Remove duplicate rows from CSV
Exact duplicates, near-duplicates (typos, name variations), or duplicates by a key column like email — upload your CSV and CSViser removes them all, with a preview before you apply.
Upload your CSV to deduplicate
CSV, XLSX, or JSON — any size
Free account — takes 10 seconds to sign up
After upload: go to the Deduplicate tab → choose All columns or a key column → Preview → Apply.
Where do duplicate rows come from?
Duplicate rows accumulate in three common ways. The first is repeated exports: you export your CRM contacts on Monday, add more on Thursday, export again, then concatenate the files — every contact from the first export appears twice. The second is scraper output: web scrapers often revisit the same pages during pagination or retry logic, producing multiple copies of the same record. The third is form submissions: users submit the same lead form more than once, or a webhook fires twice due to a network retry.
Near-duplicates are harder to spot: the same person with a typo in their last name (Johnson vs Johnsen), the same company listed twice with slightly different formatting (Acme Corp vs ACME Corporation), or the same email address with different capitalisation ([email protected] vs [email protected]).
Two deduplication modes
Exact deduplication compares every column of every row and removes rows that are byte-for-byte identical to an earlier row. This is fast and safe — if two rows differ by even a single character, neither is removed.
Fuzzy deduplication uses normalised Levenshtein distance to find near-matches within a single key column (e.g. email or company name). You set a similarity threshold (default 85%) — rows whose key values are at least that similar are grouped, and all but the first are removed. The preview shows exactly which rows will be deleted and at what similarity score, so there are no surprises.
Deduplication by key column
When you only care about one column — for example, ensuring each email address appears exactly once — select that column from the "Compare by" dropdown. CSViser keeps the first occurrence and removes all later rows with the same value in that column, regardless of what the other columns contain.
Frequently asked questions
Which duplicate is kept — the first or the last?
The first occurrence is always kept. If you want to keep the most recent version of a record, sort the file by a date column (newest first) before deduplicating — the Sort tab handles that in the same session.
Can I preview what will be deleted before applying?
Yes. For all-columns deduplication, a preview table showing up to 20 duplicate rows appears automatically. For single-column and fuzzy deduplication, click Preview first — you'll see every affected row with similarity percentages before anything is changed.
How large a file can I deduplicate?
The free plan processes files up to 500 rows. Pro handles files of any size. Fuzzy deduplication is capped at 50,000 rows to keep response times reasonable.