Clean — by Similarity API

Join two CSV filesin seconds

Match related rows across two files on a shared column — or a combination of columns. Clean reads your files, recommends the join key, and produces a merged file in seconds. No formulas, no sign-up, no install.

Drop file or browse

CSV, XLSX, or XLS · up to 10 MB

Drop file or browse

CSV, XLSX, or XLS · up to 10 MB

Join on one column — email, customer ID, order ID

How It Works

How to join two CSV files in 4 steps

Step 1

Upload

Drop your two CSV or Excel files. No signup, no install, no data stored.

Step 2

Pick a join key

Clean recommends the column — or combination of columns — that links the files. You can override it.

Step 3

Review

Preview the merged result and which rows did not match, before paying.

Step 4

Download

Get a single file with columns from both — matched rows joined, unmatched rows flagged.

Match & merge

Match related rows across two files — on one column or several.

Join two CSV files

Upload two files. Clean matches related rows on a shared column — or a combination of columns — and brings the data together. No formulas, no sign-up.

  • Match on one column (email, customer ID, order ID)
  • Match on a composite key — first name + last name + company
  • Clean recommends the join key; you can override it
  • Download a single merged file with columns from both

Why Clean

Why most online CSV merge tools cannot actually join two files

Most tools that claim to "merge" CSV files only stack them on top of each other. Joining means matching related rows across two files on a shared column — and that's where the gap shows up.

CapabilityBasic CSV mergerExcelGeneral AI assistantClean
Stack files verticallyYesYesYesNo
Match rows using one columnUsually noYesYesYes
Match rows using several columnsNoRequires setupRequires detailed instructionsYes
Recommend matching columnsNoNoSometimesYes
Compare added, removed, changed rowsNoRequires setupYesYes
Match inconsistent names or textNoLimitedYesYes
Remove duplicates within one fileSometimes exact onlyExact by defaultYesYes
No formulas requiredYesNoYesYes
No prompt requiredYesYesNoYes

For a deeper walkthrough of each approach, read our full guide on joining two CSV files by column online →

Simple Pricing

Free for small files. Pay only for large Excel & CSV jobs.

Process up to 500 rows for free. Larger files are priced per run.

$0

Up to 500 rows

  • Fuzzy deduplication
  • Multi-column matching
  • Instant download
Most Popular

Large File

$1.99+

501 – 100,000 rows

  • Up to 3,000 rows — $1.99
  • Up to 10,000 rows — $4.99
  • Up to 25,000 rows — $9.99
  • Up to 50,000 rows — $19.99
  • Up to 100,000 rows — $29.99

Monthly Unlimited

$99.99/mo

Unlimited uploads

  • Up to 10 MB per file
  • Unlimited file upload / deduplication
  • Priority customer support
  • Cancel anytime

NEED MORE?

Interested in deduping larger files?

Our API handles millions of rows with sub-second matching, bulk uploads, and programmatic access. Or reach out and we'll walk you through a custom solution — free of charge.

FAQ

Frequently asked questions

Can I combine two CSV files using a shared column?

Yes. Upload both files, pick the shared column (e.g. email, order ID, account number), and Clean joins the rows — pulling columns from File B onto matching rows in File A. If you are not sure which column connects the two files, Clean recommends one based on the actual values. See the full walkthrough in How to Join Two CSV Files by Column Online.

Can I match files using more than one column?

Yes. Clean supports composite keys — for example matching on first name + last name + company, or country + order ID. Pick multiple columns in the join step and Clean only joins rows where the full combination matches.

What if I don't know which columns connect the files?

Upload both files and Clean will read the headers and a sample of values, then recommend the most likely join key. You can override the suggestion or add additional columns before running.

What happens when a row has no match?

Unmatched rows are not silently dropped. The download includes every row from File A, with empty values where no match was found in File B, plus a flag column showing whether the row matched. You can also export only matched rows or only unmatched rows if you prefer.

Is merging CSV files the same as joining them?

Not quite. Merging usually means stacking two files vertically (appending rows). Joining means matching rows across files on a shared column and pulling fields from one file into the other — closer to a SQL JOIN or Excel's VLOOKUP / XLOOKUP. Clean does the latter.

Is my data safe to upload?

Both files are processed in memory and deleted immediately after your session. They are never written to permanent storage, never shared, and never used for any purpose other than generating your results. You can verify this in our privacy policy.

What file formats are supported?

CSV, XLSX, and XLS. Maximum 10 MB per file. If your files are larger, contact us — we can run them via the API.