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Overview
SumSheet — what it isCapability map next to ExcelArchitecture: four layers and objectsWhat happens from open to saveStrengths and tradeoffs
Getting started
Installing SumSheetQuick start: your first project
Guides
How the API session worksRequests used in the exampleResponding to clicks and the context menuIntegrating into an applicationEmbedding kit: structure, events, menuSurface eventsDiagnosticsVerified script
Runtimes
The core in the browser through WebAssemblyA separate core process alongside your applicationSumSheet as a server-side processorPhone and tabletRuntime environments and the end-to-end scenario
Contract and boundaries
Readiness checklistFrom concept to pilotSumSheet version history
Examples
Live example: a budget spreadsheetSumSheet examplesMinimal sheetSheet with the ribbonEmbedding into a third-party pageA million rowsCrosshairRead-onlyCustom headersSheet without header stripsCustom menu itemCustom keyboard shortcutCustom languageDrop a workbook hereTwo people in one documentAssistants drive the sheetCustom eventHyperlinkFind and replaceNotesSheet outlinePage layoutAllow editing rangesWorkbook linksHeadless
Reference
SumSheet referenceSumSheet transport and message formatSumSheet session and conventionsWhat you can do with each formatSession and workbookCells and rangesSheetsPrinting and layoutFormulas and calculationFormattingData, filters, and objectsPivot tablesPower Query: M expressionsPower Query: connectorsPower Query: queries and stepsPower Query: tables from queriesPower Query: execution and progressPower Query: trust and privacyPower Query: external mashupsVBA and macrosProtection and reviewTypes: session, workbook, and sheetsTypes: cells and rangesTypes: formulas and calculationTypes: formattingTypes: data and sheet objectsTypes: pivot tablesTypes: charts and graphicsTypes: printing and page layoutTypes: Power QueryTypes: VBA and macrosTypes: protection and reviewTypes: general and utility

Strengths and tradeoffs

What the architecture gives you and what it costs — an honest list, no marketing.

Architecture is always a trade: every property is paid for with something else. Below are both sides of the trade, with no cherry-picking. First what the product’s design gives you, then what it costs and what you’ll have to do.

What the product’s design gives you

Section titled “What the product’s design gives you”
Strength What it gives you
A single owner of meaning — the Rust core The browser, the desktop app, and the server wrapper understand operations the same way.
One operations contract You can change the interface and the transport without rewriting the spreadsheet engine.
Computing by visible area A large workbook never unfolds entirely in the browser — only what’s needed right now is computed and drawn.
Running on your own machine, inside your own perimeter Documents can stay inside your infrastructure and never leave.
Explicit refusals and revision checking An error or someone else’s concurrent edit produces a refusal before the change, not a half-corrupted file.
A surface under your brand The brand, the user journey, and the customer relationship all stay yours.

What it costs

Section titled “What it costs”
Limit What you’ll need
The public developer kit still needs to be separated from the internal contract. Stable package names, versions, compatibility rules, examples, and a version support period.
The server wrapper isn’t a ready-made multi-tenant platform. A gateway, a task queue, isolation, quotas, secret storage, metrics collection, and availability commitments.
The mobile kit is an editor page, not a library for your own screens. Ready-made apps for phone and tablet are released, and the viewing kit is assembled from the same build: the core, the page, and the bridge. Your own screens in Swift and Kotlin on top of the bare core are separate work; there’s no public kit for it (Phone and tablet).
The core in the browser is limited by memory and by the browser’s rules. Decisions on background threads, vector computation (SIMD), and multithreading, a fallback route, and calculated memory limits.
Matching Excel is finite and reached in stages. An agreed capability matrix; what’s unsupported is honestly hidden or disabled, not made to look like it works.
Two parts to the runtime complicate releases. Matched versions of the web part and the core, checksums, signing, and the ability to roll back to a previous version.

Next

Section titled “Next”

Documentation assistant

Answers are assembled from the documentation and may be inaccurate — check the sources.