Huge CSV / Viewer
21 GB tested

Your data,
ready to explore.

A fast, private workspace for opening the CSV files spreadsheets cannot — parsed in parallel by a streaming WebAssembly parser, directly in your browser. Nothing is uploaded. Need a test file? Generate one up to 20 GB.

Drop your file anywhere

CSV, TSV, semicolon, or tab-delimited

Preview

No file selected

Export

Split CSV

#Column AColumn BColumn CColumn D
Your table will appear here Open a file to begin exploring its rows and columns.

CSV Viewer, Reader & Splitter

csv generator · how the WASM parser works · what to do with a huge CSV

Fast CSV Viewer is a free online CSV viewer and CSV splitter built for large files. Drop in a .csv, .tsv or delimited file and it is parsed, laid out as a table and ready to sort, filter, search, export and split instantly — directly in your browser. The CSV splitter turns one big file into many smaller ones, each keeping the header row.

Your file never leaves your computer. There are no servers — no upload and no server-side parsing — so even huge, sensitive CSV files stay completely private and secure: your data never leaves your browser. A streaming WebAssembly RFC 4180 parser and virtual scrolling keep things fast on big and multi-gigabyte CSV files — tested in the browser with a 21 GB file of 100 million rows. Once the page has loaded it even works offline, with no network connection at all.

What you can do

  • Open large CSV files — view huge and big CSV files that crash spreadsheets and editors.
  • Split a big CSV into many files — the built-in CSV splitter writes N parts of roughly equal size, each keeping the header row.
  • Export & convert — save the rows as JSON, YAML or a SQLite .sql dump, streamed to disk.
  • Sort columns — click a header to sort ascending, descending or off, numeric-aware.
  • Filter rows — keep rows matching a substring or regex, per column or across all columns.
  • Resize & auto-fit columns — drag a column edge, or fit every column to its widest cell instantly.
  • Auto-detect the delimiter — comma, semicolon and tab (TSV), or force one from the toolbar.
  • Handle real-world CSV — quoted fields, doubled quotes, embedded newlines, CRLF/LF and BOM.
  • View CSV online for free — no install, no signup, works in any modern browser.
  • Secure & offline — no servers, your data never leaves your browser, and it works with no network once loaded.

Frequently asked questions

How do I open a large CSV file?
Drag and drop your .csv file onto this page, or click Open CSV to browse for it. Fast CSV Viewer streams the file inside your browser and paints the first rows before parsing finishes, so even large CSV files open quickly.
What is the largest CSV file I can open?
There is no fixed limit. The viewer streams CSV in small blocks across multiple web workers and uses virtual scrolling, so it has been tested in the browser with a 21 GB file of 100 million rows. Practical limits depend on your device's available memory and browser.
Is my CSV file uploaded to a server?
No. Your file is opened and parsed entirely on your own device. There is no upload and no server-side processing, so private and sensitive CSV files never leave your browser.
Is it secure, and does it work offline?
Yes to both. Fast CSV Viewer has no servers and no backend: your file is opened and parsed entirely on your own device by a WebAssembly parser running in your browser, so your data never leaves your browser. And once the page has loaded, a service worker caches the app and the parser, so you can open, read, sort and filter CSV files completely offline, with no network connection at all.
Can I sort and filter CSV columns?
Yes. Click any column header to sort it ascending, descending or off (sorting is numeric-aware). Use the filter box to keep only rows that match a substring or a regular expression, scoped to one column or all columns. Both run as a streaming scan over the whole file, locally in your browser.
Can I split a large CSV into multiple files?
Yes. Open the Export & split menu in the toolbar, choose how many files you want, and click Split. The CSV splitter streams the file and writes that many parts of roughly equal size, each one beginning with the original header row, splitting only on whole-row boundaries so a quoted field with an embedded newline is never cut. In a Chromium browser you pick an output folder and the parts are written straight to disk, so it works on multi-gigabyte files; other browsers download each part. Everything runs locally — your data never leaves your browser.
Can I export or convert the CSV to JSON, YAML or SQL?
Yes. The Export & split menu can convert the open CSV to a JSON array of records, a YAML document, or a SQLite-compatible .sql dump (CREATE TABLE plus batched INSERTs, imported with sqlite3 out.db < dump.sql). The conversion is streamed block by block and written straight to disk, so it works on huge files, and it only runs when you pick a format. See what to do with a huge CSV for a step-by-step SQLite import and example queries.
Does it handle quoted fields, embedded newlines and different delimiters?
Yes. The parser follows RFC 4180: it handles quoted fields, doubled-quote escapes, embedded commas and newlines inside quotes, and CRLF or LF line endings — even when a field is split across the 256 KB streaming block boundary. The delimiter is auto-detected, and you can force comma, semicolon or tab.
Can I view CSV online for free?
Yes. Fast CSV Viewer is completely free, with no signup and no installation. It runs in any modern browser, so you can view CSV online from any computer.
Can I resize or auto-fit columns?
Yes. Drag a column's right edge to resize it, or click Fit columns to size every column to its widest cell. The parser measures the maximum width of each column while streaming, so auto-fit is instant even on huge files, and your column widths are remembered for files with the same header.
Does it support TSV and semicolon-separated files?
Yes. The viewer auto-detects the delimiter and supports comma, semicolon and tab-separated (TSV) files. You can also override the delimiter manually from the toolbar.
How do I create a huge CSV test file?
Use the CSV generator page to stream a CSV file of any size up to 20 GB straight to your disk via the File System Access API. Pick the delimiter, line ending, column count, language and quoting hazards. The data never touches a server and there is no temporary copy in memory — the file is written incrementally as it is generated. Use it to benchmark CSV parsers or to stress-test Fast CSV Viewer on huge inputs.
How does the WebAssembly CSV parser work?
The whole CSV parse runs in your browser in a WebAssembly module compiled from C — a streaming RFC 4180 state machine that reads the file in 256 KB blocks across web workers. Because the workers parse blocks in parallel, a block doesn't know whether it begins inside a quoted field, so the parser runs two hypotheses at once and a validator stitches the surviving one across boundaries. On a 100 MB file it parses at about 309 MB/s, roughly 2.3× faster than the equivalent JavaScript, from a module under 4 KB. There's a full write-up — the C source, the exact clang compile flags, and the benchmark — in how the WASM parser works.
I have a huge JSON file — how do I view it?
Use Fast JSON Viewer — the fastest JSON viewer in the world. Like Fast CSV Viewer, it runs entirely in your browser with no upload: it streams multi-gigabyte JSON in small blocks across web workers and starts rendering before parsing finishes, and it has been tested on files up to 20 GB. It pretty-prints and syntax-highlights JSON, validates as it parses with precise error locations, lets you collapse and expand structure instantly, and can convert JSON to YAML or export an array of records to CSV — all locally with virtual scrolling. Nothing is uploaded and there is no server-side parsing, so private data never leaves your machine.
Drop to open
IDLE