GridPath

Real Excel files, in your web app and in your agent.

GridPath opens the .xlsx files people already have and calculates every formula with a Rust engine. AI can edit the files, with a review step. The saved file is the same one that was opened: charts, pivots, VBA and add-in data come back byte-identical.

The engine, the in-place saver and the gridpath package (the web spreadsheet and the MCP server) are open source under Apache-2.0. The desktop app is source-available under the FSL-1.1-Apache-2.0 (details).

In your web app

npm install gridpath react react-dom

import { Spreadsheet, httpStore } from "gridpath";

const store = httpStore({ url: "/api/books" }); // or leave `store` out to save in the browser

<div style={{ height: 600 }}>
  <Spreadsheet
    store={store}
    documentId={book.id}
    onReady={(sheet) => (sheetRef.current = sheet)}
    onError={(err) => console.error(err.code, err.message, err.hint)}
  />
</div>;

Without any further code, users get:

• a formatting toolbar;

• saving as they work, with a status that says where: "Saved in this browser" or "Saved to your account";

• version history and a Recent list;

• Download as .xlsx;

• an "AI changes" panel for reviewing an agent's edits.

Your code gets:

• a small API: getCell, setCell, save, open, openStored…, with stated contracts;

• typed errors, each with a code and a hint you can show;

• the agent tools for your own model (sheet.ai).

When saving to your backend fails, nothing is lost. The edits wait in the browser and the save is retried.

• The guide and API reference

• A complete Next.js app, with auth and REST routes

• The live demo

Against the spreadsheet components a web app would otherwise embed (on real models in Chromium, method and results):

• Opening. GridPath opens a 1.4 MB analyst model and recalculates it in 0.8 s. SpreadJS takes 3.6 s; Handsontable with HyperFormula and ExcelJS takes 1.9 s.

• Saving. GridPath keeps 75 of the file's 76 parts byte-identical. The others drop custom XML, printer settings and more.

• Scale. On a model with 2.3M cells, SpreadJS crashes the tab. GridPath opens it and updates the dependents of an edit in 2.7 s.

Related MCP server: Excel MCP Server

In your coding agent (MCP)

claude mcp add gridpath -- npx -y gridpath mcp --review-required

Your agent edits the real .xlsx through GridPath's tools:

• describe, find, read and write;

• run_script;

• structural operations (rows, columns, sheets).

Every change returns a readback and a review link, which shows each changed cell before and after; accept or reject per batch, then save.

• Nothing is written until you save.

• With --review-required, only the review page can save.

• No Python, no LibreOffice, no Excel needed.

Details, host config snippets and the tool list: packages/gridpath/README.md.

The same edit takes a fraction of the time and tokens, because the agent calls spreadsheet tools instead of writing and debugging scripts. Claude Code (Sonnet 5.5) on a real 1.4 MB, 55,000-formula analyst model, with the same prompt with and without GridPath:

Both lanes got every edit right. The difference is time, tokens, and seeing the diff before anything is saved. The full runs, including the ones we lose, are in the evals repo.

Desktop app

Open a .xlsx, type what you want, review the diff, accept it. Multiple workbooks side by side, each with its own agent; other files attachable as read-only references. Your file never leaves your machine, and it works with the Claude or ChatGPT subscription you already pay for.

Download GridPath

What the app does

• Multi-workbook — Workbooks side by side, each with its own agent. Attach others as read-only references.

• Reversible changes — Diff-first edits. Accept, reject or use ⌘Z. Nothing saves until you say so.

• Spreadsheet-native harness — With the same model, GridPath ran 3.9–14× faster in our benchmarks and used 95–96% fewer output tokens on edit tasks.

• Workbook fidelity — Surgical saves rewrite only what changed; charts, pivots, formatting, VBA and plugin data stay intact.

• Formula-first — Writes formulas, not pasted numbers, so models stay live.

• Local-first — Your .xlsx stays on disk. Only your prompt and the cells the agent needs go to Claude or OpenAI.

How the desktop app compares

Best-effort comparison as of September 2026. The "preserves" and "diff" rows for coding agents are measured, not inferred — see the benchmark repo. On the August 2026 models a headless coding agent silently dropped parts of a workbook in 2 of 5 edit runs; on Sonnet 5.5 (September 2026) it preserved every part in all of our runs by choosing XML surgery on its own. GridPath preserves them by construction, not by the model's judgment on the day.

Project status

Under active development.

• The web package is at 0.4. Not yet supported: drawing charts in the grid (they are kept in the file, but not shown), data-validation dropdowns, real-time collaboration.

• For agents, editing existing workbooks is the strongest path, and the one benchmarked continuously. Building large multi-sheet models from scratch works but is still improving. The benchmark repo publishes those results too, including the ones we lose.

License

Open source (Apache-2.0, LICENSE): the calculation engine and in-place saver (crates/, the IronCalc fork in vendor/ironcalc), the gridpath package (packages/gridpath, packages/grid: the web spreadsheet, the agent tools, the MCP server), the examples and the evals. Use them in anything, commercial or not, including closed-source products.

Source-available (FSL-1.1-Apache-2.0): the desktop app (src/, src-tauri/) and the hosted services (proxy-server/, the desktop app's sign-in, and marketing/, the site), each with its own LICENSE file. You can read, modify and run them for any use except a competing product; each release becomes Apache-2.0 two years after it ships.

"GridPath" and the logo are trademarks (TRADEMARKS.md). Releases of the gridpath npm package before 0.2.0 were FSL-1.1-Apache-2.0.

Build from source

Requires Node 20+, Rust stable via rustup, and your platform's Tauri prerequisites.

npm install
npm run tauri dev

npm run tauri build produces a local unsigned build. On first launch, connect Claude with OAuth or an API key, or use the ChatGPT sign-in flow. Credentials stay in the local SQLite database.

Architecture

GridPath uses Tauri 2 with a Rust core, React and TypeScript, a vendored IronCalc fork (MIT/Apache-2.0), and SQLite. The surgical .xlsx patcher is in src-tauri/src/engine/workbook/xlsx_patch/, the agent loop in src-tauri/src/engine/spreadsheet_agent/, and the benchmark harness in eval/.