A CSV is plain text. Excel guesses what each cell means when it opens the file, and saving afterwards writes the guess back. The result: files that look fine but import wrongly somewhere else.
Leading zeros disappear
A code such as 00123 is read as the number 123. Zip codes, SKUs and product codes are common victims. Fix: import the column as Text, or use a tool that writes the file as .xlsx with the value kept as text.
Long IDs lose digits
Excel stores numbers with about 15 significant digits. A 20-digit ID is rounded and shown as 1.23457E+19. Once saved, the original digits are gone for good. Always check long numeric IDs before and after.
CSV ID Keeper keeps IDs exactly as written and reports what Excel would have damaged. Product page
Values that look like numbers or dates
1E5 becomes 100000. 3-4 can become 3 April. Gene names, part numbers and ranges are often damaged this way.
Day/month ambiguity
04/05/2026 is 4 May in some countries and 5 April in others. A file with only ambiguous dates cannot be fixed automatically. Check whether any date has a day above 12, and agree on one format with whoever receives the file.
CSV Date Fit flags ambiguous, impossible and two-digit dates. Product page
Delimiters and encoding
Some systems expect commas, others semicolons or tabs. If accented characters show as odd symbols, the encoding (UTF-8 versus a legacy code page) is wrong. Excel on one computer may use a different delimiter than on another.
CSV Dialect Switch detects delimiter and encoding before saving. Product page
Hidden characters
Non-breaking spaces, zero-width characters and tabs make two codes that look identical fail to match in a lookup. Search for them when a lookup should work and does not.
CSV Ghost Chars shows hidden characters and reports every change. Product page
Repeat the same cleanup
If you receive the same export every week, write the steps down once: column order, formats, checks. Doing it by hand each time is how mistakes return.
Offline browser tools that handle these cases: CSV ID Keeper, CSV Date Fit, CSV Dialect Switch, CSV Ghost Chars and CSV Profile Runner.
They run offline in the browser, so your files are not uploaded anywhere. All products and prices: https://asecrier.gumroad.com
A PDF version of this checklist is on Scribd.
