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A Python cell is written to xlsx as [MS-XLSX] 2.3.10 specifies: its formula is _xlfn._xlws.PY(i,0|1), where i is the zero-based index of the cell's script in the workbook's Python part and 0|1 the return type, 0 for an Excel value and 1 for a Python object. The part (2.1.23) is xl/python.xml, content type application/vnd.ms-excel.python+xml, related from the workbook part with http://schemas.microsoft.com/office/2023/09/relationships/Python; its root python holds pythonScripts, one pythonScript per Python cell in the order the cells are written, with the code in code. The code keeps its xl() references as text, so the formula has no further arguments. The cell keeps its cached value. A spilling result is written like a dynamic array (cm="1", t="array" ref=...) with the spilled values cached, so other applications show the values (and #NAME? if they recalculate). The reader turns a PY( formula with or without the _xlfn. and _xlws. prefixes into a Python cell. An index names a script of the Python part, and each %Px% in the script becomes the text of the formula's argument x (2.3.10.4). The string-literal form, PY("chunk"&"chunk",0|1), still reads, from the formula's own text so line breaks in the code survive. A formula naming a script the part doesn't hold keeps only its cached value, with a warning: no calculation can evaluate it. The reader keeps the cached spilled values as the cell's result, so a workbook from Excel shows its arrays without running anything. Python errors are cached as #VALUE!, as #SPILL! and #CALC! already are. Native JSON keeps Cell.py whole: code, return type, the last result and the exact error. Calc lays out a Python cell's kept result: Python cells are nodes of the dependency graph that read nothing, and a pass takes a dirty Python cell's result instead of evaluating it, so its array spills, is blocked (#SPILL!) and unblocked, and feeds its dependents exactly like a formula's. An array that is malformed or has more than 1,000,000 cells (only a crafted file holds one) shows #SPILL!. A dirty Python cell is pending in the pass, as a dirty formula is, so a formula, a range read or a cell-by-cell range walk that reaches it before its turn lays it out first rather than reading its old value. Opening a file can't make the app loop over a claimed size: the reader keeps a Python cell's spill range only when it has at most 1,000,000 cells (a range claiming the whole sheet is dropped with its values, as a formula's spilled values are), and io::adopt_python rebuilds results for at most 4,000,000 cells over the whole workbook, with a warning for the cells it skips. The Python part is read up to 64 MB and 1,000,000 scripts, a script is kept up to one character past what a cell may hold, and the cells take at most 64 MB of code from the part in all, since several formulas can name one script. io::enforce_python_limits drops the code of a cell whose code doesn't fit in 8,192 characters as PY(...) (the cell keeps its cached value, with a warning) and a kept result that isn't a well-formed array within the cap, each with its spill range and spilled values, so the sheet and a save no longer show the old spill. Formats that keep PY() as an ordinary formula (xls, xlsb, ods) are adopted the same way. Opening a file runs nothing. The command-sequence fuzzer sets Python cells (code with xl() references, quotes, line breaks, and code at and over the size limit), and its xlsx round-trip check allows the Python errors becoming #VALUE!, which is what the file format stores. Tests: the written formula naming its script, the Python part with its content type and relationship, return types, a spilling table saved as a dynamic array, Python errors as #VALUE!, the round trip of values, code, long code with quotes and line breaks and the error, and no Python part without Python cells; a workbook laid out as the format specifies (an index, a parameter named as %P2%) read as Python cells with their spilled values and saved back with its code in a Python part; the string-literal form; a formula naming a missing script, with and without a Python part; 20,000 cells naming one long script against the code budget; the part's reader and writer (escaping, odd %P tokens, a long script, a repeated parameter); a blocker in the spill area giving #SPILL! and clearing it spilling again; the native JSON round trip; a spill range claiming the whole sheet; the workbook-wide budget; hostile JSON (code over the limit, a result claiming far more cells than it holds); a malformed result that never spills; PY() formulas at 8,079 and 8,080 characters of code. Calc: formulas, MAX, SUM, COUNTA and SUMPRODUCT read a dirty Python cell whose array is blocked before its turn, in a full and an incremental recalculation, and see the array once it is unblocked; enforce_python_limits removes the spill of dropped code and of a dropped result, and keeps a sound one.
GridCraft
Spreadsheets and data; an open-source, high-performance modern spreadsheet application, built in pure Rust.
A fast, open-source, clean-room take on modern spreadsheet workflows. It runs natively on macOS,
Windows, Linux and BSD, and in the browser via WebAssembly.
By the ArtCraft team.
GridCraft on getartcraft.com · ArtCraft · All Crafting Apps
Quarterly Sales Dashboard: a table with a totals row, conditional formatting, sparklines and two live charts — built entirely from GridCraft commands (File → New → Sample).
