Group Concatenate JSON Files Online
Concatenate text values within each group in JSON files directly in your browser. Group rows by a column and join the values of another column into a single delimited string — no upload required.
Drop your .json file here
or click to browse — max 50 MB
About this tool
Collapse rows in a JSON file by grouping them on a column and joining the values of another column into a single delimited string per group — equivalent to SQL's string_agg (or GROUP_CONCAT in MySQL). For example, group by customer and concatenate all their order IDs into one cell. You can set a custom separator, control the order of values within each group, and rename the output column. The result is a summarised file with one row per group, ready to download. All processing runs locally in your browser.
Frequently Asked Questions
What does group concatenate do to a JSON file?
It collapses multiple rows that share the same group-by column value into a single row. The values from the chosen column are joined into one delimited string — for example, all product names for each customer in a single cell.
Can I control the order of values inside each group when concatenating a JSON file?
Yes. Set the Order By column and choose ascending or descending. Without an order, values within each group appear in their physical storage order, which may not be deterministic.
What separator should I use when concatenating values in a JSON file?
Common choices are comma-space (", "), pipe (" | "), semicolon ("; "), or a newline ("\n"). Avoid using a separator that also appears inside the values — or use the SQL Query tool to wrap values in quotes before concatenating.
Is my data private?
Yes — completely. Your file is never uploaded to any server. Everything runs locally in your browser using WebAssembly — processing happens entirely inside your tab. Once you close the tab, nothing is retained.
What is the maximum file size?
The free limit is 50 MB. For larger files, performance depends on your device's available memory — most modern machines handle 500 MB to 1 GB comfortably.
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