Casual Sheets vs OnlyOffice — which open-source office suite to self-host

OnlyOffice Document Server is the obvious comparison if you’ve shortlisted “open-source self-hosted office suite” and you want to serve real spreadsheets. It’s been around since 2009, ships an all-in-one binary for Linux + Windows + Docker, and renders .docx

• .xlsx + .pptx with high fidelity.

Casual Sheets is the newcomer (v0.2.1, ~6 months old). This comparison is honest about where OnlyOffice wins.

At a glance

	Casual Sheets	OnlyOffice Document Server
License	Apache-2.0 (truly permissive)	AGPL-3.0 + commercial offering
File formats	.xlsx, .ods, .csv, .tsv	.docx, .xlsx, .pptx, .odt, .ods, .odp, others
Scope	Spreadsheets only (sister projects for docs + slides)	Full suite — docs + sheets + slides + forms
Docker image size	~50 MB compressed (single-arch)	~1.5 GB (multi-arch, bundles everything)
RAM at idle	~100 MB	~1.5 GB
Backend stack	Fastify + Hocuspocus (Node)	C++ DocService + Node + RabbitMQ
Sync engine	Yjs CRDT	OT (Operational Transform)
Co-edit ceiling	~500 active docs / 1500 WS per process (measured)	Higher per process, but heavier per-doc
Auth	Built-in JWT + admin panel	JWT (token in URL) + integration hooks
Integration model	Direct UI + WOPI host	WOPI/JWT integration — designed to embed into Nextcloud/Seafile/etc.
Standalone use	Yes — first-class	Designed to be embedded; standalone UI is utilitarian
Maturity	v0.2.1 · 6 months	v8+ · 15+ years
Mobile	Web viewer + light editor	Native iOS + Android apps + web

License — the elephant in the room

OnlyOffice is AGPL-3.0 for the open-source edition. If you embed it in a product you ship to anyone (including SaaS users) you have to release your full application’s source under AGPL. That’s a non-starter for most commercial use; OnlyOffice sells a commercial license to escape it.

Casual Sheets is Apache-2.0. Embed it, fork it, wrap it, ship it to customers — no copyleft, no commercial license to buy. This is the single biggest reason to pick Casual Sheets if you’re building on top.

If you’re self-hosting only for your own use (employees, a closed team) and never plan to redistribute, the AGPL doesn’t affect you.

Architecture — different design centers

OnlyOffice is built to be embedded into a host. It assumes your authentication, your file storage, your URL structure. WOPI is the primary integration surface; the standalone UI is functional but clearly a secondary concern.

Casual Sheets is built to be used directly OR embedded. The standalone UI is a first-class web app (Office-style ribbon, home gallery, recent files); the WOPI host integration is there too if you want to plug it into Nextcloud or another host, but it’s not the only path.

If your shape is “I want to give my users a great spreadsheet right now,” Casual Sheets makes that one-line easy. If your shape is “I have a document-management system and I want a spreadsheet renderer inside it,” OnlyOffice’s WOPI-first design fits better.

.xlsx fidelity, measured

File feature	Casual Sheets	OnlyOffice
Cell values + formats	✅	✅
Formulas	✅ (Univer formula engine)	✅
Number formats	✅	✅
Pivot tables	✅ (re-emit + drill-down)	✅
Conditional formatting	✅ common cases	✅ more presets
Charts	✅ 8 types via ECharts	✅ more types, native rendering
Data validation	✅	✅
Sparklines	✅	✅
.xlsm VBA passthrough	✅ byte-equal — captures xl/vbaProject.bin and re-emits	✅ Pro edition
Pivot cache passthrough	✅ 54 / 54 audit pristine	✅
Page setup / print	✅	✅
Defined names	✅	✅

Casual Sheets has a 54-probe round-trip audit checked into the repo. OnlyOffice has a decade of bug fixes on harder edge cases (complex array formulas, esoteric chart types). For mainstream business spreadsheets both round-trip without surprise. For your most exotic .xlsx files, OnlyOffice has more tested surface.

Resource footprint

OnlyOffice Document Server ships a kitchen-sink stack: C++ document processor, Node UI server, RabbitMQ for job queuing, Redis, Postgres. ~1.5 GB Docker image, ~1.5 GB RAM at idle, multiple processes per host.

Casual Sheets is a Fastify + Hocuspocus binary plus the built web SPA. ~50 MB image, ~100 MB RAM at idle, single Node process. Single-doc memory is ~370 KB; you can fit thousands of active docs on an 8 GB box.

If you’re sizing for “tiny VPS that just works,” the Casual Sheets footprint is roughly 30× smaller. If you have hardware to spare and want the integrated suite, OnlyOffice’s larger footprint isn’t an issue.

When to choose what

Pick OnlyOffice if:

• You need .docx + .xlsx + .pptx in a single binary today.
• You’re embedding into a document-management system (Nextcloud, Seafile, ownCloud) that already has WOPI integration.
• You need native mobile apps.
• The AGPL doesn’t affect your distribution model (internal use, or you have an AGPL-compatible product, or you’re buying the commercial license).
• You want the most-tested edge-case .xlsx fidelity.

Pick Casual Sheets if:

• License matters — Apache-2.0 lets you embed, fork, or ship without copyleft obligations.
• You only need spreadsheets right now (Casual Editor and Casual Slides are sister projects on their own roadmap).
• You want a small footprint — a $5/mo VPS comfortably handles a small team.
• You’re building on top of a spreadsheet and need clean extensibility.
• You want the source to be readable in a weekend (~10k LOC web + ~3k LOC backend, vs OnlyOffice’s hundreds of thousands).

Both are real choices. The AGPL question usually decides for you.

What about the other two products?

Casual Editor (.docx) and Casual Slides (.pptx) are sister projects in the same suite. Editor is at M1 backend live with the WOPI host integration; Slides is at v0.0.0 pre-tag (fidelity-mature, infra-immature). Neither matches OnlyOffice’s maturity on those formats yet.

If you need the full office suite today, OnlyOffice is the right answer for .docx + .pptx while Casual Sheets handles .xlsx. As Casual Editor and Casual Slides reach v0.2.x parity, the suite story closes.

Try Casual Sheets

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

Compare image size, RAM use, and startup time directly against an OnlyOffice Document Server container — the differences are substantial.