Note
ArtCraft is a community of artists from all walks of life. Painters, photographers, filmmakers, illustrators, designers, animators, hobbyists, and people who picked up a pencil last week. If you make things, you're one of us. Come say hi on Discord.
A look around · Why GridCraft · Quick start · For agents · Architecture · Roadmap · The Crafting Apps · License and credits
A look around
 Formatting. Accounting formats, cell styles, conditional rules and colour scales, frozen headers and a bar chart. |
 Formulas. 500+ functions, dynamic arrays, LET and LAMBDA, structured table references. |
 Dark mode and the Insert tab: tables, charts, sparklines, pictures, shapes, links and comments. |
 Pivot tables. Field list, filters, layouts, date grouping and show-values-as, saved to and read from XLSX. |
 Charts. Seventeen chart types, Chart Design tab and a Format pane; selecting a chart outlines its source data. |
 Page Break Preview, print settings, and PDF export and printing. |
Why GridCraft
- Familiar. Ribbon, formula bar, Name Box, sheet tabs, keyboard shortcuts, fill handle, point-mode formula entry with coloured references, Format Cells, Paste Special, conditional formatting, tables, charts and more. Everything is right where you expect it.
- Compatible. XLSX is the native format: styles, themes, formulas (including dynamic arrays),
tables, conditional formats, validation, comments, hyperlinks, charts, pictures, sparklines,
pivot tables and print settings round-trip. CSV and TSV too.
Legacy 97-2003
.xlsworkbooks open with their values, formulas and number formats (formatting and objects not yet). XLSB worksheet data can be imported, using saved values instead of formulas. ODS worksheet data can be imported, using saved values instead of formulas. Static pictures can live inside cells, fitting their size and moving with the data. - Capable. A dependency-graph calculation engine with dynamic arrays and spilling, 500+ worksheet functions plus LET, LAMBDA, MAP, REDUCE, SCAN, BYROW, BYCOL and MAKEARRAY, structured table references, a comprehensive number-format language, sort and AutoFilter, Flash Fill, data validation, outlining and subtotals.
- Fast. Copy-on-write workbooks (undo snapshots are nearly free), incremental recalculation, and a virtualised grid that only lays out what's on screen.
- Agent-native. Every ribbon button, menu item, dialog, keystroke and mouse gesture is a command that agents can run over a JSON control channel, an MCP server, or the CLI.
- Everywhere. One Rust codebase for desktop and the web. No subscription, no licence server, no telemetry.
Quick start
cargo run --release -p gridcraft # desktop app
cargo run --release -p gridcraft -- --sample sales # open a sample (sales, budget, grades)
cargo run --release -p gridcraft -- book.xlsx # open a workbook
cargo run --release -p gridcraft -- --sample sales --control 7979 # + JSON control channel
cargo xtask ci # fmt, clippy, tests, assets, layering, wasm
Choose Español under View → Interface language for Spanish formula names, decimal commas, and semicolon arguments. Workbooks, clipboard exchange, and programmatic APIs retain canonical English syntax.
Web
cd apps/gridcraft-web && trunk build --release # → dist/web (serve it with any static server)
cd apps/gridcraft-web && trunk serve --release # http://127.0.0.1:8771 (?sample=sales opens a sample)
You need trunk and the wasm32-unknown-unknown target. Open uses the
browser's file picker (dropping files works too) and Save downloads the workbook.
Ribbon access keys
Press and release left Alt on Windows/Linux/BSD, or press F10 on any platform, then type a sequence below one key at a time. Keytips appear on the supported Home controls and menu items. On macOS, use F10 (Fn+F10 if required by your keyboard); Option remains available for entering accented characters.
| Sequence after Alt/F10 | Action |
|---|---|
H A L / H A C / H A R |
Align left / center / right |
H V S or legacy E S |
Open Paste Special |
H O I or legacy O C A |
AutoFit selected columns |
In Paste Special, T/V/F/C select formats/values/formulas/comments, and E toggles Transpose. Enter applies the selected options; Escape cancels the dialog. These letters also work with Alt held on Windows/Linux/BSD.
Escape backs out one keytip level; Alt/F10 again exits keytips. Clicking, scrolling, or switching windows cancels navigation. Access keys do not start while editing text or using another dialog. This is initial support for these Home and legacy paths; other ribbon commands and full mouse-free navigation remain to be implemented. Browsers or desktop environments may reserve Alt/F10 for their own menus.
