JSON Key Case Converter

About this tool

JSON Key Case Converter parses your JSON, rewrites every object key into the naming convention you pick — camelCase, PascalCase, snake_case, kebab-case or SCREAMING_SNAKE_CASE — and re-serializes the document. Values are never touched: strings, numbers, booleans and null come out exactly as they went in, and keys keep their original order.

That is the everyday chore when data crosses a language boundary: a Python or Ruby service emits snake_case, a TypeScript frontend wants camelCase, a config schema wants kebab-case, and an environment map wants SCREAMING_SNAKE_CASE. Instead of writing a one-off mapper, paste the payload and switch conventions.

Renaming is recursive by default — every level of nesting, including objects inside arrays. Turn Rename keys at every nesting level off to rename only the outermost object's keys (for a root array, the keys of the objects directly inside it).

Worked example

Input:

{ "user_id": 1, "profile_data": { "first_name": "ada", "home-address": { "zip_code": "94107" } } }

With Target key case = camelCase and Indent = 2, the output is:

{
  "userId": 1,
  "profileData": {
    "firstName": "ada",
    "homeAddress": {
      "zipCode": "94107"
    }
  }
}

Switch the target to snake_case and { "lineItems": [ { "itemId": 1 } ] } becomes { "line_items": [ { "item_id": 1 } ] }. Set Indent to 0 to collapse the result onto one compact line.

How keys are split into words

Each key is split before it is rejoined in the target case:

• Any run of non-alphanumeric characters is a word boundary — first_name, home-address and first name all split the same way.
• A lowercase→uppercase hump starts a new word: firstName → first + Name.
• Acronym runs break before their last capital when a lowercase letter follows, so HTTPResponse → HTTP + Response (camelCase httpResponse, snake_case http_response) and userID → user + ID (user_id).
• Digits stay attached to the word they follow: utf8Encoding → utf8_encoding, address1 stays address1, v2Api → v2-api.

Options

• Target key case — camelCase (default), PascalCase, snake_case, kebab-case or SCREAMING_SNAKE_CASE.
• Rename keys at every nesting level — on by default; off renames only the outermost object.
• Keys to leave untouched — a comma-separated list of exact, case-sensitive key names that are copied through unchanged (Content-Type, X-Api-Key, or an object whose keys are data such as ids or dates).
• Keep leading _ $ @ sigils — on by default, so _id stays _id, __typename stays __typename and $schema_url becomes $schemaUrl. Turn it off to strip the sigil (_id → id).
• Indent spaces — 1–8 spaces per level (default 2), or 0 to minify.

Limits and edge cases

• Maximum input size 5 MB; maximum nesting depth 100 levels. Both are reported as plain errors rather than truncated output.
• Invalid JSON is rejected with the parser's exact line and column — this tool converts valid JSON, it does not repair broken JSON.
• If two different keys in the same object would become the same name (user_name and userName both → userName), the conversion fails with an error naming both keys and the JSON path instead of silently dropping one of them.
• Keys with no letters or digits at all ("___", "@") are passed through unchanged.
• Non-ASCII keys are converted with Unicode-aware casing (größe_wert → größeWert).

FAQ