Clean Data Clean messy data in the active sheet or a specified range. Environment If running inside Excel (Office Add-in / Office JS): Use Office JS directly ( Excel.run(async (context) => {...}) ). Read via range.values , write helper-column formulas via range.formulas = [["=TRIM(A2)"]] . The in-place vs helper-column decision still applies. If operating on a standalone .xlsx file: Use Python/openpyxl. Workflow Step 1: Scope If a range is given (e.g. A1:F200 ), use it Otherwise use the full used range of the active sheet Profile each column: detect its dominant type (text / number / date) and identify outliers Step 2: Detect issues Issue What to look for Whitespace leading/trailing spaces, double spaces Casing inconsistent casing in categorical columns ( usa / USA / Usa ) Number-as-text numeric values stored as text; stray $ , , , % in number cells Dates mixed formats in the same column ( 3/8/26 , 2026-03-08 , March 8 2026 ) Duplicates exact-duplicate rows and near-duplicates (case/whitespace differences) Blanks empty cells in otherwise-populated columns Mixed types a column that's 98% numbers but has 3 text entries Encoding mojibake ( é , ’ ), non-printing characters Errors

REF!

,

N/A

,

VALUE!

,

DIV/0!

Step 3: Propose fixes Show a summary table before changing anything: Column Issue Count Proposed Fix Step 4: Apply Prefer formulas over hardcoded cleaned values — where the cleaned output can be expressed as a formula (e.g. =TRIM(A2) , =VALUE(SUBSTITUTE(B2,"$","")) , =UPPER(C2) , =DATEVALUE(D2) ), write the formula in an adjacent helper column rather than computing the result in Python and overwriting the original. This keeps the transformation transparent and auditable. Only overwrite in place with computed values when the user explicitly asks for it, or when no sensible formula equivalent exists (e.g. encoding/mojibake repair) For destructive operations (removing duplicates, filling blanks, overwriting originals), confirm with the user first After each category of fix (whitespace → casing → number conversion → dates → dedup), show the user a sample of what changed and get confirmation before moving to the next category Report a before/after summary of what changed