gridcraft/docs/file-format-parity.md

File-format parity

Last reviewed: 2026-10-11 · Last updated: 2026-10-19 · Change: minor (XLSX column declarations share a per-sheet expansion-work limit; pictures in XLSX headers and footers are kept on save; legacy XLSX INDEX/MATCH formulas stay scalar on save; XLSX text keeps carriage returns on save and reopen; .xls dialog sheets are skipped instead of read as worksheets; .xls import reads each sheet's display options from WINDOW2: right-to-left, gridlines, headings, zeros, formulas; XLSX text boxes and shapes keep their paragraphs' right-to-left direction on save; CSV/TSV/TXT can open with every field kept as text via file.open {csvAsText}; formulas over Excel's 8,192 characters, and % or call chains past the nesting limit, are parse errors instead of stack overflows when a file is opened; XLSX PivotTables read and write rowGrandTotals/colGrandTotals the way Excel does, so a table saved with only one grand total opens with the right one; HTML export keeps right-to-left) · Target: Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4

Every format Excel opens or saves, with GridCraft's read and write support, fidelity and tests. Part of target-app-parity.md. File formats: ~50% ready, 80–120 h (estimated).

Excel's list comes from Microsoft's public "File formats that are supported in Excel" documentation (the Office bundle is off limits under this repo's clean-room rule). GridCraft's support comes from crates/engine/src/io.rs (FileKind), crates/xlsx/src and the tests in crates/xlsx/src/tests/ (round-trip, fixtures, malformed input, CSV, ODS, XLSB, XLS, PivotTables).

Legacy scalar INDEX(range, MATCH(...)) formulas remain ordinary formulas on save, including when shared formulas are expanded during import (array_export.rs, #1505).

Workbook formats

XLSX column declarations are limited to 1,000,000 expanded column assignments per worksheet, including repeated overlaps across <cols> blocks. Spans are clipped to the grid and records that would be skipped as defaults are excluded before charging the limit. Excess work returns the existing file-too-large error; accepted overlaps retain their existing last-wins behavior (#1022).

Ink created with Draw is written as standard, unfilled DrawingML polylines, without visible point captions or private metadata. Supported numeric polylines reopen as editable ink, retaining points, colour, integer width and anchor. Curves, filled paths, transforms and unsupported line styles are not interpreted as ink. This does not implement Office InkML or fix inserted icons (#551). Command and package tests cover repeated saves and unrelated cell edits; external Excel rendering and repair-free opening remain unverified.

