JSON to CSV Converter — Developer Code Samples

Convert JSON arrays of objects to CSV format for spreadsheets, data analysis, and ETL pipelines. Python's csv module and json module together handle this conversion without any external dependencies. jq is the command-line tool of choice for shell pipelines.

Try the interactive version online: Open JSON to CSV Converter Tool →

Parameters

Parameter	Type	Required	Description
json_string	str	Yes	JSON string containing an array of objects
delimiter	str	No	Field separator character (default: comma)
include_headers	bool	No	Include header row with column names (default: True)

Returns: CSV-formatted string with header row and data rows

Code Examples

import json
import csv
import io

def json_to_csv(json_string, delimiter=','):
    """Convert a JSON array of objects to CSV string."""
    data = json.loads(json_string)

    if not data:
        return ""

    # Handle both array and object with array value
    if isinstance(data, dict):
        # Find first array value
        for v in data.values():
            if isinstance(v, list):
                data = v
                break

    if not isinstance(data, list):
        raise ValueError("JSON must be an array of objects")

    # Collect all keys (headers) in order of first appearance
    headers = []
    seen = set()
    for row in data:
        if isinstance(row, dict):
            for k in row.keys():
                if k not in seen:
                    headers.append(k)
                    seen.add(k)

    # Write CSV to string buffer
    output = io.StringIO()
    writer = csv.DictWriter(output, fieldnames=headers, delimiter=delimiter,
                            extrasaction='ignore', lineterminator='\n')
    writer.writeheader()
    writer.writerows(data)
    return output.getvalue()

# Example
json_data = '''[
    {"name": "Alice", "age": 30, "city": "New York"},
    {"name": "Bob", "age": 25, "city": "London"},
    {"name": "Carol", "age": 35, "city": "Tokyo"}
]'''

csv_output = json_to_csv(json_data)
print(csv_output)
# Output:
# name,age,city
# Alice,30,New York
# Bob,25,London
# Carol,35,Tokyo

# Write to file
with open('output.csv', 'w', newline='', encoding='utf-8') as f:
    f.write(csv_output)

// Convert JSON array to CSV
function jsonToCSV(jsonString, delimiter = ',') {
  const data = typeof jsonString === 'string' ? JSON.parse(jsonString) : jsonString;

  if (!Array.isArray(data) || data.length === 0) return '';

  // Collect all unique headers in order
  const headers = [...new Set(data.flatMap(row => Object.keys(row)))];

  // Escape a CSV cell value
  function escapeCell(value) {
    if (value == null) return '';
    const str = String(value);
    if (str.includes(delimiter) || str.includes('"') || str.includes('\n')) {
      return '"' + str.replace(/"/g, '""') + '"';
    }
    return str;
  }

  // Build CSV rows
  const rows = [
    headers.map(h => escapeCell(h)).join(delimiter),
    ...data.map(row =>
      headers.map(h => escapeCell(row[h] ?? '')).join(delimiter)
    )
  ];

  return rows.join('\n');
}

const jsonData = [
  { name: "Alice", age: 30, city: "New York" },
  { name: "Bob", age: 25, city: "London" },
  { name: "Carol", age: 35, city: "Tokyo" }
];

const csv = jsonToCSV(jsonData);
console.log(csv);
// Output:
// name,age,city
// Alice,30,New York
// Bob,25,London
// Carol,35,Tokyo

// Download as file in browser
function downloadCSV(csv, filename = 'data.csv') {
  const blob = new Blob([csv], { type: 'text/csv;charset=utf-8;' });
  const url = URL.createObjectURL(blob);
  const a = document.createElement('a');
  a.href = url; a.download = filename; a.click();
}

# Convert JSON array to CSV using jq
echo '[{"name":"Alice","age":30},{"name":"Bob","age":25}]' | \
  jq -r '(.[0] | keys_unsorted) as $keys | $keys, (.[] | [.[$keys[]]] | @csv)' | \
  awk 'NR==1{gsub(/"/, ""); print} NR>1{print}'

# Convert JSON file to CSV
jq -r '(.[0] | keys_unsorted) as $k | [$k[]], (.[] | [.[$k[]]]) | @csv' data.json > output.csv

# With Python (no dependencies)
python3 -c "
import json, csv, sys
data = json.load(sys.stdin)
if data:
    w = csv.DictWriter(sys.stdout, fieldnames=data[0].keys())
    w.writeheader()
    w.writerows(data)
" < data.json > output.csv

# Using miller (mlr) for complex transformations
mlr --json --ocsv cat data.json > output.csv

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