How do I merge multiple CSV files into one?

Choose all the files above, leave the header option ticked if they have column names, and press Merge files. Columns with the same or equivalent names are lined up, extra columns are kept, and you download one CSV. Nothing is uploaded; the files are read by your browser.

How do I combine multiple CSV files into one Excel spreadsheet?

Merge them here into one CSV, then open that CSV in Excel and save it as .xlsx. That gives you one sheet with every row, rather than Excel's Power Query route, which needs the files in one folder and the same columns in each.

How do I merge CSV files in CMD?

On Windows, copy *.csv merged.csv in the folder joins the files byte for byte. It repeats every file's header row inside the data and can't line up columns that are in a different order, which is why a header-aware merge is safer for contact lists.

Can I merge two CSV files with different columns?

Yes. Columns are matched by name rather than position, with common synonyms such as Email and E-mail Address treated as one. A column that only one file has is added to the merged file and left blank for rows from the other.

Is it safe to merge CSV files online?

With this tool, yes: the files are read and merged in your browser and never uploaded. Up to 20 files of 25 MB each, and 50,000 rows merge in about a second.

Merge CSV files and email lists into one

Choose two or more CSV files and this tool stacks them into one, matching columns by header name, so Email in one export and email_address in another end up in the same column. Columns that only one file has are kept, and duplicate email addresses are removed, keeping the first row. Everything runs in your browser.

CSV files to merge

Choose CSV files (select several at once)Runs in your browser. Nothing is uploaded.

Each file starts with a header rowColumns are matched by name, so Email, E-mail and email_address land in one column. Untick to join files by column position instead.Remove duplicate emails after mergingCase-insensitive. The first row for each address is kept, so put your most complete file first.Add a source_file columnRecords which file each row came from, so you can trace it later.

SimpleAPI

Sample result

2 files merged into 3 rows, with 1 duplicate email removed.

Rows out: 3
Files: 2
Rows in: 4

What this means for you

One clean file instead of several, so no one gets the same email twice.

Next step:Verify the cleaned list

Matches columns by header name and synonyms
Email and E-mail Address land in one column
Optional dedupe on the email column
Optional source_file column per row

Merge
CSV
Dedupe

By SimpleVerifier Team · Last updated October 17, 2026 · Runs in your browser; nothing you paste is sent to us

How do I merge CSV files into one?

Choose your CSV files. You can select several at once and add more afterwards. Put the file with the most complete rows first, because its rows win when an email appears twice. Up to 20 files at a time, each up to 25 MB.
Leave "header row" ticked if each file starts with column names. Untick it for headerless files, which are then joined by column position.
Press Merge files. The summary lists each file's rows and any columns it added that earlier files didn't have.
Check the preview, then download the merged CSV.

Example

You enter: Two files, crm.csv and webinar.csv, with 4 rows between them and Email and E-mail Address as the email headers.
You get: One merged.csv with 3 rows under a single Email column, 1 duplicate email removed, and a source_file column naming where each row came from.
Limits: Up to 20 files at a time, each up to 25 MB, merged in your browser.

How do I merge CSV files with different columns?

Match them by header name, not by position, which is what this merger does. Every tool exports the same fields under different names. HubSpot writes Email, Mailchimp Email Address, a form tool email_address and a spreadsheet someone typed E-mail. Joining those files by position puts phone numbers under the email heading, which is the usual way merged lists get broken.

This merger compares headers after lower-casing them and dropping spaces, dashes and underscores, then folds common synonyms together: email, e-mail and email address; first name, fname and given name; last name and surname; company, organisation and account name. Anything it doesn't recognise is matched by exact name, and a column that only one file has is added to the end, blank for rows from the other files.

If two columns in the same file share a name, both are kept as separate columns rather than one overwriting the other.

Can I combine multiple CSV files into one without duplicates?

