What is this date normalizer?
A free, browser-based tool that converts a list of dates written in mixed formats into one consistent format. Paste one date per line — it understands YYYY-MM-DD, YYYY/MM/DD, MM/DD/YYYY, DD/MM/YYYY, DD-MM-YYYY, YYYY年MM月DD日, and ISO datetimes — and rewrites them all to the output format you choose (YYYY-MM-DD by default). Rows it can't parse are flagged in red so nothing slips through silently. Everything runs locally in your browser, so your data is never uploaded.
How to use it
- Paste your dates (one per line) into the box on the left.
- Choose the output format, and toggle 'Day first (DD/MM)' if your numeric dates put the day before the month.
- Read the normalized list on the right — unparseable rows are highlighted in red — then copy or download the result.
Common use cases
- Cleaning a date column exported from a CRM or spreadsheet before importing it elsewhere.
- Standardizing dates collected from multiple forms or regions into a single format.
- Spotting impossible or malformed dates that would break a later import.