CSV to XLSX
Convert CSV files to Excel spreadsheets. Paste or upload.
Also try: XLSX to CSV · JSON ↔ CSV
100% client-side. Your data never leaves your browser.
Using AI? Optimize your prompts first.
Better prompts = better output = fewer revisions.
Try the Prompt Optimizer — Free →You might also like
XLSX to CSV Converter
Convert Excel spreadsheets to CSV instantly. Multi-sheet support, select any tab. Free, 100% client-side.
JSON to CSV Converter
Convert between JSON and CSV instantly. Bidirectional conversion, paste and go. Free, runs in your browser.
PDF to Markdown Converter
Convert PDF files to clean markdown. Save up to 95% on tokens when pasting into ChatGPT, Claude, or Gemini. Free, 100% client-side, no upload.
AI Prompt Optimizer
Paste any AI prompt and get an optimized version using the ICCSSE framework. Works for ChatGPT, Claude, and Gemini. Free, no signup, runs in your browser.
100% client-side where applicable — your files and inputs stay in your browser. Nothing is uploaded to HundredTabs servers for these tools.