What does flattening {"a":{"b":1}} actually produce?

It collapses every nesting level into one key joined by your delimiter. {"a":{"b":1}} becomes {"a.b":1} with the default dot. A deeper object like {"user":{"address":{"city":"NYC"}}} flattens to {"user.address.city":"NYC"}. The value 1 stays the number 1, not the string "1" — only the keys are rewritten, the leaf values are copied through untouched.

Should arrays use a.0 or a[0]?

Both are supported, pick per your downstream tool. With numeric-key style, {"tags":["x","y"]} flattens to {"tags.0":"x","tags.1":"y"}. With bracket style it becomes {"tags[0]":"x","tags[1]":"y"}. Bracket style is unambiguous when object keys might themselves be numbers; numeric-dot style is more common in .env and config tooling. Use the same setting when you unflatten or the array rebuilds as an object.

How do I get the nested object back?

Switch the direction to Unflatten and paste the flat object. Keys are split on your delimiter and rebuilt level by level: {"user.address.city":"NYC"} becomes {"user":{"address":{"city":"NYC"}}}. If a segment is a number (or a bracket index under bracket style) it rebuilds as an array element, so {"tags.0":"x","tags.1":"y"} returns {"tags":["x","y"]}. Flatten then unflatten with matching options is a clean round-trip.

Can I use a custom delimiter instead of a dot?

Yes. The dot is the default, underscore is one click away, and you can type any custom separator — handy when your keys already contain dots. For example flattening {"file.name":{"ext":"json"}} with a dot is ambiguous, but with "/" you get {"file.name/ext":"json"} where the literal dot is clearly part of the key, not a level boundary. Use the same delimiter to unflatten.

Where is flattening actually useful?

Three common places: feeding nested config into a flat key-value store (Consul, etcd, .env, AWS Parameter Store), mapping i18n translation trees to flat message keys for translators, and turning a nested record into spreadsheet columns where each leaf is one column header. Diffing two configs is a fourth — a change three levels deep shows up as one flat key instead of hiding inside nested braces.

Are my numbers and booleans preserved, and is the JSON uploaded?

Types are preserved: 5432 stays a number, true stays a boolean, null stays null — flatten and unflatten only rewrite keys, never coerce leaf values to strings. And nothing uploads: parsing and the recursive walk run entirely in your browser tab with no network request, so it is safe to paste internal config. The shareable URL does encode your input, so use copy-paste for anything secret.

Load nested config into a flat .env or key-value store

Your app config lives as nested JSON, but the deploy target wants flat keys: Consul, etcd, a .env file, or AWS Parameter Store. Paste {"db":{"host":"localhost","port":5432}}, flatten it, and you get db.host and db.port as top-level keys you can write straight to the store. Pick the underscore delimiter and DB_HOST / DB_PORT drops into an env file without another rename pass.

Diff two configs that differ three levels down

Two service configs look identical at a glance but one request fails in staging. Flatten both, paste the flat versions into a diff tool, and the one line that changed shows up as a single key like features.checkout.retryLimit instead of being buried inside three nested braces you have to expand by eye.

Map an i18n translation tree to flat message keys

Translation files are nested by namespace: {"home":{"title":"Hi"}}. Most translation platforms and gettext-style catalogs want flat keys like home.title. Flatten the tree, hand the flat list to translators, and unflatten their returned file back into the nested shape your i18n library loads. Round-trips cleanly with no manual key rebuilding.

Turn a JSON object into spreadsheet-friendly columns

You want one nested record as a single spreadsheet row. Flatten it so every leaf becomes one column header (address.city, address.zip, tags.0, tags.1), paste into your sheet, and the structure that JSON encoded as nesting becomes plain columns. Switch array style to a[0] if your import expects bracket indices instead of numeric dot keys.

JSON Flatten / Unflatten — Nested JSON to Dot Notation

Flatten nested JSON to dot-notation keys and unflatten it back — choose the delimiter and array style, types preserved, browser-only.

Runs locally
Category Developer & DevOps
Best for Formatting, validating, shrinking, or inspecting code-adjacent text.

Flatten nested JSON to dot-notation keys, or unflatten flat keys back to a nested object. {"a":{"b":1}} ⇄ {"a.b":1}. Pick the delimiter and the array style (a.0 or a[0]); leaf types — numbers, booleans, null — are preserved.

