Local · Web Crypto

Password strength checker

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There is no upload endpoint — your files are processed in this browser tab. Open your network tab and check. See how it stays private.

How to check password strength

  1. Type a candidate. Enter the password you're considering.
  2. Read the score. See the 0–4 strength score with an estimated time to crack.
  3. Fix the warnings. Address the flagged patterns — common words, sequences, repeats.
  4. Iterate. Adjust until the estimate reaches a comfortable margin.

Most strength meters lie: they reward a capital letter and a digit even when the result is trivially guessable. zxcvbn scores differently, estimating how many guesses an attacker would actually need given the patterns humans reuse, then converting that to a crack-time you can reason about.

The warnings are the useful part — "this is a top-1000 password," "predictable substitutions," "a keyboard pattern" — because they tell you what to change instead of just showing a red bar.

Once you've settled on a strong secret, store it and its siblings in a Password Desk KeePass vault, and use the Password hasher if you need a hash for a dev workflow.

Frequently asked questions

How is password strength measured?

This uses zxcvbn, which models how attackers actually guess — dictionaries, common substitutions, keyboard walks — rather than naive length rules, so the estimate reflects real-world cracking.

What makes a strong password?

Length and unpredictability beat complexity rules. A long random passphrase of unrelated words usually scores far higher than a short string with symbols swapped in.

Is it safe to test my real password?

Yes — the whole check happens in this tab with no network request, so the password you type is never sent to a server or stored anywhere.

Related tools

Security Vault tools

Web Crypto · jose · no telemetry

Technical transparency

SafePaper is built so your PDFs are processed in your browser, not on SafePaper servers. The sections below explain this in plain language.

Hosting & delivery

  • The site is a Next.js (App Router) application. Production is static HTML, JavaScript bundles, CSS, and assets—served like any modern front-end (e.g. on Vercel).
  • There is no Route Handler, no pages/api, and no server action that accepts your PDF for processing. We do not operate an upload endpoint for document bodies.

Runtime (your machine)

  • UI is React 19 + TypeScript, styled with Tailwind CSS, with motion via Framer Motion where noted in the interface.
  • Dropped files are read with the browser File API into ArrayBuffer / Uint8Array and kept in client-side React state (a shared provider across tool pages in one visit). The visible queue is also mirrored to sessionStorage when it fits browser limits so a refresh in the same tab can restore filenames and bytes without contacting a server.
  • Heavy merge, split, organize, compress, crop (CropBox and multi-region PDF exports), and redact PDF output runs in a dedicated Web Worker (pdf-operations.worker.ts, compress-pdf.worker.ts, bookmarks-outline.worker.ts, extract-embedded-images.worker.ts, crop-pdf.worker.ts) so the main UI thread stays responsive. Buffers are passed with postMessage + Transferable where supported to avoid extra copies.
  • Organize's optional duplicate-page scan runs in pdf-duplicate-pages.worker.ts with pdf.js + OffscreenCanvas—still only on your device.

Security Vault

  • Security Vault (/security) runs JWT decode, hashing, AES file encrypt, key generation, TOTP, bcrypt, and Shamir sharing with Web Crypto and jose in your tab only.
  • Optional site analytics and the consent banner are disabled on Security Vault routes even if you opted in elsewhere—so secrets pasted here are not on pages that load Vercel Analytics.

Share Desk (peer-to-peer)

  • Share Desk (/share) transfers files with WebRTC data channels directly between two browsers. SafePaper does not store or process file bytes on our infrastructure.
  • A separate WebSocket signaling service (configured via NEXT_PUBLIC_SIGNALING_URL) relays SDP offers/answers and ICE candidates so peers can find each other. That relay carries connection metadata only—not your file contents.
  • Large receives stream into OPFS via opfs-writer.worker.ts so the main UI thread stays responsive. Senders read files in 64KB slices with data-channel backpressure.
  • Peers may use Google's public STUN (stun:stun.l.google.com:19302) to discover network paths. Optional TURN env vars (NEXT_PUBLIC_TURN_URL, etc.) can relay traffic on restrictive networks—that is separate third-party network traffic, not a SafePaper file upload.

PDF stack

  • Structural PDF work (merge order, page extraction, rotation, removal) runs in the worker path described above.
  • Optional password protection applies AES-256 encryption on the main thread after the worker returns bytes, using the browser's Web Crypto API. Your open password is not sent to any server.
  • Previews and raster export (PNG images and plain-text extraction) use a canvas-based PDF renderer in a separate worker. The preview worker script is served as static /pdf.worker.mjs from this site. CMaps, standard font metrics, ICC profiles, and WASM helpers for pdf.js live under /pdfjs/ (copied from pdfjs-dist on npm install) so workers can fetch glyph data from the same origin.
  • That preview worker is separate from the merge/split/organize worker; both use Web Workers and stay entirely on your device.