Format	Excel	GridCraft read	GridCraft write	Fidelity / notes	Tests
.xlsx Excel Workbook (transitional)	R/W, native	yes	yes	Cells, shared/array/dynamic formulas, styles, themes, merges, CF, validation, tables, comments and notes, hyperlinks, names, freeze panes, outline, print settings, pictures, shapes, charts (simplified, see chart-parity.md), sparklines, PivotTables (caches and tables), protection, calc settings. Kept unchanged on save (pass-through, passthrough.rs): custom document properties, ribbon customisation and add-in task panes, custom XML, links to external workbooks (never followed or refreshed), data connections, sheet query tables, printer settings (#324), form controls, ActiveX controls, OLE objects and sheet backgrounds (with their VML shapes), pictures in headers and footers (&G, #1257: their VML drawing and images are written back unchanged; they are not shown, and can't be inserted), and chart sheets (#727: the sheet, drawing, chart, style and colour parts are written back unchanged in their place, and left out when a sheet they plot was deleted or renamed or a worksheet took their name; they can't be edited or created); dropped when their sheet is deleted or their parts point at content GridCraft rewrites. Not preserved: slicers and slicer caches, timelines, data model, query tables attached to tables, sheet and workbook extLst entries we don't model, chart details; Strict Open XML files keep nothing. Never checked in Excel across a corpus: repair prompts unknown. 100 MB files fail (#175)	roundtrip.rs, fixtures.rs, malformed.rs, pivot_tests.rs
.xlsx Excel Workbook (transitional)	R/W, native	yes	yes	Cells, shared/array/dynamic formulas, styles, themes, merges, CF, validation, tables, notes (with their shown/hidden state) and threaded comments with replies, resolved state and timestamps (threadedComments and persons parts, #300), hyperlinks, names, freeze panes, outline, print settings, pictures, shapes, charts (simplified, see chart-parity.md), sparklines, PivotTables (caches and tables), protection, calc settings. Not preserved: unmodelled parts and extensions (form controls, slicer caches, timelines, external links, OLE objects, custom XML, data model, query tables, chart details). Never checked in Excel across a corpus: repair prompts unknown. 100 MB files fail (#175)	roundtrip.rs, fixtures.rs, malformed.rs, pivot_tests.rs
.xlsx Excel Workbook (transitional)	R/W, native	yes	yes	Cells, shared/array/dynamic formulas, styles, themes, merges, CF, validation, tables, comments and notes, hyperlinks, names, freeze panes, outline, print settings, pictures, shapes, charts (simplified, see chart-parity.md), sparklines, PivotTables (caches and tables), protection, Allow Edit Ranges (protectedRanges with their password hashes, #307), calc settings. Not preserved: unmodelled parts and extensions (form controls, slicer caches, timelines, external links, OLE objects, custom XML, data model, query tables, chart details). Never checked in Excel across a corpus: repair prompts unknown. 100 MB files fail (#175)	roundtrip.rs, fixtures.rs, malformed.rs, pivot_tests.rs
.xlsx Strict Open XML	R/W	yes	no (writes transitional)	Excel also saves transitional by default	fixtures
.xlsm Macro-Enabled Workbook	R/W	yes	yes, macros kept, not run	The VBA project is kept byte-for-byte and written back only into .xlsm/.xltm (#6); macros never run. Saved with the macro-enabled workbook content type	roundtrip.rs (vba_project_roundtrip, package_kind_sets_workbook_content_type), engine io.rs (macros_are_saved_only_into_xlsm)
.xltx / .xltm templates	R/W	yes	partial	Saved with the template (and macro-enabled template) content type, chosen by extension; .xltm keeps a VBA project, .xltx drops it; "new from template" behaviour missing	roundtrip.rs (package_kind_sets_workbook_content_type), engine io.rs
.xlsb Binary Workbook	R/W	values only (#101)	no	Names, visibility, numbers, text, booleans, errors, merges, cached formula results; no formulas, formatting, charts, names	xlsb_tests.rs
.xls Excel 97-2003 (BIFF8)	R/W	yes, partial (#121)	no (Save As .xlsx)	Clean-room from [MS-CFB] and [MS-XLS]. Read: worksheets and visibility, shared strings, numbers, text, booleans, errors, formulas (text for the common tokens, shared and array formulas, 3-D refs, names, newer functions called by name) with cached results, number formats (dates display as dates), 1904 date system, merges, column widths, row heights, defined names, print area and titles, calculation settings (mode, iteration with its maximum iterations and change, precision as displayed), sheet display options (right-to-left, gridlines, headings, zero values, formulas; a truncated WINDOW2 is ignored). Not read: fonts, fills, borders, alignment, charts, pictures, comments, CF, validation, hyperlinks, freeze panes, external links (formula kept as its value). Chart and macro sheets skipped with a warning; encrypted (FILEPASS) and BIFF5 (Excel 5.0/95) files refused with a message. Opens as a new unsaved workbook. Unverified on a real-world corpus	xls_tests.rs
.xlt Excel 97-2003 template	R/W	yes (read as .xls)	no		—
.xlam / .xla add-ins	R/W	no	no	VBA; out of scope	—
.xml XML Spreadsheet 2003	R/W	no	no	Simple to support	—
.ods OpenDocument Spreadsheet	R/W	values only (#100)	no	Sheets, values, dates, merges, repeated cells, cached formula results; no formulas, formatting, charts; encrypted ODS refused	ods_tests.rs
Password-encrypted workbooks (Agile/Standard encryption)	R	yes (#11): asks for the password on open; Agile (AES-128/192/256, SHA-1/256/384/512) and Standard (AES, SHA-1)	no (opens with no save path; Save As writes it without the password)	Clean-room from [MS-OFFCRYPTO] on the CFB reader. RC4, Extensible and certificate-only encryption refused with a message. Data-integrity HMAC not checked	crypto/tests.rs, encrypted_tests.rs
.xlw Excel 4.0 workbook, .wk*, .dbf	open only (some)	no	no	Rare	—

