How do I convert a CSV file to XLSX format?

Send a POST request to https://api.convertfilefast.com/v2/convert/csv-to-xlsx with your CSV as a multipart/form-data upload using the file field. The API returns a binary XLSX file. See the cURL and Python examples above for ready-to-run code.

Is the output XLSX compatible with Microsoft Excel?

Yes. The output uses the Open XML SpreadsheetML format (ISO 29500), which opens natively in Microsoft Excel 2007 and later, Google Sheets, LibreOffice Calc, and Apple Numbers.

Does the API auto-detect CSV delimiters and encoding?

Yes. The API automatically detects common delimiters including comma, semicolon, tab, and pipe. It also handles UTF-8, ISO-8859-1, and Windows-1252 encodings without any extra configuration.

What are the file size and row limits for CSV to XLSX conversion?

Limits depend on your plan and are enforced per API key — the API reports the ceiling it currently accepts at https://api.convertfilefast.com/v1/info, and your own plan limit is shown in your dashboard.

Does the conversion preserve data types like dates, numbers, and strings?

Yes. The API applies automatic type coercion: ISO 8601 date strings are stored as Excel date values, numeric values become number cells, and all other values are stored as text. Each cell retains the correct Excel data type.

Can I integrate CSV-to-XLSX conversion in n8n, Zapier, or batch pipelines?

Yes. The API is a standard REST endpoint compatible with any HTTP client. It works out of the box with n8n HTTP Request nodes, Zapier webhooks, Make (Integromat), and Power Automate. See the n8n example tab above for a ready-to-import node configuration.

CSV to Excel, CSV to XLSX, Spreadsheet API

Convert CSV Files to Excel XLSX via API

Convert CSV files to Microsoft Excel XLSX spreadsheets via REST API. Upload your CSV file as multipart/form-data and receive a formatted Excel workbook in response. Perfect for report generation and data export pipelines.

Start Free View Documentation

# Convert CSV file to Excel XLSX
curl -X POST \
  https://api.convertfilefast.com/v2/convert/csv-to-xlsx \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -F "file=@data.csv" \
  --output output.xlsx

# HTTP 200 OK — Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet

import requests

response = requests.post(
    "https://api.convertfilefast.com/v2/convert/csv-to-xlsx",
    headers={"Authorization": "Bearer YOUR_API_KEY"},
    files={"file": open("data.csv", "rb")}
)

with open("output.xlsx", "wb") as f:
    f.write(response.content)

const formData = new FormData();
formData.append("file", fs.createReadStream("data.csv"));

const response = await fetch(
  "https://api.convertfilefast.com/v2/convert/csv-to-xlsx",
  {
    method: "POST",
    headers: { "Authorization": "Bearer YOUR_API_KEY" },
    body: formData,
  }
);

fs.writeFileSync("output.xlsx", Buffer.from(await response.arrayBuffer()));

// n8n HTTP Request Node
{
  "method": "POST",
  "url": "https://api.convertfilefast.com/v2/convert/csv-to-xlsx",
  "contentType": "multipart-form-data",
  "bodyParameters": {
    "parameters": [
      { "name": "file", "parameterType": "formBinaryData", "inputDataFieldName": "data" }
    ]
  },
  "options": { "response": { "responseFormat": "file" } }
}

Conversion completed in <2s

Advantages

Why use our API?

Complete and reliable solution for integration in any tech stack.

Excel-Ready Output

Receive a properly formatted XLSX file that opens directly in Microsoft Excel, Google Sheets, and LibreOffice Calc.

Simple Upload

Upload your CSV as multipart/form-data and receive the Excel XLSX binary in response. No configuration needed.

Column Formatting

CSV columns are mapped to Excel cells with automatic column width adjustment and header formatting.

Report Generation

Use in report generation pipelines to deliver data as Excel files to clients, stakeholders, and dashboards.

n8n & Automation

Convert CSV exports from databases or APIs to Excel in n8n workflows and send via email or save to Drive.

Zero Storage

CSV files are converted in memory and deleted immediately. Your data is never stored on our servers.

How it works

4 steps to run this conversion

1
Create an API key
Sign up at convertfilefast.com/signup and copy your cff_ API key from the dashboard. The free tier includes 10 conversions per month.
2
POST the CSV to the endpoint
Send a multipart/form-data POST to https://api.convertfilefast.com/v2/convert/csv-to-xlsx with header X-API-Key: cff_your_key (Authorization: Bearer also works), the CSV as a file field or a public url field.
3
Receive the XLSX spreadsheet
The response body is the resulting XLSX spreadsheet, streamed back with a Content-Disposition filename. Save it or pass it straight to the next step of your pipeline — nothing is stored on our side.
4
Or invoke it from an AI agent
Add the MCP server to Claude, Cursor or any MCP-compatible client using https://mcp.convertfilefast.com/mcp, then call convert_file({ target_format: 'xlsx', source_url: '...' }) as a single tool call — no HTTP client, no file handling.

For AI agents

Or call this from Claude, Cursor, or any MCP client

Convert File Fast ships a native Model Context Protocol server. Give this conversion to an AI agent as a single tool call — no HTTP client, no binary handling, per-user API keys.

Local install

npx -y convertfilefast-mcp

MCP tool call

convert_file({ target_format: "xlsx", source_url: "https://example.com/file.csv" })

Set up MCP Read llms-full.txt

Compared with

Convert File Fast vs alternatives

Product	Native MCP	Free tier	Price
Convert File Fast	Yes	10/month	$0.004/conv from $4
Smallpdf	No	2/day (unregistered)	$9/mo Pro
iLovePDF	No	Rate-limited	$7/mo Premium
Adobe Acrobat Online	No	Limited trials	$19.99/mo Acrobat Standard
CloudConvert	No	25 conv-min	From $0.01/min

Competitor pricing checked on 2026-07-16.

FAQ

Frequently Asked Questions

How do I convert a CSV file to XLSX format?: Send a POST request to https://api.convertfilefast.com/v2/convert/csv-to-xlsx with your CSV as a multipart/form-data upload using the file field. The API returns a binary XLSX file. See the cURL and Python examples above for ready-to-run code.
Is the output XLSX compatible with Microsoft Excel?: Yes. The output uses the Open XML SpreadsheetML format (ISO 29500), which opens natively in Microsoft Excel 2007 and later, Google Sheets, LibreOffice Calc, and Apple Numbers.
Does the API auto-detect CSV delimiters and encoding?: Yes. The API automatically detects common delimiters including comma, semicolon, tab, and pipe. It also handles UTF-8, ISO-8859-1, and Windows-1252 encodings without any extra configuration.
What are the file size and row limits for CSV to XLSX conversion?: Limits depend on your plan and are enforced per API key — the API reports the ceiling it currently accepts at https://api.convertfilefast.com/v1/info, and your own plan limit is shown in your dashboard.
Does the conversion preserve data types like dates, numbers, and strings?: Yes. The API applies automatic type coercion: ISO 8601 date strings are stored as Excel date values, numeric values become number cells, and all other values are stored as text. Each cell retains the correct Excel data type.
Can I integrate CSV-to-XLSX conversion in n8n, Zapier, or batch pipelines?: Yes. The API is a standard REST endpoint compatible with any HTTP client. It works out of the box with n8n HTTP Request nodes, Zapier webhooks, Make (Integromat), and Power Automate. See the n8n example tab above for a ready-to-import node configuration.

Start Converting CSV to Excel

Get your API key and convert CSV files to Excel XLSX in seconds. Free plan includes 10 conversions per month.

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