Network & storage

  • Over the wire you should see requests for the app shell, JS chunks, CSS, fonts (next/font self-hosted subsets), icons, the PDF preview worker script, and (after npm install) same-origin OCR assets under /tesseract/—not outbound uploads of your document to SafePaper for processing.
  • Downloads use normal browser mechanisms (Blob / URL.createObjectURL) initiated by you.
  • By default, tools do not persist your PDFs to SafePaper storage; lifetime is in-memory for that tab session (and the shared client state resets when you leave the tool area for the home page).
  • Storage Desk (/storage) is the one place where files are kept on purpose—and it is always end-to-end encrypted. A single passphrase derives an AES-256-GCM key with Argon2id inside a Web Worker; the key stays in memory only and is never written to disk or sent anywhere. File bytes and metadata (titles, categories, filenames, search embeddings) are encrypted before they touch any backend.
  • You choose the backend: Browser (OPFS + IndexedDB on this device) or bring-your-own S3 (Cloudflare R2 or any S3-compatible bucket, reached directly from your browser via SigV4). With BYO-S3, only opaque ciphertext—including the synced catalog.json index and a vault.json manifest (a non-secret salt + Argon2 parameters + an encrypted verifier, so a second device with the same passphrase can derive the same key)—lands in your bucket; SafePaper never receives it, and neither the key nor your passphrase is ever stored.

Tool-by-tool: where work runs

Tool / areaWhere work runsExtra network
Merge, split, organize, protectBrowser + workersApp shell only
Compress, redact, cleanBrowser + workersApp shell only
Export (PNG / JPEG / text)Browser (pdf.js canvas)App shell only
Forms, watermark, page #, insertBrowser (pdf-lib)App shell only
OCRBrowser (pdf.js + Tesseract)Same-origin WASM/worker/lang after postinstall (no third-party OCR CDN)
Duplicate scan (Organize)Browser worker (pdf.js)App shell only
Share Desk (P2P)Browser WebRTC + OPFS workerSignaling WebSocket + STUN (optional TURN) — no file bytes to SafePaper
Media StudioBrowser + FFmpeg WASM (lazy) + image workersSame-origin FFmpeg under /vendor/ffmpeg/
Data ZoneWeb Workers + DuckDB-wasm + OPFS queuesDuckDB bundles may fetch from jsDelivr on first SQL use — not your table rows
Security VaultBrowser Web Crypto + jose (no upload)Analytics disabled on these routes
AI Desk (RAG)Embedding + chat workers; IndexedDB indexOne-time model weight downloads (Transformers.js / WebLLM CDN)
Record DeskCapture + OPFS mux; Whisper workerWhisper ONNX/WASM may fetch from jsDelivr on first caption run
Vision StudioImage inference worker (ONNX / Transformers.js)One-time model weight downloads (Hugging Face / jsDelivr); images stay local
Audio LabFFmpeg WASM worker + Web Audio; Whisper for transcriptionOne-time FFmpeg/Whisper asset downloads; audio samples stay local
Health Deskdicom-parser + canvas; pure-JS HL7/FHIR; localStorage lab historyNone — scans, records, and lab data are parsed and stored entirely on-device
Scan DeskCamera + canvas image pipeline; Tesseract OCR; pdf-lib exportSame-origin OCR WASM/worker/lang only; scans stay on-device
Diagram DeskMermaid + Graphviz (WASM); canvas rasterize for exportOne-time Graphviz WASM fetch; diagram source stays local
Handwriting DeskCanvas render; MediaRecorder + FFmpeg WASM for videoSame-origin fonts + one-time FFmpeg assets; text stays local
Photo DeskCanvas pixel ops; heic-to WASM decode; RAW preview parseOne-time HEIC WASM assets; photos are edited & encoded on-device
Resume Desk@react-pdf render; pdf.js text extract; localStorageApp shell only; resume data stays in your browser's local storage
Email Deskpostal-mime / msgreader / TNEF parse; DOMPurify + sandboxed iframe (CSP blocks remote); @react-pdf renderApp shell only; email files are parsed in your browser, remote images & trackers blocked by default
Password Deskkdbxweb + hash-wasm Argon2; zxcvbn strength; otpauth TOTP; crypto.getRandomValuesApp shell only; KeePass .kdbx vaults are decrypted & edited in your browser — master password never leaves the tab
Archive Deskzip.js + fflate in archive workerApp shell only (central directory parsed locally)
Data Roomcrypto-packager worker + offline HTML exportSame-origin /dataroom-template.html at build time
Storage DeskArgon2id + AES-256-GCM crypto worker; OPFS + IndexedDB; on-device labeling/embeddingsNone for Browser backend. BYO-S3 sends only opaque ciphertext straight to your own bucket (SigV4) — never to SafePaper

“App shell only” means HTML/JS/CSS/fonts and static assets from your host—no SafePaper API that accepts PDF bodies. A production service worker precaches the home page, PDF preview worker, and vendored OCR files for calmer offline reloads after the first visit.

Offline & limits

  • After the app has loaded once, cached bundles mean the core tools can keep working offline for files already held in memory—subject to browser cache eviction.
  • Practical limits are those of the device: available RAM, CPU, and browser tab limits. Malicious PDFs are still a local execution concern the same way opening a file in any desktop viewer is; we do not add a separate server-side malware scan because files never leave your machine for our processing.

Design rule

Zero server uploads for PDF work. New tools are expected to follow the same model: browser-first, worker offload where needed, and no silent exfiltration of document bytes to SafePaper infrastructure.

Privacy status

See what this page loaded. Your files stay on your device.

Live privacy status

Your secrets stay on your device. Analytics are off on this workspace.

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