What is LogiSheets?

LogiSheets is a spreadsheet engine written in Rust and compiled to WebAssembly. It reads, edits and writes real .xlsx files, and the same engine runs in the browser, on Node.js, and natively in Rust.

That part is ordinary. Here is the part that is not.

Where AI and people work together

A spreadsheet is the most widely understood tool people have for working with data. It is also a bad thing to hand a machine.

Everything that makes a sheet readable to a person is a habit, kept in their head. Where the table starts and stops. That the first row is headings. That column D is a percentage, and the empty rows at the bottom are padding rather than missing data. A person takes all of this in at a glance and never thinks about it again.

A model sees none of it. Give an agent a plain grid and it has to guess the structure, then act on the guess. When the guess is wrong nothing breaks — you get a believable number in a believable cell, and somebody finds out weeks later.

LogiSheets writes those habits into the file, so one document works for both readers:

• The person sees an ordinary grid, and gets a real .xlsx.
• The agent sees tables it can name, columns whose type and meaning it can read back, rows it can address by key, rules that say when a value is wrong, and limits on what it may change.

There is no separate "AI copy" of the data, and no chat box bolted to the side. It is one file with enough structure written down that both can work in it. That structure is a block, and everything else here is built on it.

An agent reaches the engine three ways, all of them the same API underneath:

• Watson, the assistant built into the web app.
• logisheets-logician, the agent toolkit — tool definitions that drive a real workbook. No host dependencies, so it runs in the browser or on Node.
• logisheets-mcp, which puts the engine behind the Model Context Protocol for Claude Desktop, Cursor, or your own agent.

What else is different

It really is Excel

LogiSheets speaks .xlsx natively — formulas, styles, merged cells, several sheets. A file it writes opens cleanly in Excel, and a file Excel wrote loads without losing anything. You do not trade compatibility for the features below. You get both.

Blocks: tables that know they are tables

In a plain spreadsheet a cell is only a coordinate. C5 does not know it belongs to the line-items table, so a formula pointing at it breaks the moment somebody inserts a row.

A block is a region of the sheet with a stable identity, and optionally a schema — named columns, a key column, declared types. Once a region has those, you stop addressing cells and start addressing data: the revenue field of the 2024-Q1 row of the income_statement block. That address survives every insert, delete and sort.

→ Blocks

Crafts: small apps that live in the sheet

A spreadsheet is generic; your work is not. A craft is a small application that runs inside LogiSheets — a pricing form, a what-if calculator, a simulator. You write the logic once and it reaches the browser UI, a headless runtime, and the AI assistant.

→ Crafts

Three ways to use it

The three build on each other, so pick the lowest one that does your job.

1. As a spreadsheet library

Read, edit and write .xlsx from code. The same core API in three packages:

Package	Language	Where it runs
logisheets-rs	Rust	Native
logisheets	TypeScript (WASM)	Node.js
logisheets-web	TypeScript (WASM)	Browser

You work with a Workbook and Worksheet, read cells, and send edits as batched transactions. Right for file conversion, report generation, server-side processing, or driving your own UI.

→ Read & write Excel files

2. As a spreadsheet in a web page

If you want a working grid in the browser — selection, scrolling, editing, sheet tabs — use logisheets-engine. It is a canvas UI built on logisheets-web, using OffscreenCanvas and a Web Worker so rendering never blocks the page.

npm install logisheets-engine logisheets-web

import {Engine} from 'logisheets-engine'
import 'logisheets-engine/style.css'

const engine = new Engine()
engine.on('ready', async () => {
    engine.mount(document.getElementById('spreadsheet')!)

    const buf = await fetch('workbook.xlsx').then((r) => r.arrayBuffer())
    await engine.loadFile(new Uint8Array(buf), 'workbook.xlsx')
})

→ Add a spreadsheet UI

3. With blocks and crafts

This is the level that makes LogiSheets more than a grid: structured regions your own code, your crafts, and an agent can all read and write reliably.

→ Blocks and Crafts

Where to go next

• New to the engine? → Read & write Excel files
• Want a grid in a web app? → Add a spreadsheet UI
• Storing real data in a sheet? → Blocks
• Building a feature on top? → Crafts
• How those two combine → Putting it together