Fill Empty Values in JSON Files Online

What counts as a null or empty value in a JSON file?

SQL NULL values and empty strings are both treated as missing and will be filled. Values that are whitespace only are not automatically treated as null — use the Trim tool first if needed.

Can I fill numeric and text columns with different values in a JSON file?

Yes. Set a text fill value for string columns and optionally a separate numeric fill value for number columns. Enable the "Also fill numeric nulls" option to apply both.

What if I only want to fill nulls in specific columns of a JSON file?

This tool fills all eligible columns. For column-level control, use the SQL Query tool and write SELECT COALESCE("col", 'replacement') AS "col" for each column you want to fill.

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.