Familiar spreadsheet work. A broader data workspace.
Work with cells and formulas, organize data, and keep analytical outputs in one place. Built in Rust, MythSheet is exploring inspectable AI assistance while keeping people in control.
Row 6 has a bank line with no ledger entry. Mark it for review?
Illustrative interface, not a screenshot. AI workflows and compatibility are still being validated.
A bank export, reconciled.
What the development build does today, from file to a result you can check.
- 01
Open, safely
The original file stays protected. Work happens on a copy, with a warning for unsaved changes and a check if the file changes on disk.
- 02
Paste the export
Pasting keeps types in check: leading zeros stay as text, and a batch of edits is undone in one step.
- 03
Reconcile
Formulas and a reconciliation worksheet compare bank and ledger, with status and validity checks per row.
- 04
Check the result
A read-only sorted or filtered view and a basic dashboard from an explicit range, so you can see what changed.
Working in development builds
Verified locally. Not a public release.
- Editable cells, formula bar, sheet navigation, range selection and the basic shortcuts
- Type-guarded copy and paste, leading zeros kept as text, one undo for several batch operations
- Basic number and percent formats and bold (not a full formatting system yet)
- Find, plus read-only sorted and filtered views (they do not reorder the sheet itself)
- A basic dashboard from an explicit data range and field mapping
- Worksheets for reconciliation, manual cash planning and weekly project reports, each with its own status and some validity checks (not accounting software)
- Original-file protection, save as copy, unsaved-changes prompt and external-change check
- Manual recovery checkpoints (limited: not autosave or crash-proof recovery)
- Light and dark themes, collapsible icon sidebar, grouped settings with Apply, Cancel and Reset
- An optional recent-files list that stores only limited local paths and never opens files by itself
In progress
- Safe text replace: literal, case-sensitive replace inside a chosen range, one undo and redo for the whole change, preview tied to the document version. Numbers, formulas and blanks are skipped, and a result that starts with = stays text. Sheets with merged cells are refused for now.
- Windows builds: not yet verified natively. Today's builds run on Linux.
- AI with your own model key: experimental, see below.
Planned
- Real paged print preview and PDF export, with orientation, margins, scaling, repeated headers, headers and footers
- System print dialog, checked against real output
- AI that sets up layout through structured tools, previews it and asks before printing
- Fuller data validation, autofill, frozen rows and columns, conditional formats, charts and pivot summaries
- Chinese input methods, native assistive technology, large files and crash recovery, tested one by one
AI, your key, your data
Local first, and clear about what leaves.
The direction is bring-your-own-key: you connect a model API, and the AI works through tools to read and analyse data and propose changes. Changes apply only after you approve them.
Local first does not mean nothing ever leaves: when you use an external model, the data in each request goes to the provider you configured. We will document exactly what each request contains before release.
Today this is experimental. Keys live only in memory while the app runs (no keychain yet), and settings files never store keys, sheet contents, proposals or approvals. Full end-to-end behaviour with real models has not been verified, and AI writes through MCP stay blocked until a trusted approval channel exists.
Formulas
Common formulas, tested. Not everything.
The formula engine is built on IronCalc. Common maths, conditional aggregates, lookups, dates, finance and some dynamic array formulas are implemented and tested with samples.
Some argument combinations are not supported or not yet verified, for example certain TEXTJOIN array uses. MythSheet is not a full Excel replacement, and compatibility is checked function by function.
The honest answers.
Can I use it today?
Which files does it work with?
Which platforms?
Does my data leave my computer?
Is it a replacement for Excel?
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In development · not yet released