Duplicate Date Finder

Paste dates one per line with blank lines ignored and leading trailing spaces trimmed. Each identical string increments its count in a local map. Lines appearing more than once report as date times count, such as 2026-01-01 times two. Clean lists return no duplicates plus unique count like twelve unique dates. All processing stays in your browser with no uploads, ideal for sensitive client schedules.

Why string matching matters for USA offices: January 1 2026 versus 01/01/2026 versus 2026-01-01 are different strings even when they mean the same day across Texas and New York systems. Normalize to YYYY-MM-DD first using find-replace or a date formatter before pasting. Times like 2026-01-01 10:00 versus 2026-01-01 also differ, which catches double bookings that share a day but not an hour in clinics and salons.

Common USA cleanup workflows: Export CSV from Eventbrite, Google Calendar, or Epic, copy the date column, paste here, and copy back the duplicate report into Slack. For 500-line venue calendars, duplicates surface in under a second without Excel formulas. Sort lines first if you want grouped output, though counts work unsorted. Keep original order elsewhere because this tool reports aggregates, not line numbers.

Interpreting zero versus many duplicates: Zero means each date appears once and the list is ready for import to booking software. One duplicate like July 4th times three signals triple entry from three staff members in Florida offices. Dozens of duplicates suggest a joined export with headers repeated or time zones duplicated across Eastern and Pacific feeds. Remove extras in source, re-paste, and confirm zero before publishing.

Privacy and limits: No date validation occurs beyond string equality, so February 30 counts if typed identically. For calendar validity, pair with a date validator that checks month lengths and leap years. No network means HIPAA-friendly pre-checks for appointment lists stay on device. Maximum practical size is thousands of lines limited by textarea and memory, plenty for yearly schedules.

Next steps after duplicates: Copy the duplicate block into a ticket, fix source rows, and re-run until unique. For recurring USA holidays that legitimately repeat yearly like Christmas, filter by year first or accept those as expected. Combine with remove-duplicate-lines for non-date lists and with business-hours for capacity around the remaining unique event dates.