Match two tables by a shared identifier and append lookup fields, such as prices or inventory, to a base product CSV.
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CSV input settingsChoose the corresponding file again after changing a setting.
Choose a CSV file or try the sample.
What this tool does
Join CSV Files by Key
Load a base CSV and a lookup CSV, then select one key column from each. A left join keeps every base row; an inner join keeps only matched rows. The result reports matched, base-only and lookup-only key counts.
How to use it
Choose the base and lookup CSV files and confirm their encoding, delimiter and headers.
Select the corresponding key column on each side and choose a left or inner join.
Review the joined rows, renamed collisions and match counts, then download CSV.
Common tasks
Append price and inventory columns to a product export by product ID.
Match customer and order extracts by an exact customer identifier.
Inspect duplicate, empty and unmatched keys before using the joined CSV.
Privacy and local processing
Local files are read by a dedicated browser worker and are not uploaded to an application server. File contents and filenames are not included in analytics events. Loading a public URL is an explicit direct request from your browser and may fail when the remote server blocks CORS.
Supported edge cases
Keys use exact string matching. 00123 and 123, ABC and abc, and values with surrounding spaces are different keys.
Base keys may repeat. A duplicate lookup key blocks the join because there is no single row to append. Empty keys are rejected on both sides.
When a lookup header collides with a base header, the lookup name receives _right and a numeric suffix if needed.
Frequently asked questions
How is this different from merging CSV files?
A file merger stacks rows vertically. This join matches identifiers and appends columns horizontally.
What happens when a key appears more than once?
Repeated base keys are joined normally. Duplicate lookup keys stop the join because the tool cannot choose a single row to append.