Read the guideOpen Jason

The spreadsheet for files that do not fit.

Open Jason free Inspect benchmarks
  • For CSVs measured in gigabytes
  • For rows a spreadsheet app refuses
  • Runs entirely in your browser
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

Open the file your spreadsheet refuses

Before

“File too large to open.”

After

A local project you can reopen in milliseconds.

Importledger-2026.csv
Read source20.97 GB
Parse rows148,003,112
Infer types6 columns
Write local project0.795 GiB
ELAPSED 2:24NETWORK 0 BSOURCE STAYS ON DISK

A 20.97 GB CSV became a working project in 3.9 minutes on the measured run.

CapabilitiesStreaming CSV importLocal project formatType inferenceImport limits

Move through a billion cells without waiting

A one-billion-cell project scrolled with zero dropped frames and reopened in 93 ms median.

CapabilitiesCanvas grid rendererSearch and sortFormulas and calculated columnsMeasured runs
reconciliation-2026.jason1,000,000,000 cellsD4:D999999999=SUM(D:D)
ABCDEF
1txn_idposted_ataccountamountfeebalance
24180029982026-07-02ACC-103719.730.37814.47
34180030052026-07-03ACC-107427.060.511117.06
44180030122026-07-04ACC-111134.390.651419.65
54180030192026-07-05ACC-114841.720.791722.24
64180030262026-07-06ACC-118549.050.932024.83
74180030332026-07-07ACC-122256.381.072327.42
84180030402026-07-08ACC-125963.711.212630.01
94180030472026-07-09ACC-129671.041.352932.60
104180030542026-07-10ACC-133378.371.493235.19
114180030612026-07-11ACC-137085.701.633537.78
124180030682026-07-12ACC-140793.031.773840.37
134180030752026-07-13ACC-1444100.361.914142.96
144180030822026-07-14ACC-148117.690.34730.26
154180030892026-07-15ACC-151825.020.481032.85
SUM 41,882,004.19ROWS 166,666,666LOCAL PROJECT — NOT UPLOADED
Rendered per frame

~2,400

visible cells — the other billion stay in the local project until you scroll to them.

Keep every row on your own machine

Bytes uploaded

0

Import, edit, calculate and export all happen inside the browser tab.

Data boundary0 rows leave the device
Your machine
ImportSearchSortEditCalculateExport
Jason servers
Account emailSubscription stateSigned licence receipt
DATA PLANE LOCALCOMMERCIAL PLANE MINIMAL

Spreadsheet content never reaches a Jason server — there is nothing to upload and nothing to breach.

CapabilitiesData boundaryLicense modelOffline behaviourExport to CSV

One file, one working loop

01

Open

Import a CSV into a browser-local project without uploading the file to Jason.

02

Work

Search, sort, edit, calculate, and navigate the full dataset through a responsive canvas grid.

03

Return

Reopen the local project without paying the original import cost again.

04

Export

Write the result back to CSV when the work is done.

Recently shipped

Benchmark

Billion-cell scroll run

11.78 GB source imported in 174.6 s, then scrolled with zero dropped frames.

Engine

Exact accumulation for money columns

Sum and average over currency columns no longer drift on long columns.

Performance

Cold open under 120 ms

Reopening an imported project no longer repeats the import cost.

Security

Signed license receipts

Pro capability is granted only against a subject-bound ES256 receipt.

Stop shrinking the question to fit the tool.

Open a CSV that your spreadsheet app refuses. Free covers files up to 1 GB and three local projects.

Open Jason free Inspect the benchmarks