Text and data formats

Format	Excel	GridCraft read	GridCraft write	Notes
.csv UTF-8 / Windows / Mac / MS-DOS	R/W	yes (UTF-8 and UTF-16 BOMs, UTF-8, Windows-1252 fallback; delimiter detection)	yes (UTF-8 without BOM, CRLF; a file opened as CSV is saved with the separator it was read with, so a ; file stays ;; otherwise ,)	Excel writes the displayed values; we write raw values. No encoding choice on save. Re-import of a single-column export splits text (#127) A used range that would write more than 512 MiB (two far-apart cells span the whole rectangle) is refused with an error instead of being expanded (#528).
.txt tab-delimited, Unicode text	R/W	yes (.txt, .tsv, .tab)	yes	Text Import Wizard options partly via Text to Columns
.csv UTF-8 / Windows / Mac / MS-DOS	R/W	yes (UTF-8 and UTF-16 BOMs, UTF-8, Windows-1252 fallback; delimiter detection)	yes (UTF-8 without BOM, CRLF)	Writes the displayed values like Excel (number formats applied, formula results, never column-width #####). No encoding choice on save. Re-import of a single-column export splits text (#127) A used range that would write more than 512 MiB (two far-apart cells span the whole rectangle) is refused with an error instead of being expanded (#528).
.txt tab-delimited, Unicode text	R/W	yes (.txt, .tsv, .tab)	yes (displayed values)	Text Import Wizard options partly via Text to Columns
.prn formatted text (space-delimited)	R/W	no	no
.dif, .slk (SYLK)	R/W	no	no	Small, legacy
.htm / .html web page	R/W (Windows)	yes, via Get Data ▸ From HTML	yes (one sheet as a table; a used range taller than 100,001 rows fails with an error instead of being cut short)	Formatting not exported
.mht / .mhtml single-file web page	R/W (Windows)	no	no
.json	via Power Query	GridCraft's own workbook JSON (debug) and JSON import	GridCraft JSON	Not Power Query's JSON shaping; notes and hyperlinks break export (#126)
.xml with XML maps	Developer ▸ Import/Export	no	no

Export and print

Format	Excel	GridCraft	Notes
PDF	Save As / Export	yes (own PDF 1.7 writer)	Only the 14 standard PDF fonts, no embedding: non-Latin text (CJK, Arabic, Devanagari, Thai) does not export; web build exports without a file prompt (#141)
XPS	Windows	no	Low priority
Print	yes	yes (via PDF, system dialog on desktop; PR #143 for web)
Images of ranges/charts (Copy as Picture)	yes	chart raster in crates/chart	No range-to-image command

Import sources (Get & Transform)

Excel's Get Data reaches files (Excel, CSV, XML, JSON, PDF, Parquet, folders), databases (SQL Server, Access, ODBC, …), web pages, SharePoint and online services, through Power Query. GridCraft imports CSV/TSV, JSON and HTML tables only, with no query editor, no connections and no refresh. Counted under features (Get & Transform, ~10% ready), not here.

Work (76–114 h)

Work	Hours
Real-world XLSX corpus run (craftrules test-corpora standard), and confirm Excel opens our output with no repair prompt (owner runs Excel)	15–25
Preserve the rest of the unmodelled XLSX content (slicers, timelines, data model, table query tables, extLst entries); pass-through landed for the rest (#330)	6–10
Streaming XLSX reader for very large files (#175), part-size limits that degrade instead of failing	10–15
Legacy .xls (BIFF8): styles (fonts, fills, borders, alignment), comments, CF, validation, pictures and charts on import; corpus run; then write	10–15
Encrypted workbooks: save with password (#11)	4–6
XLSB and ODS: formulas and formatting on import; then write	10–15
CSV/text: encoding choice, .prn, .dif, .slk, XML Spreadsheet 2003	4–7
PDF: embed subsetted system fonts so every script exports	(counted in localization script work)

