Your CSV never leaves your machine.
Flow Lens is a single HTML file that runs entirely inside your web browser. It has no server, no backend, and no data transmission. The CSV file you load into it never leaves your machine under any circumstances.
Flow Lens is a local browser tool. It reads a CSV from your file system into browser memory, renders charts, and discards the data when you close the tab. No data is sent anywhere, no accounts are required, and nothing is installed.
Data handling
| Is the CSV uploaded to any server? | No — read by the browser's File API into memory only. |
| Is any data transmitted over the internet? | No — CSV data never leaves the device. |
| Is any data written to disk or browser storage? | No — no localStorage, cookies, or IndexedDB writes. |
| Is data retained after closing the tab? | No — all data is discarded on tab close. |
| Does the tool collect analytics or telemetry? | No — no analytics, no usage tracking, no error reporting. |
| Is a login or account required? | No. |
| Does it make any network requests? | No — fully self-contained, works offline immediately. |
| Can it be used offline? | Yes — always, with no setup required. |
Network activity
Flow Lens makes zero automatic network requests. All JavaScript libraries are bundled directly inside the HTML file. Opening the tool does not contact any external server under any circumstances. No CDN, no external dependencies, no internet connection required — ever.
Libraries bundled inside the file
- Chart.js 4.4.0 — renders all charts.
- PapaParse 5.4.1 — parses your CSV in the browser.
- date-fns 3.6.0 — date arithmetic for cycle-time calculations.
The tool is a single self-contained file. Versions above are embedded at fixed pins.
Verify it for yourself
The whole tool is open source. Read the HTML, run it through a static analyser, open it offline — anything you'd do with a normal file.