01
Check the replacement preview
Importing a file, loading an example or clearing the input proposes a replacement first. Apply it after checking the preview; Undo restores the previous input, result and settings.
JSON tools
JSON flattenkeep paths and types together
Choose flatten or restore, then run the conversion. Changing the input or options requires another run.
JSON flatten
JSON input
Result
Copy and download include the full result, beyond the visible preview.
JSON stays in browser memory and is not uploaded or saved.
Versioned format: k: marks object keys, i: marks array indexes; backslash escapes the separator and backslash. An empty path is the root.
Result is out of date; copy and download are disabled.
Use JSON flatten when nested configuration or an API response makes it difficult to compare individual fields. Each terminal value receives a path, so a deeply buried setting can be inspected without following the whole object tree.
The output is a versioned JSON envelope, with settings and typed paths alongside the values. JSON unflatten reads that envelope; it does not guess whether an arbitrary dotted key represents an object property or an array index.
Why use JSON flatten?
Tell numeric keys apart from indices
JSON flatten marks object keys with k: and array indices with i:. An object property named "0" therefore remains different from the first array element. Escaped separators also distinguish a literal dotted key from a nested path.
Choose how much of an array to expose
Use JSON flatten with indices to see each nested array value, or keep arrays as complete values when their contents should travel together. Empty objects and arrays remain present, so restoration does not lose an empty configuration section.
Prepare a round trip
02
Pick the array strategy before running
Indices expands arrays; Keep retains each complete array. The separator is one ASCII punctuation character except a colon or backslash. Conversion runs manually, and edited settings make the previous result stale.
03
Restore from the complete envelope
Use result previews a replacement and switches direction when applied. Keep the envelope metadata and all entries for restoration. The visible preview grows by 5,000 characters; copy and download include the entire accepted result.
Paths that carry their meaning
Explicit key and index types
Object segments begin with k: and array segments with i:. The empty path represents the root, including a scalar, null or an empty container.
Reversible separator escaping
A separator inside an object key and a literal backslash are escaped with a backslash. Paths must use the canonical spelling expected by this format.
Number spelling retained
Large integers, -0, decimals and exponent tokens such as 1e999 are preserved as JSON number text. This conversion does no arithmetic and does not round them through JavaScript numbers.
Whole-document validation
Duplicate keys, conflicting paths, sparse arrays and mixed container types are rejected. A failed conversion never offers a partial result as a successful export.
Format and processing limits
- Restore this format only
- Restoration accepts the heyutils-json-flat-v1 envelope produced here, with separator, arrays and entries. Generic dot-path maps, JSONPath expressions and other flatten formats are not interchangeable.
- Strict JSON input
- Comments, trailing commas and duplicate object keys are rejected. Valid number tokens are preserved, including values beyond ordinary floating-point range; each number token is limited to 1,000 characters.
- Bounded documents
- Input and output are each limited to 500,000 characters; imported files to 500,000 bytes. Maximum depth is 100 and the node budget is 50,000. Exceeding a limit causes an error instead of truncated output.
- Canonical array paths
- Expanded array indices must be below 10,000 and form a dense array. Keep may retain longer arrays within the node budget, but its restoration rejects i: paths. Prefix conflicts, mixed container types and noncanonical paths are rejected.
- Local conversion
- Data is processed in browser memory. The tool does not fetch source URLs, save conversion history or export CSV. Reloading discards the current work.
JSON flatten questions
How can I restore JSON containing arrays?
Keep the complete envelope and choose restore, or apply Use result to switch direction. JSON flatten records whether arrays were expanded or retained and uses typed indices instead of inferring arrays from numeric property names.
How do I flatten a nested JSON array?
Choose the indices strategy. Each array element receives an i: segment, including arrays inside objects or other arrays. Keep leaves the complete array at its current path when individual elements do not need separate entries.
How do I reverse the flattening of nested arrays?
Run restore on the envelope from this tool. Arbitrary jq output or another dotted-key map needs conversion to this format first; changing only the mode does not translate a foreign path syntax.
What is a practical way to flatten and unflatten nested objects?
For a one-off inspection, run the browser conversion and check a round trip before copying the result. This page makes no fastest-runtime claim; for automated pipelines, use a library whose path format matches the system receiving your data.
Can I flatten JSON nested across several levels?
Yes. Nested objects and indexed arrays are traversed up to the depth and node limits. Keys include each typed segment, so a deeper value remains associated with its source location.
Found a path that does not round-trip?
Check one round trip
Try JSON flatten on an example, inspect the typed paths, then use the result to restore the original structure before working with a larger document.