Why is my JSON invalid?

The usual causes are trailing commas, single quotes instead of double quotes, comments, and unquoted keys. The error message points to the first character the parser could not read.

Is there a size limit?

Only your browser memory. Files of several megabytes format in well under a second.

Everything runs in your browser. Nothing you paste or open is uploaded.

SANDBASE TOOLS

JSON formatter and validator

Paste JSON to pretty-print it with 2 or 4 spaces, minify it, sort its keys, or find exactly where it is broken.

RUNS IN YOUR BROWSERNOTHING UPLOADEDNO WATERMARK

InputResult

{
  "model": "openai/gpt-6-astra",
  "messages": [
    {
      "role": "user",
      "content": "Hello"
    }
  ],
  "stream": false
}

Valid JSON · 134 bytes

How to use it

Step 1: Paste JSON into the input.
Step 2: Choose Format, Minify or Sort keys.
Step 3: Copy the result, or fix the error at the line and column shown.

Frequently asked questions

Why is my JSON invalid?: The usual causes are trailing commas, single quotes instead of double quotes, comments, and unquoted keys. The error message points to the first character the parser could not read.
Is there a size limit?: Only your browser memory. Files of several megabytes format in well under a second.
Is my JSON uploaded?: Everything runs in your browser. Nothing you paste or open is uploaded.