": ["node", "worker/index.js"]
    }
  }
}

# ── yq (most popular YAML CLI tool) ─────────────────────────
# yq: handles YAML, JSON, TOML, XML. 7,000+ GitHub stars.
# brew install yq  /  snap install yq  /  go install github.com/mikefarah/yq/v4@latest

# JSON to YAML
yq -P input.json                          # -P = prettyprint as YAML
yq eval . input.json -o yaml > output.yaml

# YAML to JSON
yq eval . input.yaml -o json > output.json

# Pretty-print JSON as YAML
echo '{"name":"app","replicas":3}' | yq -P

# ── Python one-liners (no additional packages for basic cases) ─
# JSON → YAML
python3 -c "import sys,json,yaml; print(yaml.dump(json.load(sys.stdin), default_flow_style=False))" < in.json

# YAML → JSON
python3 -c "import sys,json,yaml; print(json.dumps(yaml.safe_load(sys.stdin), indent=2))" < in.yaml

# ── jq + yq pipeline ─────────────────────────────────────────
# Transform JSON and convert to YAML in one pipeline
jq '.spec.template.spec.containers[] | {name, image}' deploy.json | yq -P

# ── Node.js one-liner ─────────────────────────────────────────
# node -e "const yaml=require('js-yaml'),fs=require('fs');
#   console.log(yaml.dump(JSON.parse(fs.readFileSync('/dev/stdin','utf8'))))" < in.json