Open
Import CSV for free. Pro adds structured-data and document sources through the Local Data Suite. Nothing is uploaded to Jason.
Product / 01
Big files become working files.
Jason is a browser spreadsheet engine for source files that exceed the practical limits of ordinary spreadsheet apps. CSV starts free; Pro adds the Local Data Suite for structured data and documents.
| 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
From source file to reusable project
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.
Source formats
Open the shape the work already has.
Jason preserves typed records where the source has them and gives documents an explicit row model instead of pretending prose is a spreadsheet table.
- Delimited text / Free
- CSV, TSV, and TXT, including gzip or single-file ZIP containers.
- Structured data / Pro / Local Data Suite
- JSON Lines, XLSX, SQLite, Parquet, Arrow IPC / Feather v2, dBase (.dbf), and Avro.
- Documents and collections / Pro / Local Data Suite
- Word (.docx) outlines or tables, PowerPoint (.pptx) slides, and EPUB content blocks. Merge up to 500 CSV tables or Word outlines; Word rows retain their source filename.
Architecture / local-first
The product is split where trust should be split.
The spreadsheet engine reads and transforms data in the browser. Commercial services handle only account, payment, and signed licence state. File rows do not need to cross that boundary.
- Import
- Browser-local processing into a persistent local project.
- Grid
- Canvas rendering keeps the visible surface small and responsive.
- Calculation
- Computed locally; advanced calculated columns are a Pro capability.
- Licence
- Short-lived, signed receipt that is verified by the product.
Do not shrink the question to fit the tool.
Open an oversized CSV for free. Pro removes Jason's limits and adds structured-data, document, and multi-file Local Data Suite tools.