CSV to Excel without losing leading zeros, long numbers or plus signs
In short: Scans every column for values Excel changes when it opens a CSV (leading zeros, numbers over 15 digits, 1-2 read as a date, 1E5, a leading +, =, TRUE/FALSE, 1,234) and writes a real .xlsx with those columns stored as text, or every column. Bold, frozen header row; nothing uploaded. Limit: One sheet per file; Excel's limit of 1,048,576 rows applies, and cells over 32,767 characters are cut.
Upload the CSV and the tool lists the columns Excel would change on opening it, such as zip codes losing their leading zero or 16-digit IDs being rounded, then writes an .xlsx with those columns stored as text. Open the .xlsx instead of the CSV and every value is exactly as it was in the file.
Price: this tool is free. Checking a whole email list is from $9/mo, and the first 100 checks are free with Google, no card. See pricing
Sample result
6 columns Excel would change: zip codes, IDs and phones lose zeros, order numbers get rounded.
- Cells at risk
- 15
- Columns
- 6 of 7
- Output
- .xlsx, frozen header
What this means for you
Open the .xlsx instead of the CSV; those columns are stored as text, so 02108 stays 02108.
- Leading zeros kept
- 16+ digit IDs kept
- No dates from 1-2
- Plain numbers stay numbers
- Excel
- Leading zeros
- CSV
By SimpleVerifier Team · Last updated · Runs in your browser; nothing you paste is sent to us
Also in: Português (Brasil) · Español
How do I check the email addresses in the sheet?
- Keep the original CSV, or download the .xlsx.
- Upload either at /verify. Every address gets a live mailbox check, and valid, risky and invalid download as separate files. The first 100 email checks are free with a Google sign-in, no card.
- Use the valid file for the import or campaign.
How do I convert a CSV to Excel and keep the leading zeros?
- Paste the CSV or upload it (up to 25 MB). Comma, semicolon and tab files are read.
- Press Check and convert and read which columns Excel would change and how.
- Choose to store only those columns as text (plain numbers elsewhere stay numbers) or every column.
- Download the .xlsx and open it in Excel, Numbers or Google Sheets.
Example
- You enter
- A 3-row CSV with email, zip, phone, customer_id, order_ref, size and notes columns, including
02108,+447911123456,000417, a 16-digit order reference,1-2and=tidy up. - You get
- 6 columns Excel would change on open, 15 cells: zip and customer_id would lose leading zeros, phone its zeros and plus sign, order_ref would be rounded, size read as dates, notes read as a formula and a TRUE. The .xlsx stores those columns as text, so every value opens exactly as written.
- Limits
- Runs in your browser with no row cap; an uploaded file can be up to 25 MB.
Why does Excel remove leading zeros from a CSV?
A CSV has no types: every value is text. When Excel opens one by double-click it guesses, and anything that looks like a number becomes a number, so 02108 is stored as 2108, +447911123456 loses its plus, a 16-digit order ID is rounded to 15 significant digits (4111111111111111 becomes 4111111111111110) and 1-2 becomes 2 January. Saving the file again writes the changed values back, so the damage is permanent.
An .xlsx records each cell's type. Cells written as text are never converted, so the file opens the same in every copy of Excel, in Numbers and in Google Sheets, with no import wizard. That's what this tool writes.
What does Excel change, and what does the tool check for?
Leading zeros (00742), numbers longer than 15 digits, values that read as dates (1-2, 3/4, 2024-03, 5-Jan), scientific notation (1E5), a leading plus on digits, values starting with =, @, or + or - before text (read as formulas), TRUE and FALSE, and thousands separators or a currency sign (1,234, $40). Each column with any of these is listed with an example and a count.
The other fixes Microsoft documents are an import step every time (Data, From Text/CSV, set the columns to Text) or, in current Microsoft 365, unticking Remove leading zeros under File, Options, Data, Automatic Data Conversion. Both work on your machine only; the .xlsx works for whoever you send it to.
Is this better than the Excel import wizard?
| This tool (.xlsx) | Data, From Text/CSV | Double-click the CSV | |
|---|---|---|---|
| Leading zeros | Kept | Kept if you set the column to Text | Dropped |
| 16+ digit IDs | Kept | Kept if set to Text | Rounded |
| 1-2, 3/4 | Kept | Kept if set to Text | Turned into dates |
| Works for the next person | Yes, types are in the file | No, they repeat the steps | No |
Who uses this tool, and for what?
- Marketing ops
- Send a contact list with zip codes and phone numbers to a colleague who will open it in Excel.
- E-commerce
- Open an order export with long order and tracking numbers without Excel rounding them.
- Finance and ops
- Keep account numbers, SKUs and part codes with leading zeros intact.
What can’t this tool tell you?
- One sheet per file; Excel's limit of 1,048,576 rows applies, and cells over 32,767 characters are cut.
- Dates are kept as text, not converted to Excel dates.
- The check covers the conversions listed above, not every regional setting Excel has.
- It keeps your values intact; it doesn't check whether the email addresses in them work. That needs a mailbox check.
Common questions
- Can I do calculations on the text columns?
- Not directly; they're text on purpose. Keep the default, which leaves plain number columns such as quantity or revenue as numbers.
- My file already lost its zeros. Can it put them back?
- Not automatically, since the zeros aren't in the file any more. For zip codes, find and replace with the regex
^(\d{4})$and0$1restores the zero on four-digit values. - Does it convert Excel to CSV too?
- No. Save As CSV UTF-8 in Excel does that; if the result shows é instead of é, use the CSV encoding fixer.
- Is my file uploaded?
- No. The workbook is built in your browser.
Sources
A tidy list can still be full of dead addresses.
Extracting, deduplicating and syntax checks all work on the text of an address. None of them can tell whether the mailbox exists. Only the server that hosts it can answer that, through an SMTP check, and that is what the paid product does.
- Upload the cleaned file as it is: CSVs up to 100,000 rows
- A real SMTP mailbox check on every row, with catch-all detection
- Small list? Starter at $9/mo covers 2,500 emails a month, cancel anytime
Plans from $9 a month, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.