Logs
The desktop app writes its log to standard error and to gridcraft.log in the logs folder
next to its settings: ~/.config/gridcraft/logs on Linux and BSD ($XDG_CONFIG_HOME/gridcraft/logs
when set), ~/Library/Application Support/GridCraft/logs on macOS and
%APPDATA%\GridCraft\logs on Windows. Each start moves the previous log to gridcraft.1.log and
that one to gridcraft.2.log, so the log of a run that crashed survives the next start; attach
them to a bug report. A log file stops growing at 16 MiB. By default GridCraft's own crates log
at info and everything else at warn; RUST_LOG replaces that with env_logger-style
directives, e.g. RUST_LOG=debug or RUST_LOG=warn,gridcraft_engine=debug (a trailing *
matches a prefix: gridcraft*=debug). Runs with GRIDCRAFT_NO_PREFS set (no saved settings)
log to standard error only.
For agents: MCP, CLI and the control channel
claude mcp add gridcraft -- gridcraft-cli mcp # headless MCP server
gridcraft-cli mcp --connect 7979 # MCP bridged to a running window
gridcraft-cli eval '=XLOOKUP("b",{"a","b"},{1,2})' # → 2
gridcraft-cli run --sample budget --cmd 'home.bold={"range":"B4:F4"}' --out budget.xlsx
gridcraft-cli cat budget.xlsx --range B4:F15 # aligned text table
gridcraft-cli commands --search chart # every command and its params
The MCP server offers tools such as read_range, write_range, set_cell, evaluate_formula,
format_range, insert_chart, create_table, sort_range, filter and execute_command
(which reaches every one of GridCraft's commands). The desktop app's control channel adds real
pointer and keyboard input, dialogs and screenshots. See docs/mcp.md,
docs/cli.md and docs/control-protocol.md.
Architecture
GridCraft is an engine-first Cargo workspace with enforced layering (cargo xtask layers). The
egui frontend is a separate crate, so the UI can be swapped without touching the engine.
| Layer | Crates |
|---|---|
| L0 | core (addresses, values, errors, dates, input parsing) · numfmt (number format codes) |
| L1 | formula (lexer, parser, printer, reference adjustment) · functions (worksheet function library) |
| L2 | model (workbook, sheets, copy-on-write cells, styles, tables, charts…) · calc (dependency graph, evaluator, dynamic arrays) · xlsx (XLSX, CSV, plus XLSB and ODS data import) |
| L3 | chart (toolkit-free chart layout and rendering) |
| L5 | engine (session, commands, history, clipboard, fill, sort, filter, file I/O) |
| L6 | ui-egui (spreadsheet UI, control channel) · mcp (MCP server) |
| L7 | apps/gridcraft, apps/gridcraft-cli, apps/gridcraft-web |
- Contributor and agent rules (clean-room, asset policy, never-crash, quality gates):
AGENTS.md - Bundled assets: each one is listed with its licence in
ATTRIBUTION.md - Releases: signed macOS, Windows, Linux, BSD and web builds; see
docs/releasing.md
Roadmap
GridCraft is in alpha: the core workflow works end to end, but depth, fidelity and file
compatibility are still rough. It covers 89% of standard ribbon commands in our catalog
(docs/parity-checklist.md) and 513 standard worksheet functions
(docs/function-parity.md); this is a parity inventory, not a count of working implementations. Weighted by what spreadsheet users rely on, we
estimate it is about 50% ready for real work. Next up: XLSX fidelity on real-world files, very large
workbooks and multi-threaded recalc, chart depth, text in every script, and .xls import. Stage,
numbers and estimates are in ROADMAP.md; the ranked work list is docs/gaps.md.
Downloads
Download GridCraft from GitHub: the latest release has every build listed below, and all releases has earlier versions and their notes. <ver> in the file names is the version number, and SHA256SUMS.txt lists a checksum for every file.
Windows
| Build | Installer | Portable |
|---|---|---|
| x64 (64-bit Intel/AMD) | gridcraft-<ver>-windows-x64.msi |
gridcraft-<ver>-windows-x64-portable.zip |
| arm64 (Snapdragon and other ARM PCs) | gridcraft-<ver>-windows-arm64.msi |
gridcraft-<ver>-windows-arm64-portable.zip |
| x86 (32-bit) | gridcraft-<ver>-windows-x86.msi |
gridcraft-<ver>-windows-x86-portable.zip |
Installers and executables are code-signed. The MSI installer offers an optional desktop shortcut (unchecked on a new installation).
If the app doesn't open on Windows: the desktop app initializes only DirectX 12 by default.
Letting wgpu also create an OpenGL instance can crash some graphics drivers (AMD's
atio6axx.dll) before the window appears, so the app would flash in Task Manager and quit.
WGPU_BACKEND overrides the default for troubleshooting (for example dx12 or vulkan). In
PowerShell, from the folder containing the executable:
$env:WGPU_BACKEND = "vulkan"
& .\gridcraft.exe
Remove-Item Env:WGPU_BACKEND # restore the default for later launches
An explicit gl override can bring the driver crash back on affected systems, and vulkan can
bring back a crash in some Intel UHD Graphics drivers (igvk64.dll, #120). The macOS, Linux and
web backend defaults are unchanged.
