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Limitations

Known gaps, each of them deliberate rather than pending:

  • INDIRECT is unsupported. A reference computed at evaluation time cannot be seen by the static dependency extractor, so the recalculation order would be wrong -- see Topological recalc.

  • LAMBDA and its higher-order helpers (MAP, REDUCE, BYROW, and the rest) are unsupported; LET is supported. Dynamic-array results are packed into their origin cell rather than spilling into neighbours.

  • xlsx export of formulas is EXCEL mode only. PYTHON and HYBRID syntax (**, list comprehensions, py.*) is not strict Excel, so those modes export values.

  • 3D range refs (Sheet1:Sheet3!A1:B2) are unsupported and return nan. Workaround: expand them manually with +.

  • Cross-sheet ranges (Sheet1!A1:Sheet2!B5) are rejected at parse time. Excel does not support them either.

  • xlsx dates and styles are neither read nor written; date serials arrive as floats.

The Excel function coverage audit tracks the function library itself against Microsoft's documented set, including which absences are architectural and which are merely unimplemented.

For what the desktop frontend does not do yet -- a separate question from engine limitations -- see Desktop app.