How to Convert Base64 to Excel — Python, JavaScript & No-Code

HTTP/1.1 200 OK
Content-Type: application/json
{
"report_name": "Q3_Sales_Summary",
"generated_at": "2025-06-01T09:00:00Z",
"format": "xlsx",
"file": "UEsDBBQABgAIAAAAIQBi7p1oXgEAAJAEAAATAAgCW0..."
}

import base64
Your Base64 string (from API response, DB, etc.)
base64_string = "UEsDBBQABgAIAAAAIQBi7p1oXgEAAJAEAAATAAgCW0..."
Decode to bytes
file_bytes = base64.b64decode(base64_string)
Write to disk as .xlsx
with open("output.xlsx", "wb") as f:
f.write(file_bytes)
print("Excel file saved successfully")}                             </pre>                         </div>                         <p className="text-gray-700 leading-relaxed mb-4">                             If the Base64 string came from a JSON API response, parse the JSON first:                         </p>                         <div className="bg-gray-900 rounded-xl p-6 my-6">                             <div className="text-gray-400 text-xs font-mono mb-3">python — from API JSON response</div>                             <pre className="text-green-400 font-mono text-sm overflow-x-auto"> {import requests
import base64
response = requests.get("https://your-api.example.com/report")
data = response.json()
Extract Base64 string from the response field
base64_string = data["file"]
Handle data URI prefix if present
if "base64," in base64_string:
base64_string = base64_string.split("base64,")[1]
file_bytes = base64.b64decode(base64_string)
filename = data.get("report_name", "output") + ".xlsx"
with open(filename, "wb") as f:
f.write(file_bytes)
print(f"Downloaded: {filename}")

const fs = require("fs");
// Your Base64 string
const base64String = "UEsDBBQABgAIAAAAIQBi7p1oXgEAAJAEAAATAAgCW0...";
// Strip data URI prefix if present
const clean = base64String.includes("base64,")
? base64String.split("base64,")[1]
: base64String;
// Decode and write
const buffer = Buffer.from(clean, "base64");
fs.writeFileSync("output.xlsx", buffer);
console.log("Saved output.xlsx —", buffer.length, "bytes");}                             </pre>                         </div>                         <p className="text-gray-700 leading-relaxed mb-4">                             For async workflows or when working inside an Express route:                         </p>                         <div className="bg-gray-900 rounded-xl p-6 my-6">                             <div className="text-gray-400 text-xs font-mono mb-3">node.js — express route: stream xlsx to client</div>                             <pre className="text-green-400 font-mono text-sm overflow-x-auto"> {app.get("/download-report", async (req, res) => {
const apiData = await fetchReportFromExternalAPI();
const base64 = apiData.file;
const buffer = Buffer.from(
base64.includes("base64,") ? base64.split("base64,")[1] : base64,
"base64"
);
res.setHeader("Content-Type",
"application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
res.setHeader("Content-Disposition",
'attachment; filename="report.xlsx"');
res.send(buffer);
});

function downloadBase64AsExcel(base64String, fileName = "output") {
// Strip data URI prefix if present
const clean = base64String.includes("base64,")
? base64String.split("base64,")[1]
: base64String;
// Decode Base64 to binary string
const binaryStr = atob(clean);
// Convert to Uint8Array
const bytes = new Uint8Array(binaryStr.length);
for (let i = 0; i < binaryStr.length; i++) {
bytes[i] = binaryStr.charCodeAt(i);
}
// Create Blob with correct MIME type
const blob = new Blob([bytes], {
type: "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
});
// Trigger download
const url = URL.createObjectURL(blob);
const a = document.createElement("a");
a.href = url;
a.download = fileName + ".xlsx";
document.body.appendChild(a);
a.click();
document.body.removeChild(a);
URL.revokeObjectURL(url);
}
// Usage
downloadBase64AsExcel(apiResponse.file, apiResponse.report_name);

data:application/vnd.openxmlformats-officedocument.spreadsheetml.sheet;base64,UEsDBBQABgAIAAAA...