CSV & JSON Data Merger

It combines multiple CSV and/or JSON files — with the same or similar structure — into one unified dataset, previewed as a table and downloadable as CSV or JSON. Mixed file types are fine in the same merge: each file is parsed according to its own format, then everything is worked with as the same row/column shape from that point on.

These are two different, genuinely common ways to combine data. "Stack rows" appends every file's rows into one longer list — use it when your files are separate batches of the same kind of record (e.g. exports from different months). "Join on key" is a relational join: it lines up rows ACROSS files that share the same value in a column you pick (like "id" or "email") — use it when your files describe the same set of things but each contributes different columns (e.g. one file has contact info, another has order history, joined on a shared customer ID). Stacking multiplies rows; joining multiplies columns.

For "Stack rows": columns that only appear in some files are still included — the union of every column across all files — and rows from a file that lacked a given column simply get an empty cell for it, rather than the tool dropping the column or misaligning data. For "Join on key": the join column has to be common to every file (rename columns first if they're named differently, like "email" vs. "Email Address" — this tool includes a simple per-file rename step for exactly that). A left join keeps every row from the first file even when a match isn't found elsewhere; an inner join keeps only rows that matched everywhere.

No — every file is parsed, merged, and previewed entirely in your browser. Nothing is uploaded to a server.