Claims with a measuring tape.
These are observed results on a Jason development machine in Chrome, not promises for every device.
Hardware, browser version, storage speed, column shape, and data type distribution all affect results.
Recorded runs
| Run | Source | Cells | First import | Cold open | Notable result |
|---|---|---|---|---|---|
| Large CSV / A | 20.97 GB | 888M | 3.9 min | 111 ms median | 0.795 GiB project |
| Billion-cell / B | 11.78 GB | 1B | 174.6 s | 93 ms median | 0 dropped frames |
Measured against DuckDB-WASM 1.33.1
Every local browser tool in this category is DuckDB-WASM underneath, so formats are not the difference — they all read the same ones. The difference is what happens when the data has to stay open. 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 |
The obvious objection was tested rather than assumed. The probe told DuckDB to spill to disk and recorded that every setting was accepted; it still ran out of memory, and it took 87 seconds to do it on a file it scans in 9. Desktop Chrome. Edge, Firefox, and Chrome on Android are not measured.
How to read these numbers
First import includes parsing the CSV and writing Jason's local project. Cold open measures reopening that already-built project. These are deliberately reported separately: one is a conversion cost, the other is the recurring working experience.
What is not claimed
Jason does not claim that every 20 GB file opens on every machine, that all datasets compress by the same ratio, or that all browsers reproduce these timings. The Free plan is also capped at exactly 1,000,000,000 source bytes.
Measure it with your own file.
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