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Browser security

What WASM security actually means.

A grounded look at what the browser sandbox helps with, what it does not magically solve, and how local PDF workflows should be verified.

8 min readBrowser sandboxLocal processing

The browser is the boundary

WebAssembly runs inside the same browser security model as JavaScript. It can be fast, but it does not receive special operating-system privileges.

That matters for document tools because selected files are exposed through browser file objects, not through open-ended access to your drive.

Security boundaries

  • Memory isolation: WASM works inside its own linear memory.
  • User-selected files only: A page cannot browse your filesystem without your explicit file-picker action.
  • Network visibility: Requests still pass through browser networking and can be inspected in developer tools.
  • No system APIs: WASM cannot start processes or open raw sockets like native apps.

Verification beats vibes

Open the Network tab, load a document, run the workflow, and confirm whether document bytes are sent to a remote endpoint. Good privacy UX should make that route understandable.

What WASM does not solve

WASM does not automatically make bad code safe. A local tool still needs careful dependency choices, clear route labels, safe file handling, and no hidden upload path.

How to verify local processing

  1. Load the page and open browser developer tools.
  2. Switch to the Network panel.
  3. Select a test PDF and run the workflow.
  4. Confirm no document upload request appears during processing.
  5. Disconnect after load and test whether the supported workflow still runs.