1 · A database engine loads into the tab

DuckDB — the same analytical engine data teams run on servers — is compiled to and shipped inside this page. It runs in a Web Worker, so a long scan never freezes the interface. It is served from this site, not a CDN, so no third party learns that you opened it.
2 · Your file is registered, not uploaded

Gridwell hands the engine a reference to the file you picked. DuckDB then reads it in ranges, directly off your disk, as each query needs it — which is why a 2 GB file opens as quickly as a 2 MB one and never has to fit in memory.
3 · The dialect and types are sniffed

Delimiter, quoting, header row and the type of every column are detected by scanning the file. Gridwell reads all of it rather than a sample, which is what stops a column being guessed as a whole number and then failing eight hundred thousand rows later.
4 · You filter, in clicks or in SQL

The builder writes real into the editor as you click, so you can start with buttons and end up editing the query directly. Only read-only statements run — nothing can modify your file.
5 · Results come back column-at-a-time

Results arrive in a format the grid can read . Only the rows on screen are drawn, so scrolling stays smooth at any size.
6 · You export what you actually needed

Write the filtered result back out as CSV, JSON or . The export is generated in the tab and handed straight to your browser's downloads.

Protected

The contents of your file. It is read by the WebAssembly engine inside this tab. There is no upload endpoint in this application — not a slow one, not an optional one. None.
Your column names, row counts and schema. Never transmitted, never logged, never used for analytics.
Every query you write. The SQL runs locally and is not recorded anywhere outside this tab.
Your exports. Generated in memory and handed to your browser's download machinery directly.
Nothing survives the tab. The database is in-memory. Close the tab and every trace of your data is gone. Only interface preferences are stored locally.

Not protected

That you visited. An anonymous page view is counted (see below), and your network operator can see you loaded this domain — never what you opened in it.
Anything on your own machine. This is a local tool, not a vault. Exported files land in your Downloads folder unencrypted, and anyone with access to your device or browser profile can see them.
Shoulder surfing and screen sharing. Your data is on screen. If you are on a call, it is on their screen too.
Browser extensions. An extension with permission to read pages can read this one, exactly as it can read any other. Consider a private window for genuinely sensitive files.

Trust surface

This site's bundle, served over TLS by GitHub Pages — including the DuckDB WebAssembly binary, which ships inside it rather than being fetched from a CDN at runtime. The source is public and linked in About.
Your browser and its WebAssembly sandbox.
A Cloudflare Web Analytics beacon records anonymous page views — no cookies, no fingerprinting, no cross-site tracking; your files and data are never sent to it.
Feedback you choose to send (and an email address, only if you supply one) is sent to feedback.benrichardson.dev. Nothing is sent unless you open the feedback form and press Send; your files and data never are.

You do not have to take any of this on faith. Open your browser's developer tools, switch to the Network tab, and load a file — you will see no request carrying your data, because there is none.

Your CSV is too big for Excel.

Starting the query engine…

Query

Results

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