35 / Data
Merge CSV Files — Stack Rows or Join by Key
Combine CSV or TSV files by stacking aligned rows or joining records on a shared ID, email, SKU, or other key.
Private data assembly
Stack rows or join records by a shared key.
Choose two or more CSV or TSV files. Siftlet aligns columns by header, shows the exact output shape, and exports one portable CSV without sending a row away.
- Union or shared-column row stacking
- Full, left, or inner joins by ID, email, SKU, or another key
- Quoted commas, tabs, semicolons, and multiline cells
Waiting for local delimited files.
Local merge set
2 filesInputs
Files and detected shapes
Output preview
Stacked rows
Choose at least two readable files.
Field note
How to merge CSV files without breaking the columns
Use Stack rows when files contain the same kind of record, such as monthly exports. Union keeps every header and leaves missing cells blank. Intersection keeps only headers found in every file. The optional source column makes each row traceable.
Use Join by key when files describe different facts about the same record. Pick a shared ID, email, SKU, or other key. A full outer join keeps every key, a left join keeps keys from the first file, and an inner join keeps only keys found in every file. Repeated keys create multiple output combinations rather than silently dropping data.
The preview and report expose row counts, duplicate-key groups, delimiters, and output columns before download. For a single dirty file, use the related Large CSV Viewer & Cleaner instead.