Merge JSON Files Online

    Combine API responses, config files and exported records into one JSON document. Arrays are concatenated and objects merged key by key, all locally in your browser with nothing sent to a server.

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    Merging JSON Is Not Like Merging Rows

    Arrays Concatenate, Objects Merge

    The right merge depends on what your files hold at the top level. Files containing arrays of records are concatenated end to end, which is what you want when combining paginated API responses into one dataset. Files containing a single object are merged key by key instead. Mixing the two shapes in one operation is ambiguous, so FileMerger asks you to choose rather than guessing and silently producing something wrong.

    When Two Files Define the Same Key

    Merging objects raises the question of what happens when both files contain the same key. FileMerger applies a last-file-wins rule at each level, so the file loaded later overrides earlier values for keys they share. Nested objects are merged recursively rather than replaced wholesale, meaning a nested block present in both files keeps the union of its keys instead of losing the earlier file’s entries. Load your files in deliberate order when overriding matters, such as merging a defaults file with an environment-specific one.

    Validation Before Anything Else

    A merge is only as good as its inputs, so every file is parsed and validated before the operation starts. If a file contains a trailing comma, an unquoted key or a stray control character, the merge stops and reports which file and which position is at fault rather than producing a half-valid result. Files exported from logging systems sometimes contain newline-delimited JSON, where each line is a separate document rather than the file being one array; that format needs converting to a proper array first, and the validator will tell you when it detects it.