Data tools
13 tools that run in your browser. Nothing to install, nothing uploaded.
Open a CSV or a spreadsheet without a spreadsheet program, and convert between them, with the file parsed inside your browser rather than uploaded. Business data is the category people paste into unfamiliar web tools with the least thought and the most exposure — a customer export or a payroll sheet is a disclosure incident, not an inconvenience. These tools also lead with what a conversion costs rather than burying it: turning an XLSX into CSV drops formulas to their last computed values, loses every bit of formatting, and splits each sheet into its own file, and the viewer flags the ragged rows that will break whatever you feed them into next.
- CSV DeduplicatorRemove exact duplicate rows and flag the conflicting ones.
- CSV SplitterSplit a long CSV into parts that each keep the header.
- CSV to HTML TableConvert a CSV into accessible, escaped HTML table markup.
- CSV to Markdown TableTurn a CSV into a Markdown table, with pipes escaped properly.
- CSV to XLSXTurn a CSV into a workbook without letting the spreadsheet mangle your data.
- CSV ViewerView a CSV as a table — and find the rows that do not line up.
- Excel Sheet MergerCombine sheets by column name, so nothing lands in the wrong field.
- HTML Table to CSVPull a table out of HTML and get clean CSV back.
- JSON to XLSXTurn JSON into a workbook, with nested objects flattened rather than stringified.
- Markdown Table GeneratorPaste spreadsheet cells and get a formatted Markdown table.
- XLSX to CSVConvert a spreadsheet to CSV, one file per sheet, with what gets lost stated first.
- XLSX to JSONConvert a spreadsheet to JSON without turning dates into serial numbers.
- XLSX ViewerOpen a spreadsheet without a spreadsheet program — and without uploading it.
Spreadsheets are the files people upload most carelessly
A CSV or XLSX in a work context is usually a customer list, an export from a CRM, a payroll sheet or a set of financial records — and it is routinely pasted into the first free converter a search returns. That is a disclosure of somebody else’s personal data to a third party, and in most regulatory regimes it is exactly the kind of transfer that has to be documented and justified. These tools parse the file inside your browser, so the data never leaves the machine it was already on. The check is easy: open the network panel, load a file, and watch for a request that never comes.
What converting a spreadsheet to CSV actually costs
CSV is a plain text format with no concept of most of what a spreadsheet contains, so a conversion is a deliberate discard rather than a translation. Formulas are replaced by their last computed values. Formatting, colours, column widths, merged cells, charts and images are gone entirely. Multiple sheets cannot exist in one CSV, so each becomes its own file. Dates are the subtle one — they are stored as serial numbers and rendered by a format that CSV cannot carry, so the output depends on how they were displayed. The converter states all of this before you run it rather than after.
The rows that break whatever you feed them into
Most CSV failures downstream come from a handful of structural problems that are invisible when you scroll through a file. Rows with a different number of fields to the header, usually caused by an unescaped comma or a stray quote. Line breaks inside quoted values, which split one record into two for any parser that reads line by line. Mixed encodings, where a file that is mostly ASCII carries a few UTF-8 bytes an importer misreads. The viewer flags ragged rows explicitly, because finding them here takes a moment and finding them after a failed import into a production system takes an afternoon.
Frequently asked questions
Is my spreadsheet uploaded?
No — it is parsed in your browser and never transmitted. This is worth being deliberate about, because the files in this category are typically customer exports, payroll sheets or financial records, and putting one through a random online converter is a disclosure of other people’s personal data to a third party that most regulatory regimes expect you to be able to justify. Open the network panel and load a file if you want to confirm it.
What do I lose converting XLSX to CSV?
More than people expect, because CSV is plain text with no concept of most of a spreadsheet. Formulas become their last computed values. All formatting, colours, column widths, merged cells, charts and images are gone. Each sheet has to become its own file, since CSV holds one table. Dates are the subtle one — they are stored as serial numbers and displayed by a format CSV cannot carry, so the output depends on how they were shown.
Why does the viewer flag some of my rows?
Because they have a different number of fields to the header, which is the structural fault that breaks imports downstream. It is almost always an unescaped comma inside a value, a stray or unbalanced quote, or a line break inside a quoted field that splits one record in two for any parser reading line by line. Finding these here takes a moment; finding them after a failed import into a production system takes considerably longer.
How large a file can it open?
Large ones, bounded by your own machine’s memory rather than by an upload limit, since nothing is transferred. Files in the tens of megabytes generally open without trouble. Very large spreadsheets can make the tab briefly unresponsive while parsing, which is the trade-off for doing the work locally — and a better trade than the alternative for anything containing real data.