JSON Error Locator

Find where your JSON breaks, not just that it broke

Parsers tell you something is wrong and stop at the first mistake. Paste the document above and this tool tells you where — a 1-based line, a character-counted column, and a 0-based offset for every syntax problem it finds — plus a plain-English cause, a concrete fix, and a caret pointing at the exact character. Everything runs in your browser; the text is never uploaded.

What it names

• Trailing commas — [1, 2, ], {"a": 1,}
• Single-quoted strings and keys — {'a': 'b'}
• Unquoted keys — {name: "Ada"} — and unquoted bare-word values
• Missing commas between members/elements, and a missing (or = instead of :) colon
• Mismatched or unclosed brackets — {"a": 1], {"a": {"b": 1}
• Unterminated strings, pointing back at the opening quote that started them
• Invalid escapes — "C:\Users", and \u escapes with fewer than four hex digits
• Unescaped control characters — a raw line break or tab inside a string
• Invalid numbers — .5, 1., +1, 007, 0x1F
• JavaScript/Python literals — undefined, NaN, Infinity, True, None
• Comments — // line and /* block */
• Extra content after the document's single top-level value

Worked example

Input:

{
  "name": "Ada",
  "tags": [1, 2,]
}

Diagnosis (default settings):

Invalid JSON — 1 issue found.
A parser stops at line 3, column 17.

1. Line 3, column 16 (offset 34) — trailing comma
   Cause: this comma is the last thing in the array; JSON does not allow a comma before ].
   Fix:   delete this comma (or add another value after it before the ]).

   1 | {
   2 |   "name": "Ada",
   3 |   "tags": [1, 2,]
     |                ^
   4 | }

Switch Result format to machine-readable JSON and the same run returns {valid, issue_count, issues[], parser_stop, summary} — one object per issue with kind, label, line, column, offset, explain, fix and the snippet — ready to pipe into a script or a CI check.

Valid input still tells you something

A document that parses returns a summary instead of an error: the top-level value's type, how many members or elements it holds, the nesting depth, and the line/byte count.

Limits and edge cases

• Input is capped at 1 MiB and nesting at 200 levels; deeper input reports nesting too deep, which in practice almost always means an unclosed bracket further up.
• A position is where the problem was detected, which can be just after the real mistake. For a missing comma or bracket, check the end of the previous line — the report repeats this note for exactly that reason.
• Columns count characters, not bytes, matching what your editor's cursor shows. "héllo" is 6 bytes but 5 characters wide.
• An unterminated string ends the scan. Everything after it was swallowed by the open quote, so any further finding would be an artefact rather than a real error.
• Syntax only. This tool diagnoses; it does not rewrite your JSON and does not check it against a JSON Schema.
• At most 50 issues are listed — a badly mangled file cascades, and the first few are the ones worth fixing.

FAQ