Convert CSV to XLSX online

Convert CSV to XLSX online in batches. Files stay in your browser and are never uploaded or stored on a server.

Only ad you'll see

From

Your files stay on this device and are never uploaded.

Drop files here to convert them

Up to 20 files · 50 MB each · 100 MB per batch

Choose CSV files and convert them to XLSX together in one private browser session.

How to convert CSV to XLSX

Select one or more CSV files, start the batch, then download each XLSX result or all completed files together.

This conversion reads each CSV table and writes its rows and columns to a new XLSX spreadsheet file.

Process up to 20 files per batch, with 50 MB per file and 100 MB in total.

The conversion runs locally in your browser. NDNCI never receives, stores, or sends your files to a third party.

Audio Converter

Convert MP3 and WAV audio, or extract MP3 audio from MP4, in private browser-only batches with no uploads.

Base32 Encoder/Decoder

Encode UTF-8 text to Base32 or decode Base32 values locally.

Base64 Encoder/Decoder

Encode or decode Base64 strings.

Image Converter

Convert PNG, JPEG, and WebP images in private browser-only batches with no uploads.

Markdown/HTML Converter

Convert between Markdown and HTML in both directions.

URL Encoder/Decoder

Encode or decode URLs quickly.

Video Converter

Convert MP4, MOV, and WebM videos in private browser-only batches with no uploads.

Image Upscaler

Upscale images 2× locally, with optional AI acceleration and browser fallbacks.

Video Upscaler

Upscale videos 2× locally, using AI and WebGPU when available with a browser fallback.

3D Model Viewer

Open 3D models locally, inspect geometry, materials and textures, then download the original files.