Spreadsheet analysis
Ask questions about an Excel or CSV file, have unusual entries found and cells filled with checked formulas, and recalculate the result in Excel.
You have a spreadsheet and need an overview quickly: how are the hours distributed, what stands out, what is missing? Custodos reads Excel and CSV files, answers questions about them and, on request, writes formulas directly into your Excel file. Formatting, other sheets and charts are kept.
The example: Lea Keller analyses the timesheet for the third quarter. The file "Timesheet Q3 2026.xlsx" has two sheets: "Hours" with date, employee, client, activity and hours, and "Rates" with the hourly rates per activity from the Fee Schedule 2026.
Workflow
Prepare the spreadsheet
The tidier the spreadsheet, the better the answers:
- one header row with unambiguous column names,
- one table per sheet, without subtotals in the middle of the data,
- no merged cells in the header row,
- columns not needed for the question removed beforehand, especially payroll or personal data.
Attach the file
In the message box, click Add and Attach file, or drag the file into the chat. The file's card shows how many characters Custodos has read. In Pseudonymise mode, detected employee names go to the model as placeholders and are put back in the reply.
Ask questions
Attached is our timesheet for the third quarter of 2026. Please answer:
- How many hours are there for each client? As a table, sorted in descending order, with the number of entries per client.
- Which entries stand out, for example more than 10 hours on one day, a missing client or an activity that does not appear in the "Rates" sheet? Give the row number for each.
Do not invent values. If something in the spreadsheet is ambiguous, say so.
The count of entries per client makes checking easier: if it matches Excel, the total usually does too.
Check the answer
Check the most important figures in Excel, for example with a pivot table or a sum formula per client. Open the rows the reply names and see whether they really stand out. Where figures differ, Excel is right.
Have formulas written into the file
Let Excel do the maths instead of copying figures from the chat:
In the sheet "Hours", fill column F with the fee: heading "Fee" in F1, and from F2 a formula for hours times the hourly rate of the activity from the sheet "Rates". Change nothing else in the file.
While it works, the answer shows Editing Excel file…. Before writing, Custodos checks every formula: whether the sheets it names exist, whether a cell refers to itself, whether the functions are known and the brackets complete. Afterwards a new file appears below the answer for download, for example "Timesheet-Q3-2026-bearbeitet.xlsx". Your original file stays unchanged.
Check in Excel
Excel recalculates all formulas when the file is opened. Then check:
- recalculate three rows by hand, including the last row of the table,
- whether error values such as #N/A appear, for instance for an activity missing from the "Rates" sheet,
- whether the formula uses the right columns.
The check before writing prevents broken formulas, but not a formula that is valid and still calculates the wrong thing.
More options
- Change values or add rows. "In the Rates sheet, set the hourly rate for bookkeeping to the value in the Fee Schedule 2026." Custodos can set cells, clear a range and append rows at the bottom.
- A new analysis as a separate file. "Create an Excel file with an overview of hours per client and month, totals as formulas." This creates a new workbook, for example from a CSV file.
- Charts. Custodos does not insert charts into an Excel file, but existing ones are kept. Ask which chart suits your question and which range to select for it, or have a PowerPoint presentation created with a bar, line or pie chart.
What makes this workflow safe
| Feature | What it does here |
|---|---|
| New file | The original stays unchanged, so you can compare before and after. |
| Formula check | Missing sheets, circular references, unknown functions and unclosed brackets are caught before anything is written to the file. |
| Recalculation on opening | Excel calculates itself instead of taking values from the chat. |
| Pseudonymisation | Detected names, email addresses and account numbers go to the model as placeholders. The edited file contains the real values again. |
Limits
Best practices
- Treat figures from the chat as an overview and figures from Excel as the result.
- Describe formulas in words; the model translates them into Excel functions.
- Name the sheet and column so that the right place is changed.
- Write "Change nothing else" when only one area should be affected.
- Work on a copy of the file if you later carry formulas over into the original.
Frequently asked questions
The model adds up the values from the text it read, and can make mistakes, especially with many rows. The total in Excel is what counts. Have important totals written into the file as formulas.
No, because that would shift references in formulas and charts. Custodos can append rows at the bottom or fill empty cells. Insert a row in the middle of the table in Excel.
Not directly. Custodos reads the CSV file and, on request, creates a new Excel file with the same data, formulas and a header row.
No. Custodos only changes the cells you ask for. Formatting, column widths, other sheets, pivot tables and charts stay as they were.
Next steps
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