TidyCSV

Deduplicate an Email List (CSV)

Remove duplicate contacts from an email list by deduping on the email column — locally, so subscriber data never leaves your browser.

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Why this matters

Email lists accumulate duplicates fast: the same person signs up twice, you merge a webinar list into your master list, or an export overlaps a previous one. Send to that list and you pay to deliver twice, annoy subscribers, and skew your open-rate maths.

Most ESPs charge by contact or by send, so duplicate addresses cost real money — and a hard-bounce on a duplicated bad address counts against your sender reputation twice.

TidyCSV dedupes on the email column specifically, so two rows with the same address collapse to one even if the name or signup-date columns differ. Because it all runs in your browser, a list full of personal email addresses is never uploaded to a third-party cleaner.

How to do it with TidyCSV

  1. Drop your contact CSV into TidyCSV.
  2. Enable "Remove duplicate rows" and choose your Email column as the dedupe key.
  3. Optionally turn on "Trim whitespace" so " ada@example.com " and "ada@example.com" are treated as the same address.
  4. Check the removed-rows sample, then export your clean list ready to import into your ESP.

Before & after

Messy input (highlighted rows get removed)
EmailFirst NameSigned Up
ada@example.comAda2026-01-04
grace@example.comGrace2026-02-11
ada@example.comAda L.2026-03-02
alan@example.comAlan2026-03-08
Clean output
EmailFirst NameSigned Up
ada@example.comAda2026-01-04
grace@example.comGrace2026-02-11
alan@example.comAlan2026-03-08

FAQ

Yes. When you pick the Email column as the key, rows are matched on the address alone, so "Ada" and "Ada L." with the same email collapse to a single row — the first one kept.

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Related

Remove duplicate rowsClean before CRM importTrim whitespace