Yes. With deduplication on, the first row for each email address is kept and the repeats are dropped. With deduplication on, addresses are compared in lower case with surrounding spaces removed, so Jane.Doe@ and jane.doe@ count as one. The first row seen is kept, reading the files in the order listed. Rows with an empty email cell are always kept.

This is a simple first-row-wins rule, not a field-by-field merge. If you need the phone number from one file and the job title from another on the same row, merge here first and then use compare email lists to see which addresses appear in which file. For Gmail dot and +tag variants, run the result through remove duplicate emails with the Gmail option on.

Should I verify a merged email list before sending?

Yes, because a merged list carries the dead addresses of every file that went into it. A merged list is usually older on average than any one export, and lists lose valid addresses over time as people change jobs and mailboxes close. One merged file also mixes sources you trust with ones you don't, such as a trade-show scan beside your CRM.

Before a send, remove what can't be delivered. Bulk syntax checking catches malformed addresses for free; whether a mailbox still exists needs a check against the receiving server, which is what a hard bounce would otherwise tell you the expensive way.

Is this better than merging CSV files in Excel or CMD?

	This tool	Excel Power Query	copy *.csv in CMD
Different column orders	Matched by name	Matched by name	Joined by position
Header rows	Kept once	Kept once	Repeated inside the data
Email vs E-mail Address	Treated as one column	Two columns	Not handled
Duplicate emails	Removed (optional)	Separate step	Not handled
Setup	Choose files, press Merge	Folder query and transforms	One command

Who uses this tool, and for what?

Cold emailers: Combine lead exports from Apollo, a scraper and a purchased list into one sending file, with one column per field and no address twice.
Event marketers: Join registration, attendance and badge-scan exports from each event into one follow-up list, with a source_file column so you know where each lead came from.
Agencies: Clients send lists from different tools with different headers. Merge them into one consistent file before you verify or import it.
Ops and RevOps: Consolidate monthly CRM exports or regional sheets before a migration, then check what overlaps with compare email lists.

What can’t this tool tell you?

Duplicate rows are resolved first-row-wins; fields from the dropped row are not merged into the kept one.
Only exact header names and a short synonym list are matched. A column called Contact won't be paired with Email automatically.
Gmail dot and +tag variants count as different addresses here; use remove duplicate emails with the Gmail option for those.
Merging doesn't check whether any address still works.

Common questions

How do I merge multiple CSV files into one?: Choose all the files above, leave the header option ticked if they have column names, and press Merge files. Columns with the same or equivalent names are lined up, extra columns are kept, and you download one CSV. Nothing is uploaded; the files are read by your browser.
How do I combine multiple CSV files into one Excel spreadsheet?: Merge them here into one CSV, then open that CSV in Excel and save it as .xlsx. That gives you one sheet with every row, rather than Excel's Power Query route, which needs the files in one folder and the same columns in each.
How do I merge CSV files in CMD?: On Windows, copy *.csv merged.csv in the folder joins the files byte for byte. It repeats every file's header row inside the data and can't line up columns that are in a different order, which is why a header-aware merge is safer for contact lists.
Can I merge two CSV files with different columns?: Yes. Columns are matched by name rather than position, with common synonyms such as Email and E-mail Address treated as one. A column that only one file has is added to the merged file and left blank for rows from the other.
Is it safe to merge CSV files online?: With this tool, yes: the files are read and merged in your browser and never uploaded. Up to 20 files of 25 MB each, and 50,000 rows merge in about a second.

Sources

A tidy list can still be full of dead addresses.

Extracting, deduplicating and syntax checks all work on the text of an address. None of them can tell whether the mailbox exists. Only the server that hosts it can answer that, through an SMTP check, and that is what the paid product does.

Upload the cleaned file as it is: CSVs up to 100,000 rows
A real SMTP mailbox check on every row, with catch-all detection
Small list? $9 one-time covers 2,500 emails, no subscription

Get started — $29.99/mo See the published limits first

One plan, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.