Data conversion tools that move information between the three most common formats — CSV, JSON, and Excel — plus XML and Markdown / HTML. Every tool auto-detects delimiter and record structure, flattens nested objects when needed, and preserves attributes or comments where formats support them. Drop in a file or paste the raw text; get a clean output ready for your next step. All conversions run client-side, so sensitive datasets never leave your browser.
For **CSV ↔ JSON** bidirectional conversion, use CSV ↔ JSON. For **JSON → CSV only** (with more flattening options), use JSON to CSV. To produce an actual **.xlsx** file, use CSV to Excel or JSON to Excel. To read an existing .xlsx, use Excel to CSV (multi-sheet-aware). For **XML** data, XML to JSON preserves the tree structure; XML to CSV flattens into rows and columns. For **documentation** workflows, Markdown to HTML and HTML to Markdown round-trip cleanly.
What's the largest dataset I can convert?
Tens of thousands of rows work comfortably. For multi-hundred-thousand-row files, the main thread may block briefly during parsing — modern browsers handle it, older devices may not.
Do the Excel tools support multiple sheets?
Excel to CSV shows every sheet as a picker tab so you can convert each separately. CSV to Excel and JSON to Excel produce single-sheet output (multi-sheet input → output is a Phase 9 stretch).
How are nested objects handled in JSON → CSV?
Optionally flattened: nested object keys become dot-notated column headers ("user.name"), nested array elements become bracket-indexed ("tags[0]"). Toggle flattening off to keep nested structures as JSON strings inside a single cell.
Is Markdown handled with sanitisation?
Yes — Markdown to HTML uses marked + DOMPurify so pasted content is safe to drop into a live page. Turn sanitise off only if you trust the input.
Are any of these tools uploading my files?
No. Every tool in this category runs entirely in your browser. Files you drop in are processed locally, never sent to a server, and discarded when you leave the page.