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Full spreadsheet engine
Univer-based engine with multi-sheet workbooks, formulas, formatting, real-time multiplayer co-editing, data validation. .xlsx import with progress feedback, autosave with status indicator, manual save shortcut.
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Application · uSheet
Spreadsheets.
Encrypted by default.
Spreadsheet editor
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Capabilities
What you can do with Spreadsheets.
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Import / export legacy Excel files
Validation rules preserved across .xlsx import/export. Work with colleagues who still use Excel without losing structure.
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Side AI for transformations
The AI assistant panel can apply transformations to selections — pivot, normalize, summarize. AI runs against your provider, on your keys.
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Protection
Security for Spreadsheets.
Content in Spreadsheets is inside the end-to-end encrypted envelope: it is encrypted in your browser before it is transmitted, and the server stores ciphertext it holds no key for.
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Post-quantum cryptography by default
All authentication and key exchange uses NIST-standardized ML-DSA-65 (FIPS 204) signatures and ML-KEM-768 (FIPS 203) key encapsulation. There is zero RSA, zero elliptic-curve, zero classical-only crypto in the authentication path. Defeats store-now-decrypt-later attacks.
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End-to-end encryption on your device
Every payload is encrypted in your browser using XChaCha20-Poly1305 (RFC 8439) with a 192-bit nonce and a Poly1305 authentication tag. The plaintext exists only in your tab's memory. When you close the tab, the plaintext is gone.
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The server holds ciphertext it cannot open
For Spreadsheets content the server only ever stores ciphertext and public keys. It cannot decrypt your data — by architecture, not by promise: there is no backdoor, no master key and no key escrow, because no key that would open it ever reaches the server.
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Your keys stay on your device
Your private keys are derived in your browser from three secrets only you control, and are held in memory for the session only — never written to browser storage, never sent to the server. A new device derives the same keys locally from the same three secrets.
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Mechanics
How Spreadsheets works.
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Open Spreadsheets in your browser
UltimaOS runs in any modern browser — Chrome, Firefox, Safari, Edge. Nothing to install. Sign in by re-entering the three secrets your keys are derived from, and the same keys are rebuilt locally on whatever device you are using.
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Your data is encrypted before it leaves your device
Sending a message, uploading a file, writing a note — the content is encrypted with XChaCha20-Poly1305 and authenticated with an ML-DSA-65 signature before any byte crosses the network boundary.
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The server stores ciphertext and returns it on demand
The server keeps an opaque blob it has no key for. When you open Spreadsheets, those blobs are streamed to your device, decrypted locally and rendered. Plaintext exists only in your tab.
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Changes follow you across devices
Any change you make is uploaded and picked up by every other device you are signed in on, so Spreadsheets looks the same wherever you open it.
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Inside the suite
How Spreadsheets fits in the suite.
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Documents
Convert any Spreadsheet range into a Document table. Formatting and validation rules carry over.
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Boards
Cards can attach Spreadsheets as data tables. Formulas recalc on edit.
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Files
Spreadsheets imports legacy Excel files from Files. Validation rules are preserved.
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Account
Spreadsheets are encrypted in your Personal Storage layer. Recovery via Account covers Spreadsheets too.
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Get started
Get started with Spreadsheets.
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Open Spreadsheets in your browser
UltimaOS runs in Chrome, Firefox, Safari and Edge. Nothing to install. Sign in with your passphrase to derive your private key locally.
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Open the workspace and launch Spreadsheets
The launcher shows every app. Spreadsheets is right there with its capsule video preview. Click to open.
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Connect it with the rest of the suite
Spreadsheets works alone, but it shines when combined with the rest of the UltimaOS apps. Same identity, same workspace, one place to work.
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Frequently asked
Questions about Spreadsheets.
Is Spreadsheets end-to-end encrypted?
Short answer
Yes. All content in Spreadsheets is encrypted in your browser using XChaCha20-Poly1305 with a fresh key per item. The UltimaOS server only ever stores ciphertext and public keys — it cannot decrypt your data, no matter who asks.
What cryptography does Spreadsheets use?
Short answer
Spreadsheets uses the same post-quantum stack as every other UltimaOS app: ML-DSA-65 (FIPS 204) for authentication, ML-KEM-768 (FIPS 203) for key encapsulation, XChaCha20-Poly1305 (RFC 8439) for symmetric encryption, and HKDF-SHA256 for key derivation.
Can I use Spreadsheets on multiple devices?
Short answer
Yes. Sign in on any device by re-entering your three secrets and the same keys are derived locally, so your Spreadsheets content follows you. Changes sync live across all signed-in devices.
Is Spreadsheets GDPR-compliant?
Short answer
Yes. UltimaOS is built and operated in the European Union by an EU company. The architecture is GDPR-compliant by design — encrypted data, EU-only infrastructure, no US CLOUD Act exposure, no advertising, no third-party trackers. See the GDPR page for the full breakdown.
How much does Spreadsheets cost?
Short answer
UltimaOS is free for individuals and families — permanently, not as a trial. Organizations pay per seat once early access ends, and that is what funds the free accounts. There is no per-app add-on.
Can I export my Spreadsheets data?
Short answer
Yes. UltimaOS supports encrypted export of all your content for backup and portability. The export is encrypted to a key you control; you can store it on your own infrastructure or in a personal encrypted backup.
Can I open .xlsx files I receive from outside?
Short answer
Yes. Spreadsheets imports legacy Excel files (with validation rules preserved) and exports to .xlsx when you need to share with colleagues who are not on UltimaOS.