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Browser extension PHI guard

OpenMed PHI Guard is a Manifest V3 WebExtension under web/extension/. It detects PHI in editable fields and page text, then lets a user mask an active field before submitting it. Page text is visually masked in place. Detection runs in the extension's private background context through the typed openmed npm package; clinical text never leaves the browser. Chromium uses the Manifest V3 service worker, while Firefox uses the same bundle as a non-persistent background script.

Install for development

Build the unpacked extension with Node.js 20 or newer:

cd web/extension
npm ci
npm run build

Load web/extension/dist/ as an unpacked extension in Chromium-based browsers, or as a temporary add-on in Firefox. Store listing and submission are outside this package's scope.

The in-page panel provides:

  • a Mask PHI action for the active editable field;
  • a per-site enable/disable control stored in browser-local extension storage;
  • HIPAA Safe Harbor, clinical minimal-redaction, and strict no-leak profiles sourced from OpenMed's bundled policy JSON files.

The content script blocks form submission while any populated field is unscanned or stale, and when a current scan contains unmasked spans. Submit again only after the guard reports a current result. Review the masked result before sharing it because no automated detector guarantees complete recall.

Offline and privacy guarantees

The manifest declares only the storage permission and an empty host_permissions list. HTTP and HTTPS content-script matches allow the guard to inspect editable text, but no code path sends that text over the network. The background worker uses a compact local detector and the npm de-identification API, and its content security policy sets connect-src 'none'.

Only a site's enabled state and selected policy profile are persisted. Scan requests are schema-checked and capped at 1,000,000 characters and 4,000,000 UTF-8 bytes. Page text, raw identifiers, span output, and hashes are not stored. Password fields and non-text media are not inspected. See web/extension/PRIVACY.md for the user-facing privacy notice.

Test

Install the Playwright Chromium runtime once, then run the extension checks:

cd web/extension
npx playwright install chromium
npm test

The headless test loads the real unpacked extension on a synthetic page. It asserts that editable and text-node spans match the bundled detector output, masking produces the expected replacements, detection emits no HTTP(S) requests, per-site disable persists across reloads, and profile selection changes redaction behavior.

Limitations

This first version handles text only. It does not redact images, PDFs rendered to canvas, cross-origin frames, or browser-internal pages. It is a privacy safeguard, not a medical device, and it must not trigger clinical decisions.