neoprint.detectIncognito()

Detect private / incognito browsing mode.

Signature

function detectIncognito(): Promise<{
  isIncognito: boolean
  signals: string[]
}>

Returns

• isIncognito — true if any strong signal detected
• signals — which heuristics triggered

Detection by Browser

Browser	Method	Signal
Chrome	Storage quota drops from ~10GB to ~4GB	low_storage_quota
Chrome	navigator.languages trimmed to 1 entry	languages_trimmed
Safari	Storage quota drops from ~82GB to ~1GB	low_storage_quota
Safari	OPFS (getDirectory) throws error	opfs_blocked
Safari	speechSynthesis.getVoices() returns 0 voices	no_speech_voices
Firefox	navigator.serviceWorker is undefined	firefox_no_serviceworker

Example

const result = await neoprint.detectIncognito()

if (result.isIncognito) {
  console.log('Private browsing:', result.signals)
}

Limitations

Safari has been the most aggressive at patching detection methods. The current approach is based on real-world measurements (2026) and may need recalibration as browsers evolve. Chrome on localhost reports lower quota than on real domains.