Open
Import CSV for free. Pro adds structured-data and document sources through the Local Data Suite. Nothing is uploaded to Jason.
Solution / Large CSV
A large CSV viewer that keeps the file on your machine.
Open, search, sort, edit, calculate, and export oversized CSV files in a browser tab. Jason pages the working project through local storage; your spreadsheet content is not uploaded to Jason.
| A | B | C | D | E | F | |
|---|---|---|---|---|---|---|
| 1 | txn_id | posted_at | account | amount | fee | balance |
| 2 | 418002998 | 2026-07-02 | ACC-1037 | 19.73 | 0.37 | 814.47 |
| 3 | 418003005 | 2026-07-03 | ACC-1074 | 27.06 | 0.51 | 1117.06 |
| 4 | 418003012 | 2026-07-04 | ACC-1111 | 34.39 | 0.65 | 1419.65 |
| 5 | 418003019 | 2026-07-05 | ACC-1148 | 41.72 | 0.79 | 1722.24 |
| 6 | 418003026 | 2026-07-06 | ACC-1185 | 49.05 | 0.93 | 2024.83 |
| 7 | 418003033 | 2026-07-07 | ACC-1222 | 56.38 | 1.07 | 2327.42 |
| 8 | 418003040 | 2026-07-08 | ACC-1259 | 63.71 | 1.21 | 2630.01 |
| 9 | 418003047 | 2026-07-09 | ACC-1296 | 71.04 | 1.35 | 2932.60 |
| 10 | 418003054 | 2026-07-10 | ACC-1333 | 78.37 | 1.49 | 3235.19 |
| 11 | 418003061 | 2026-07-11 | ACC-1370 | 85.70 | 1.63 | 3537.78 |
| 12 | 418003068 | 2026-07-12 | ACC-1407 | 93.03 | 1.77 | 3840.37 |
| 13 | 418003075 | 2026-07-13 | ACC-1444 | 100.36 | 1.91 | 4142.96 |
| 14 | 418003082 | 2026-07-14 | ACC-1481 | 17.69 | 0.34 | 730.26 |
| 15 | 418003089 | 2026-07-15 | ACC-1518 | 25.02 | 0.48 | 1032.85 |
SUM 41,882,004.19ROWS 166,666,666LOCAL PROJECT — NOT UPLOADED
Largest measured file20.97 GB888 million cells
Measured first import3.9 min20.97 GB CSV
Measured cold open111 msmedian after import
Local project size0.795 GiB24.6× smaller than source
From file to working project01 02 03 04
Opening the file is only the first step.
Work
Search, sort, edit, calculate, and navigate the full dataset through a responsive canvas grid.
Return
Reopen the local project without paying the original import cost again.
Export
Write the result to CSV, or export the current view to Parquet with Pro.
Measured comparison
The difference is keeping the CSV workable.
The comparison below separates streaming a query across a file from opening the data as a spreadsheet project. Same machine, same pinned desktop Chrome, OPFS database, cross-origin isolation, spilling configured and confirmed accepted.
| Workload | DuckDB-WASM 1.33.1 | Jason |
|---|---|---|
| Run a query across the fileNever materialised — streaming scan | Completed — 14.05 GB in 76 s | Not the workload Jason optimises for |
| Open the file and keep it workableMaterialised — what a spreadsheet actually is | Failed — Out of memory at 1.76 GB, after 87 s | 11.78 GB held open, 1B cells |
Desktop Chrome. Edge, Firefox, and Chrome on Android are not measured. Hardware, storage speed, column shape, and data types can change the result. Use the benchmark as evidence, not as a guarantee for an untested machine.
Limits and data boundary
Know exactly what happens before choosing a file.
- Browser-local
- Spreadsheet content is imported, queried, edited, and exported on your device instead of being uploaded to Jason.
- Free source-file limit
- 1,000,000,000 bytes, exactly.
- Pro source-file limit
- No Jason-enforced limit; the device, browser, and available local storage still set practical limits.
- Measured scope
- The published large-file results were observed on Jason's development machine in desktop Chrome, not promised for every device.
Can a browser open a 20 GB CSV?
Jason measured one 20.97 GB CSV import in 3.9 minutes and a 111 ms median cold open after the local project existed. That is one documented machine and workload, not a promise that every 20 GB file opens everywhere.
Does Jason upload the CSV?
No. Spreadsheet rows stay in the browser-local data plane. Jason's separate commercial services handle account, payment, and signed licence state, not the source file.
Try the file before changing the workflow.
CSV starts free up to exactly 1,000,000,000 source bytes. If the measured method matters to your decision, inspect the benchmark before opening the file.