LocalcraftTHE EVERYDAY TOOLKIT
LOCAL FILES. CLEAR RESULTS.

How local processing works

Every file tool on Localcraft runs inside your browser tab. This page explains the mechanics — and how to prove it yourself with airplane mode and a network tab.

The short version

When you use a Localcraft file tool, your file is read by JavaScript running in this browser tab, processed in memory, and handed back to you as a download. At no point is the file sent to a server — there is no upload endpoint for it to go to. This page explains the mechanics in enough detail to check them yourself.

Step by step: what happens to a file

  1. You pick a file. The browser’s file picker gives the page a File handle. The tool reads it with the standard File API (arrayBuffer() / createImageBitmap) into the tab’s memory. Nothing has left the device.
  2. The tool works in the tab. PDF tools use pdf-lib and unpdf, image tools use the Canvas API and WebCodecs where available, media tools run FFmpeg compiled to WebAssembly, the background remover runs a segmentation model through Transformers.js. All of it executes on your CPU/GPU, in this tab.
  3. You download the result. Output is assembled as a Blob in memory and saved through an object URL — the same mechanism the page itself uses, with no server round-trip.
  4. Closing the tab erases everything. Inputs and results live only in tab memory. Localcraft keeps no server-side copy, because none was ever made.

What the server actually does

The web server’s only job is delivering the static page and its code (HTML, CSS, JavaScript, WebAssembly engines and AI models) when you open or first run a tool. Some engines are large — the media engine is about 32 MB and the background-removal model about 473 MB — and your browser caches them after the first download. Those downloads are programs, flowing to your device; your files never flow the other way. A page-view counter records that a page was opened (no file names, sizes or contents), and the optional AI tools are the single exception described below.

The one exception: AI tools with your own key

The tools labelled “AI” (chat, summarizer, image analyzer and similar) call the AI provider you choose, with your API key, over HTTPS. What you type or upload in those tools goes to that provider — never to Localcraft, and never anywhere else. The background remover is not part of this exception: its model runs locally like every other file tool. If you never open an AI tool, nothing you do on this site leaves your device.

Prove it yourself

  1. Airplane-mode test. Open any file tool (for example Compress PDF) and let it load. Switch your device to airplane mode — or disconnect Wi-Fi. Now choose a file, run the tool and download the result. It works offline, because everything it needs is already in the tab. (Media tools and the background remover need their one-time engine/model download first; run them once online, then repeat the test.)
  2. Network-tab test. Open your browser’s developer tools (F12), go to the Network tab, and process a file. You will see no upload of your file — processing produces no request carrying it. Compare that with any cloud converter, where the first thing that happens is a large POST with your file inside.
  3. Read the limits. Server-side converters limit file size because storage and bandwidth cost them money. Localcraft’s limits are published per tool and exist only to keep your tab from running out of memory.

Questions

See the privacy notes for the legal version of this page, or email [email protected] if you find a case that behaves differently from what is described here — that would be a bug, and it would be fixed.