JSON Trailing Comma Error Fix

JSON is stricter than JavaScript object literals. Trailing commas, comments and single-quoted strings can break API requests and config files.

Symptoms

  • JSON.parse fails with an unexpected token error.
  • API returns invalid JSON or bad request.
  • A config works in JavaScript but fails in a JSON parser.

Likely causes

  • Trailing comma after the last array or object item.
  • Comments inside JSON.
  • Single quotes or unquoted property names.

Fix steps

  1. Paste the payload into a JSON validator.
  2. Remove trailing commas and comments.
  3. Pretty format the valid result before sending it to an API.

Verify the fix

  • Validate JSON syntax.
  • Minify the output and compare it with the original payload.
  • Run the API request with a known-good cURL command.

FAQ

Are trailing commas allowed in JSON?

No. Some JavaScript contexts allow them, but JSON does not.

Can comments be used in JSON?

No. Use a different config format if comments are required.

Related tools and guides

JSON JSON Validator and Formatter

Validate JSON, format it for reading, or minify it for compact API payloads without sending data to an external API.

 OpenAI OpenAI API Request Checker

Statically inspect an OpenAI API request body for common JSON and parameter mistakes before sending it to the API.

 cURL cURL Command Builder

Build readable cURL commands for API requests with method, headers, JSON body and safe auth placeholders.

 OpenAI Debug OpenAI API Request JSON Before Sending

Most API request bugs are easier to fix before the request is sent. Start with valid JSON, then check model-family parameters and only then debug application code.

Last updated: May 18, 2026