Trim the whitespace from every string in a JSON document

About this tool

json-trim-strings walks a valid JSON document and rewrites the whitespace of every string value, at any depth, inside objects and arrays. Structure is never touched: numbers, booleans and nulls are copied through unchanged, key order is preserved, and arrays keep their length and their positions.

That makes it the opposite of a minifier. A minifier removes the whitespace between tokens and deliberately protects the inside of every quoted string. Here the structure is fine and the payload is dirty — " Berlin" and "Berlin" are different join keys, a padded " 42 " breaks a downstream cast, and a duplicate check quietly reports two customers where there is one.

The defaults are the safe ones: trim both ends, leave the inside of the string exactly as it was, treat the full Unicode whitespace set as blank, and copy object keys verbatim. Everything past that is opt-in.

Worked example

Input, with the defaults (trim both ends, keep the interior, indent 2):

{"name": "  Ada  ", "city": " Berlin ", "tags": [" x ", "y  "], "visits": 7}

Output:

{
  "name": "Ada",
  "city": "Berlin",
  "tags": [
    "x",
    "y"
  ],
  "visits": 7
}

visits stayed the number 7 — a trimmed string is still a string here, and nothing is retyped.

Choosing the options

• Trim which end — both (default), leading, trailing, or none to leave the edges alone and rewrite only the interior.
• Whitespace inside the string — keep (default) makes this a pure trim; collapse turns every inner run into a single space, so " Ada Lovelace " becomes "Ada Lovelace"; remove deletes it, so " AB 12 CD " becomes "AB12CD" — useful for SKUs, IBANs and part numbers.
• What counts as whitespace — unicode (default) also catches the invisible characters that survive a spreadsheet or web copy-paste: non-breaking space U+00A0, narrow no-break space U+202F, ideographic space U+3000. ascii limits it to space, tab, newline, carriage return and form feed, so an NBSP stays part of the content.
• Also trim object keys — off by default. When on, a key literally named " first name " becomes "first name".
• Values left empty by the trim — a value that was nothing but whitespace becomes "" (default), null, or is dropped from its object.
• Only these keys / Keys to never touch — limit the pass to named fields, or protect fields whose padding is meaningful. Both match key names at any depth, and a key in both lists is skipped.
• Indent — 0 minifies onto one line, 2 (default) through 8 pretty-print.

Everything runs locally in WebAssembly in your browser. Nothing is uploaded, there is no account, and there is no daily quota.

Limits and edge cases

• The input must already be valid JSON. Comments, trailing commas and unquoted keys are rejected with the line and column of the problem — repair the document first.
• The input cap is 5 MB (5,000,000 bytes); the whole document is parsed into memory.
• Values are never retyped. A trimmed " 42 " becomes the string "42", not the number 42 — use json-coerce-types for that.
• Zero-width characters (U+200B zero-width space, U+FEFF byte-order mark) are content, not whitespace, under both whitespace settings — zero-width-cleaner removes those.
• With key trimming on, two keys in the same object that trim to the same name are an error, not a silent overwrite.
• Only these keys matches key names, so a bare top-level string document has no key and is left alone when the list is non-empty.
• Inside an array, a value emptied by the trim becomes null rather than disappearing, so indexes and array length never shift.
• Indent values outside 0–8 are clamped rather than rejected.

FAQ