Direction

Delimiter

Array style

Input JSON

✓ Valid JSON in

Output JSON

{
  "a.b": 1,
  "tags.0": "x",
  "tags.1": "y",
  "ok": true
}

What this tool does

Flatten nested JSON into single-level dot-notation keys, and unflatten flat keys back into the original nested object. Paste any JSON: a nested object like {"a":{"b":1}} becomes {"a.b":1}, and the reverse rebuilds the tree exactly. Pick how arrays are written — numeric keys (a.0) or bracket indices (a[0]) — and choose the delimiter (dot, underscore, or a custom separator) so a literal dot in your keys never collides with a level boundary. Every leaf keeps its JSON type: numbers stay numbers, booleans stay booleans, null stays null. Invalid JSON gets a friendly error with the line and column. One-click copy, indented output, and a shareable URL that reproduces your exact input and options. 100% client-side, nothing uploaded.

Tool details

Input: Text + Numbers + Structured content; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 9 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Developer & DevOps · Developer; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How JSON Flatten / Unflatten fits into your work

Use it in the small gaps between coding, reviewing, debugging, and shipping.

Developer jobs

Formatting, validating, shrinking, or inspecting code-adjacent text.
Preparing snippets for documentation, tickets, commits, or handoff.
Checking a small payload quickly without switching tools.

Developer checks

Run irreversible transforms like minify or obfuscate on a copy.
Keep secrets out of pasted snippets unless the tool explicitly stays local.
Use your normal tests or linter before shipping transformed code.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Load nested config into a flat .env or key-value store
Your app config lives as nested JSON, but the deploy target wants flat keys: Consul, etcd, a .env file, or AWS Parameter Store. Paste {"db":{"host":"localhost","port":5432}}, flatten it, and you get db.host and db.port as top-level keys you can write straight to the store. Pick the underscore delimiter and DB_HOST / DB_PORT drops into an env file without another rename pass.
Diff two configs that differ three levels down
Two service configs look identical at a glance but one request fails in staging. Flatten both, paste the flat versions into a diff tool, and the one line that changed shows up as a single key like features.checkout.retryLimit instead of being buried inside three nested braces you have to expand by eye.
Map an i18n translation tree to flat message keys
Translation files are nested by namespace: {"home":{"title":"Hi"}}. Most translation platforms and gettext-style catalogs want flat keys like home.title. Flatten the tree, hand the flat list to translators, and unflatten their returned file back into the nested shape your i18n library loads. Round-trips cleanly with no manual key rebuilding.
Turn a JSON object into spreadsheet-friendly columns
You want one nested record as a single spreadsheet row. Flatten it so every leaf becomes one column header (address.city, address.zip, tags.0, tags.1), paste into your sheet, and the structure that JSON encoded as nesting becomes plain columns. Switch array style to a[0] if your import expects bracket indices instead of numeric dot keys.

Common pitfalls

Picking a delimiter that already appears in your keys. If a key is "user.name" and you flatten with ".", unflatten can no longer tell the literal dot from a level boundary. When keys contain dots, switch to "_" or a custom delimiter that never shows up in your data.
Expecting unflatten to keep your custom array style automatically. Flatten with a[0] but unflatten with the a.0 setting and the numeric segments rebuild as object keys, not an array. Use the same delimiter and array-bracket option on both directions, or the round-trip silently changes shape.
Assuming numbers and booleans become strings. They do not — flatten preserves the JSON type of every leaf, so 5432 stays a number and true stays a boolean. If you need everything stringified for a key-value store that only accepts strings, do that conversion after flattening, not before.

Privacy

Flatten, unflatten and JSON parsing all run as plain JavaScript inside your browser tab — JSON.parse plus a small recursive walk over the object. No JSON ever uploads, nothing is logged, and there is no network request carrying your data. The one thing that leaves the page: the shareable URL encodes your input and options in the query string, so a link pasted into chat records that payload in the recipient server's access log. For confidential config or secrets, use the copy button and paste the text instead of sharing the URL.

FAQ

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JSON Flatten / Unflatten — Nested JSON to Dot Notation

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How JSON Flatten / Unflatten fits into your work

Developer jobs

Developer checks

Good next steps

Real-world use cases

Load nested config into a flat .env or key-value store

Diff two configs that differ three levels down

Map an i18n translation tree to flat message keys

Turn a JSON object into spreadsheet-friendly columns

Common pitfalls

Privacy

FAQ

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