Creates a YAML description from a JSON payload (replace $data by your JSON payload)

json2yamldesc.php

<?php

function formatLine(array $items, $indent)
{
    $spaces = '';
    while ($indent--) {
        $spaces .= ' ';
    }
    return PHP_EOL .
        implode(PHP_EOL,
            array_map(function ($item) use ($spaces) {
                return $spaces . $item;
            }, $items))
        . PHP_EOL;
}

function getFormatter($key, $value, $indent = 0)
{
    $keyLine = null !== $key ? $key . ':' : '';

    switch ($type = gettype($value)) {
        case 'double':
            echo formatLine([
                $keyLine,
                '  type: number',
                '  format: float',
                '  example: ' . $value
            ], $indent);
            break;
        case 'integer':
            echo formatLine([
                $keyLine,
                '  type: number',
                '  example: ' . $value
            ], $indent);
            break;
        case 'string':
            echo formatLine([
                $keyLine,
                '  type: string',
                '  example: "' . $value . '"'
            ], $indent);
            break;
        case 'boolean':
            echo formatLine([
                $keyLine,
                '  type: boolean',
                '  example: ' . (string)$value
            ], $indent);
            break;
        case 'object':
            echo formatLine([
                $keyLine,
                '  type: object',
                '  properties: ',
            ], $indent);
            foreach ($value as $key2 => $value2) {
                getFormatter($key2, $value2, $indent + 4);
            }
            break;
        case 'array':
            $lineItems = [
                $keyLine,
                '  type: array'
            ];
            if (count($value)) {
                $lineItems[] = '  items: ';
            }
            echo formatLine($lineItems, $indent);
            $oldKey = PHP_INT_MAX;
            foreach ($value as $key2 => $value2) {
                $finalKey = is_int($key2) ? null : $key2;
                if ($finalKey !== $oldKey) {
                    getFormatter($finalKey, $value2, $indent + 2);
                    $oldKey = $finalKey;
                }
            }
            break;
        default:
            throw new Exception($type . ' unknown');
    }
}

function toYaml($data)
{
    foreach ($data as $key => $value) {
        getFormatter($key, $value);
    }
}

$data = <<<JSON
{
  "string": "abcd",
  "integer": 123,
  "array": [1,2,3],
  "object": {
    "string": "abcd",
    "integer": 123,
    "array": [1, 2, 3]
  }
}
JSON;

toYaml(json_decode($data));

The gist returns:

string:
  type: string
  example: "abcd"

integer:
  type: number
  example: 123

array:
  type: array
  items: 

  
    type: number
    example: 1

object:
  type: object
  properties: 

    string:
      type: string
      example: "abcd"

    integer:
      type: number
      example: 123

    array:
      type: array
      items: 

      
        type: number
        example: 1