Common JSON parse errors (and how to fix them)

JSON is strict. Many “JSON parse errors” happen because the input is actually JavaScript object literal syntax (or a config format) rather than valid JSON.

1) Trailing commas

JSON does not allow a comma after the last item in an object/array. 

// ❌ invalid JSON
{
    "a": 1,
}

// ✅ valid JSON
{
    "a": 1
}

2) Single quotes

JSON strings and object keys must use double quotes.

// ❌ invalid JSON
    { 'a': 'b' }

    // ✅ valid JSON
    { "a": "b" }

3) Comments

JSON doesn’t support // or /* */ comments. 

// ❌ invalid JSON
{
    "a": 1 // comment
}

4) Unquoted keys

In JSON, object property names must be quoted.

// ❌ invalid JSON
    { a: 1 }

    // ✅ valid JSON
    { "a": 1 }

5) NaN / Infinity

JSON only supports finite numbers. Use null or a string if you need placeholders. 

// ❌ invalid JSON
    { "value": NaN }

    // ✅ valid JSON
    { "value": null }

6) Using the wrong top-level type

Some APIs expect an object, but you provided an array (or vice versa). That’s valid JSON, but it still may break your app.

Try it instantly

Paste your JSON into the formatter to see exact error locations: JSON Formatter.

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