Convert Nested JSON to CSV Online Free – Fast JSON to CSV Converter (Handles Arrays & Large Files)

Best JSON to CSV Converter Online – Convert Complex JSON (Nested + Arrays) to CSV

Struggling to convert complex JSON into a clean, usable CSV file? This advanced JSON to CSV converter lets you instantly transform nested JSON, arrays, and structured data into CSV format—right in your browser. Unlike basic tools, it automatically flattens nested objects, handles arrays intelligently, and processes data securely without uploading anything to a server . Designed for speed and reliability, this tool supports files up to 1MB for instant conversion , making it perfect for developers, analysts, and anyone working with API or structured data.

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.small { font-size: 13px; color: #666; margin-top: 5px; } JSON to CSV Converter Convert nested JSON into CSV instantly in your browser. Max file size: 1MB .

Convert Download CSV Copy CSV let csvOutput = ""; let parsedRows = []; let allFields = [];

const MAX_SIZE = 1 * 1024 * 1024; // 1MB

document.getElementById(“fileInput”).addEventListener(“change”, function(e) { const file = e.target.files[0]; if (!file) return;

if (file.size > MAX_SIZE) { showMsg(“File exceeds 1MB limit.”, “red”); e.target.value = ""; return; }

const reader = new FileReader(); reader.onload = function(evt) { document.getElementById(“jsonInput”).value = evt.target.result; showMsg(“File loaded successfully.”, “green”); }; reader.readAsText(file); });

function showMsg(text, color=“red”) { const msg = document.getElementById(“msg”); msg.style.color = color; msg.innerText = text; }

function convertJSON() { let input = document.getElementById(“jsonInput”).value;

if (new Blob([input]).size > MAX_SIZE) { showMsg(“Input exceeds 1MB limit.”, “red”); return; }

try { let data = JSON.parse(input); if (!Array.isArray(data)) data = [data];

parsedRows = data.map(obj => flatten(obj)); allFields = […new Set(parsedRows.flatMap(o => Object.keys(o)))];

generateCSV(); renderPreview();

showMsg(“Converted successfully”, “green”);

} catch (e) { showMsg(“Invalid JSON: ” + e.message); } }

function flatten(obj, prefix="", res={}) { for (let key in obj) { let val = obj[key]; let newKey = prefix ? prefix + ”.” + key : key;

if (typeof val === “object” && val !== null && !Array.isArray(val)) { flatten(val, newKey, res); } else if (Array.isArray(val)) { res[newKey] = val.map(v => typeof v === “object” ? JSON.stringify(v) : v).join(”, ”); } else { res[newKey] = val; } } return res; }

function generateCSV() { let rows = []; rows.push(allFields.join(”,”));

parsedRows.forEach(r => { rows.push(allFields.map(f => "${(r[f]||"").toString().replace(/"/g,'""')}").join(”,”)); });

csvOutput = rows.join(“\n”); }

function renderPreview() { let html = “<table><tr>”; allFields.forEach(f => html += “<th>“+f+”</th>”); html += ”</tr>”;

parsedRows.slice(0,20).forEach(r => { html += “<tr>”; allFields.forEach(f => html += “<td>”+(r[f]||"")+”</td>”); html += ”</tr>”; });

html += ”</table>”; document.getElementById(“preview”).innerHTML = html; }

function downloadCSV() { let blob = new Blob([csvOutput], {type:“text/csv”}); let a = document.createElement(“a”); a.href = URL.createObjectURL(blob); a.download = “converted-data.csv”; a.click(); }

function copyCSV() { navigator.clipboard.writeText(csvOutput); showMsg(“Copied to clipboard”, “green”); }