Casual Sheets vs Excel Online — open-source alternative you can self-host

If you searched “open source Excel Online alternative” or “self-host alternative to Microsoft 365”, this page covers Casual Sheets honestly against Excel Online.

The short version: Casual Sheets is the right answer if you want to keep .xlsx workflows on your own infrastructure without a Microsoft account. Excel Online is the right answer if you’re committed to the Microsoft 365 ecosystem.

At a glance

	Casual Sheets	Excel Online (Microsoft 365)
License	Apache-2.0 — open source	Proprietary SaaS
Hosting	Self-host via Docker	Microsoft-hosted only
Price	Free; pay your own hosting (~$5–50/mo)	Microsoft 365 Personal $7/mo · Business Basic $6/user/mo
Microsoft account	Not needed	Required
Native file format	.xlsx (round-trips byte-equal with .xlsm)	.xlsx (native)
File compatibility	.xlsx, .ods, .csv, .tsv	.xlsx + import for many
.xlsm macros	Round-trip byte-equal (we don’t execute VBA)	Web doesn’t run VBA either
Real-time co-edit	Yes (Yjs + Hocuspocus)	Yes (Microsoft’s stack)
Formula support	Univer formula engine (~500 functions)	Full Excel function library (~500 + dynamic arrays)
Charts	8 types · trendlines · sparklines	50+ types · richer customisation
Pivot tables	Yes, with drill-down	Yes, mature
Power Query / Power Pivot	No	Yes (Microsoft 365)
Data location	Your server	Microsoft’s servers (US/EU/etc. by tenant)
Offline	Yes (single-user mode)	Limited (web only — full offline is desktop Excel)
Mobile	Web viewer + light editor	Native iOS + Android apps
Maturity	v0.2.1 · 139 unit + 357 e2e tests	35+ years of Excel lineage
Integration	WOPI host (works with Nextcloud / SharePoint clones)	SharePoint, Teams, OneDrive, Power BI

Where Casual Sheets wins

• No Microsoft account required. Excel Online is locked behind a Microsoft account; the free tier is live.com/outlook.com, business use needs a Microsoft 365 tenant. Casual Sheets has zero identity requirement — anonymous rooms work, or wire up JWT for authenticated access.
• Data stays on your servers. Compliance, sovereignty, paranoia — whatever the reason, docker run puts the whole stack on your hardware. Some jurisdictions (Germany BSI, India MeitY, certain US government contractors) require data residency that Microsoft data centres don’t always match.
• .xlsm macros survive the round-trip. Excel Online silently strips VBA on save (it’s a web app; it can’t execute VBA). Casual Sheets captures xl/vbaProject.bin and re-emits it byte-equal — so the next desktop user opening the file still has working macros. Same operational result, but you don’t need a desktop Excel license to preserve the VBA.
• Predictable cost. Microsoft 365 Business Basic for 100 users is $7 200/year. Casual Sheets for the same workload runs on a $48/mo DigitalOcean droplet — $576/year, total. The 13× difference matters for self-funded teams.
• Apache-2.0. Fork it, embed it, wrap it. No licensing negotiation.

Where Excel Online wins

• Full Excel function library. Microsoft has 35 years of formula refinement; some niche functions (LET, LAMBDA, XLOOKUP edge cases, dynamic arrays with implicit intersection) aren’t fully in Univer’s engine yet.
• Power Query / Power Pivot. If your workflow depends on Get & Transform or data models from external sources, Excel Online + desktop Excel is the answer. Casual Sheets has CSV import but no query refresh.
• Chart variety + polish. Excel ships 50+ chart types with presentation-grade defaults. Casual Sheets ships 8 covering the common cases.
• Native mobile apps. Excel for iOS and Android are first-class. Casual Sheets has a web viewer + light editor at ≤480 px; it works but isn’t a native app.
• Deep Office ecosystem integration. SharePoint, Teams, Power Automate, Power BI — if your organisation is Microsoft-heavy, the network effects are real.
• 35 years of edge-case fidelity. Exotic chart types, complex array formula behaviours, certain print layouts — Microsoft has fixed bugs you haven’t even hit yet.

VBA reality check

Neither product runs VBA in the browser. Excel Online silently drops macros on save. Casual Sheets captures and re-emits them byte-equal, so the next time the file opens in desktop Excel, the macros still execute. Same “browser can’t run VBA” reality; different preservation behavior.

If macro preservation matters to your team’s workflow (file flows through web edit → email → desktop Excel run), Casual Sheets is strictly better here.

Self-host complexity, honestly

You need to be comfortable with:

• Docker (single container; multi-arch amd64 + arm64).
• A reverse proxy (nginx, Caddy, Traefik, or Cloudflare).
• Optional Redis for Y.Doc persistence across restarts.
• Raising ulimit -n 65535 for WebSocket connections.
• TLS termination + cert renewal.

If your IT team already runs nginx, they can run Casual Sheets. Excel Online has zero of these — you sign up, you use it.

Cost — real numbers

For ~100 concurrent users, ~30 active docs (small-team shape):

Cost surface	Casual Sheets	Excel Online (M365 Business Basic)
Hosting	$15–25/mo (small VPS + Redis)	$0 (Microsoft-hosted)
Per-user licensing	$0	$6/user/mo = $600/mo for 100 users
Setup time	1 hour	5 minutes per user
Ongoing ops	~1 hour/month	Zero
Total / year	~$300	~$7 200

For ~10 concurrent users (very small team):

Cost surface	Casual Sheets	Excel Online
Hosting	$5–10/mo (tiny VPS)	$0
Per-user licensing	$0	$60/mo for 10 users
Total / year	~$120	~$720

Both ranges; both could be right for you. The break-even is roughly 2 users — past that, the per-seat SaaS billing dominates.

What’s not in Casual Sheets

Being honest about gaps vs Excel Online:

• Dynamic array formulas (FILTER, SORT, UNIQUE, SEQUENCE) — partial support; not all Excel 365 array behaviours.
• LAMBDA + LET — not yet.
• Power Query — not on the roadmap.
• Co-authoring presence avatars with cursors on cells — works, but less polished than Excel’s “name + colour ring on the active cell” treatment.
• Native iOS/Android apps.
• Right-click “Translate” / AI assist — Univer’s command bus supports plugins; no resources allocated to build the integrations.

These all land based on contributor interest; the roadmap is docs/PRODUCTION_PIPELINE.md in the repo.

When to choose what

Pick Casual Sheets if:

• You want to keep data on your servers.
• You want predictable, low cost.
• You don’t want a Microsoft account dependency.
• You’re building on top of a spreadsheet.
• VBA macro preservation matters.

Pick Excel Online if:

• You’re already on Microsoft 365 for everything else.
• You depend on Power Query / Power Pivot / Power BI.
• You need niche Excel-365-specific functions (LAMBDA, etc.).
• You want native mobile apps.
• You don’t want any operational responsibility.

Try Casual Sheets

docker run -p 3000:3000 schnsrw/casual-sheets:latest

Open http://localhost:3000, upload an .xlsx file from your Excel workflow, edit it, save it. Open the saved file in desktop Excel — round-trip should be lossless for the surface we cover (see the 46-probe audit in docs/xlsx-lossiness.md).

Live demo: https://sheet.schnsrw.live/.