Online Tool Store
Date Format Standardizer
Paste a list of dates in mixed formats and convert them all to a single consistent format, with unrecognized dates flagged. Runs entirely in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
How the date format standardizer works
- Paste one or more dates, one per line - a sample loads automatically.
- Set how ambiguous slash-separated dates should be interpreted, and pick your desired output format.
- Copy the standardized list, ready to paste back into a spreadsheet or database import.
FAQ
What date formats can this tool parse?
ISO format (YYYY-MM-DD), slash or dash separated dates (MM/DD/YYYY or DD-MM-YYYY), and written-out dates like "December 25, 2025".
Why does the tool ask whether ambiguous dates are MM/DD or DD/MM?
A date like 03/04/2026 is genuinely ambiguous - it could mean March 4th or April 3rd depending on regional convention. Setting this option tells the parser how to interpret slash-separated dates consistently.
What happens if a date can't be parsed?
It's marked as "[unrecognized: ...]" in the output so you can spot and fix it manually, rather than silently guessing.
Can I convert a whole column of dates from a spreadsheet?
Yes - paste one date per line (works well when pasted directly from a spreadsheet column) and every line is converted independently.
How we compare
| Feature | Online Tool Store | Spreadsheet formula | Manual retyping |
|---|---|---|---|
| Handles multiple mixed formats at once | ✓ | ✗ | ✗ |
| Flags unrecognized dates | ✓ | ✗ | ✗ |
| No formula syntax to learn | ✓ | ✗ | ✓ |
Useful for cleaning up a data import where dates were entered in inconsistent formats before loading into a system that expects ISO dates.