Structured data
CSV Join and Merge
Combine two CSV exports without sending either dataset to a server.
Processed locally. Your input and output are never uploaded.
Tool overview
How CSV Join and Merge works
CSV Join and Merge matches rows from two datasets using named key columns and makes join type and duplicate behavior explicit. It keeps input and output separate, runs locally, and documents boundaries instead of making unsupported guarantees.
When two exports should meet
- matches rows from two datasets using named key columns and makes join type and duplicate behavior explicit. for a repeatable local workflow
- Review pasted or locally opened data before copying it
- Prepare output for a related PasteTidy tool
Choose keys and join behavior
- Paste the source or open a supported local file.
- Paste or open the secondary source when the comparison requires it.
- Choose the documented options and review the separate result.
- Copy or download only after checking the visible output.
Duplicate matches and output columns
- Left key columns: Comma-separated key names in the left CSV.
- Right key columns: Comma-separated key names in the right CSV.
- Join type: Rows retained when no match exists.
- Duplicate keys: How repeated right keys are handled.
- Output delimiter: Separator for the result.
Merge a lookup export
Before
Input ยท List A: id,name 1,Ana 2,Bo Input ยท List B: id,team 1,Blue 3,Red
Result
left_id,left_name,right_id,team 1,Ana,1,Blue 2,Bo,,
Keys, duplicates, and row growth
- Duplicate keys stop by default to prevent an accidental Cartesian product.
- Large input is bounded by the documented local worker limits.
- Input, options, and output are not sent to analytics or placed in URLs.
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Questions
CSV Join and Merge FAQ
Does CSV Join and Merge upload my input?
No. Processing stays in the current browser tab or its local Web Worker.
Is the result authoritative?
No. Review the output and the documented limitations before using it in a production workflow.