Fix JSON parse errors: trailing commas, quotes, and other gotchas

If you are staring at an error like Unexpected token or Invalid JSON, it usually comes down to one of five problems.

Start here:

• Open the JSON Formatter.
• Paste the JSON that is failing.
• Fix the first error it points to; reformat and try again.

Valid JSON looks like a JavaScript object, but it is not the same thing.

JavaScript lets you do things JSON does not:

• Single quotes: 'ok' instead of "ok"
• Unquoted keys: { ok: true }
• Comments: // like this
• Trailing commas: { "a": 1, }

If you copy from a JS file, a config snippet, or a blog post, you often pick up one of those.

Use this table when you want the fastest path to valid JSON.

• Front-end debugging: Copying from console logs often pulls in single quotes and trailing commas. Run it through the formatter before dropping it into tests or fixtures.
• API responses: Some proxies return HTML error pages. If parsing fails and you see angle brackets, you received HTML, not JSON—check the status code first.
• Config files (VS Code, ESLint, tsconfig): .jsonc allows comments; strict JSON parsers do not. Strip comments before bundling or sending to an API.
• Analytics/events: Hidden characters from spreadsheets or chat exports are common. Normalize to plain text, then validate.
• Embedded JSON in HTML: If you copy from <script type="application/json">, watch for escaped characters. Validate after unescaping.

Trailing comma

Invalid JSON:

{
  "name": "Ada",
  "role": "admin",
}

Fix:

{
  "name": "Ada",
  "role": "admin"
}

Single quotes and unquoted keys

Invalid JSON:

{ user: 'maria', active: true }

Fix:

{ "user": "maria", "active": true }

Comments in the middle of JSON

Invalid JSON:

{
  "env": "prod",
  // turn on for debugging
  "debug": false
}

Fix:

{
  "env": "prod",
  "debug": false
}

• Format before commit: Enable format-on-save or a pre-commit hook; if formatting fails, you see the error early.
• Validate API fixtures: In tests, assert that JSON.parse succeeds on mocked or recorded payloads.
• Avoid string splicing: Build objects in code and JSON.stringify them; concatenation is where stray commas creep in.
• Keep comments out of production JSON: If you use comments locally, strip them or convert to a format that supports them before production.

• Are all keys and strings double-quoted?
• Any trailing commas left?
• Did you remove // and /* ... */ comments?
• Does it format cleanly in the JSON Formatter?
• If minified, does it still parse after using the JSON minifier?

1. Open the JSON Formatter.
2. Paste your JSON, even if it is minified.
3. Pick an indent size (2 or 4 spaces), then copy the formatted output.

If the input is invalid, fix the first issue, then try again. JSON problems often cascade, and the first syntax error is the root cause.

• If you are debugging an API response, format it first; then compare versions with the diff tool.
• If you need to ship smaller payloads, format to make it readable, then minify it with the JSON minifier.
• If you suspect invisible characters, paste into a plain text field first (or use a plain text converter) before parsing.

• Shrink formatted output for transport with the JSON minifier.
• Compare two payloads side by side with the diff tool.
• Decode Base64-wrapped JSON with the Base64 encoder/decoder.

Textavia's JSON formatter runs locally in your browser. Your pasted JSON is processed on your device, not uploaded to a server.