Revision history

Date	Change	Summary
2026-10-19	minor	.xls import skips dialog sheets (WsBool fDialog), which share the worksheet BOF type and were read as empty worksheets
2026-10-19	minor	.xls import reads WINDOW2: right-to-left sheets (common in older Arabic and Hebrew files) open right-to-left, and hidden gridlines, headings and zero values and Show Formulas carry over
2026-10-19	trivial	XLSX text boxes and shapes keep right-to-left paragraph direction (a:pPr rtl, ECMA-376 Part 1 §21.1.2.2.7): read from the first paragraph and written on every paragraph; output without it is unchanged
2026-10-18	trivial	file.open {csvAsText: true} keeps every CSV/TSV/TXT field as the text the file holds, so identifiers (GTINs, SKUs, ZIP codes) keep their digits and leading zeros (#1808; a preference and a CLI flag are separate work)
2026-10-18	trivial	XLSX PivotTables: rowGrandTotals is the Grand Total row and colGrandTotals the Grand Total column. Both were read and written the other way round, which a GridCraft round trip hid, so an Excel file with only one grand total opened showing the other
2026-10-19	minor	HTML (Save as Web Page and clipboard) marks right-to-left sheets and right-to-left cell text with dir
2026-10-16	trivial	XLSX: pictures in headers and footers (&G, the VML drawing <legacyDrawingHF> names and its images) are kept on save; they are still not shown (#1257)
2026-10-16	minor	XLSX column imports refuse more than 1,000,000 cumulative expanded assignments per sheet before expanding the next span; repeated overlaps cannot bypass the work limit (#1022)
2026-10-14	trivial	Formula parser: text longer than Excel's 8,192 characters, and postfix chains (1%%%…, f(1)(1)…) past the 256-level nesting limit, are parse errors (the cell keeps its formula text and cached value) instead of trees deep enough to overflow the stack when a hostile file is opened, saved or dropped
2026-10-15	minor	XLSX text preserves CR and CRLF across save/reopen; shared strings use _x000D_ and other XML text uses &#13; (#1488)
2026-10-15	minor	XLSX save keeps legacy INDEX/MATCH formulas scalar instead of marking them as dynamic arrays (#1505)
2026-10-12	trivial	XLSX chart sheets are kept on save (#727)
2026-10-12	trivial	CSV and TSV export is capped at 512 MiB and refuses a larger used range with an error (#528)
2026-10-12	minor	.xls import reads the calculation settings (CalcMode, CalcIter, CalcCount, CalcDelta, CalcPrecision), so circular models calculate instead of showing #CIRC! (#724)
2026-10-12	minor	Ink paths and editing survive XLSX save/reopen; strict polyline import and malformed-input controls
2026-10-12	minor	.xls import: the other cells of an array formula ({=FREQUENCY(...)}, {=TREND(...)}) drop their cached results, as .xlsx import does, so the formula fills its range on recalculation instead of showing #SPILL! against its own old values; 79 fewer mismatching formulas and 16 fewer round-trip differences over 4,224 real-world files
2026-10-12	minor	macOS: the app bundle declares .xlsb and .ods, so Finder's Open With offers GridCraft for them, as Linux and Windows already did (#321)
2026-10-12	minor	CSV: saving a file opened as CSV keeps its detected separator (; files were rewritten with ,)
2026-10-11	minor	XLSX: cell/shared/array formulas read through the file→model conversion (_xlpm. LET/LAMBDA parameter prefixes stripped); table column names keep line breaks; table names may start with \
2026-10-11	minor	CSV/TSV export writes displayed values (number formats applied, no #####); .xltx, .xltm and .xlsm saved with their own workbook content types
2026-10-11	minor	Table AutoFilter criteria are read and written (they were dropped, leaving only the filter button), and iconFilter criteria are kept on table and sheet AutoFilters
2026-10-11	minor	Password-encrypted workbooks open with their password (Agile and Standard encryption, #11)
2026-10-11	minor	.xls (BIFF8) import: values, formulas, number formats, merges, sizes, names (#121)
2026-10-11	minor	XLSX pass-through: custom XML, external links, connections, query tables, printer settings, form/ActiveX controls, OLE objects, sheet backgrounds kept on save (#330, #324)
2026-10-11	minor	XLSX: threaded comments and persons parts written (they came back as notes before); note visibility read from VML (#300)
2026-10-11	minor	XLSX: Allow Edit Ranges (protectedRanges) read and written with their password hashes (#307)
2026-10-10	minor	Encrypted and .xls files are now recognised and refused with a message (#17)
2026-10-10	major	Created: every Excel format with our read/write support; XLSB and ODS values-only imports recorded; .xls, encryption and large files flagged as beta gates