If the app is slow on an older Windows PC, or DirectX 12 can't start: when DirectX 12 finds no
graphics card with a driver for it, it only offers the Windows-provided software renderer, which draws every
frame on the processor. In that case GridCraft uses OpenGL instead, without setting anything; if
the first renderer fails to start, it tries the other one once. The log file records the choice
(lines starting with graphics:). WGPU_BACKEND still overrides it (and then nothing else is
tried), e.g. $env:WGPU_BACKEND = "gl" or "dx12".
DirectX 12 shaders are compiled with FXC, which is part of Windows, so no dxcompiler.dll or
dxil.dll is needed, and a copy another program put on PATH can no longer stop the app at start
("Parent device is lost", #339). $env:WGPU_DX12_COMPILER = "dxc" (or "auto") selects wgpu's DXC
handling again for troubleshooting.
macOS
| Build | File | Notes |
|---|---|---|
| App, universal (Apple silicon + Intel) | gridcraft-<ver>-macos-universal.dmg |
Signed and notarized |
| Command-line tool, universal | gridcraft-cli-<ver>-macos-universal.zip |
Signed and notarized |
Linux
| Format | x86_64 | aarch64 (ARM64) | Notes |
|---|---|---|---|
| AppImage | gridcraft-<ver>-linux-x86_64.AppImage |
gridcraft-<ver>-linux-aarch64.AppImage |
Runs anywhere; updates itself with AppImageUpdate (.zsync files) |
| Flatpak | gridcraft-<ver>-linux-x86_64.flatpak |
gridcraft-<ver>-linux-aarch64.flatpak |
Sandboxed; flatpak install --user <file> |
| Debian/Ubuntu | gridcraft-<ver>-linux-x86_64.deb |
gridcraft-<ver>-linux-aarch64.deb |
|
| Fedora/RHEL/openSUSE | gridcraft-<ver>-linux-x86_64.rpm |
gridcraft-<ver>-linux-aarch64.rpm |
|
| Tarball | gridcraft-<ver>-linux-x86_64.tar.gz |
gridcraft-<ver>-linux-aarch64.tar.gz |
Unpack anywhere |
FreeBSD
| Build | File |
|---|---|
| x86_64 | gridcraft-<ver>-freebsd-x86_64.tar.gz |
Web (WebAssembly)
| Build | File | Notes |
|---|---|---|
| Static site | gridcraft-web-<ver>.zip |
Runs in a modern browser; host it on any static server |
The Crafting Apps
GridCraft is one of the Crafting Apps: free, open-source creative tools from the ArtCraft team, each written from scratch in Rust and each able to stand on its own.
| App | What it's for | Code | Learn more | |
|---|---|---|---|---|
 |
PhotoCraft | Image editing: layers, masks, type and real PSD files | GitHub | Website |
 |
VectorCraft | Vector illustration | GitHub | Website |
 |
FilmCraft | Video editing, color and sound | GitHub | Website |
 |
LightCraft | Photo library and raw development | GitHub | Website |
 |
PdfCraft | Reading, organizing and protecting PDFs | GitHub | Website |
 |
EffectCraft | Motion graphics and visual effects | GitHub | Website |
 |
DesignCraft | Page layout and publishing | GitHub | Website |
 |
GridCraft | Spreadsheets and data · you are here | GitHub | Website |
And ArtCraft itself, our AI image and video studio for artists who want real control.
Come make things with us
Our Discord is where artists of every kind hang out: people who paint, shoot, draw, cut film, set type, and people still figuring out what they like to make. Share what you're working on, ask for help, tell us what's broken, or tell us what you wish these tools could do. Whatever your medium and however long you've been at it, you're welcome here.
discord.gg/artcraft · getartcraft.com · The Crafting Apps · GridCraft
License and credits
GridCraft is dual-licensed under MIT or Apache-2.0, at your option. Copyright (c) 2026 ArtCraft Team and the GridCraft contributors. Required notices are in NOTICE.
Bundled fonts, icons, images and other assets keep their own open licenses; each one is listed with its author, source and license in ATTRIBUTION.md.
All UI icons are drawn in code and are original; the sample workbooks and every screenshot in this README were made with GridCraft itself. GridCraft bundles no fonts: it uses the fonts installed on your system.
The ArtCraft name, wordmark and logos in docs/brand/ are trademarks of the
ArtCraft Team and are not covered by this license. They may be used only unmodified, and only as
part of this repository and GridCraft, under docs/brand/LICENSE-brand.txt.
Forks and modified versions must remove them.
Made by the ArtCraft team and community.