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JustDevTools
  • JSON formatter and validator
    Format, minify and validate JSON, with the exact line and column of any syntax error.
  • JWT decoder
    Read a JWT's header and payload, with issued-at and expiry times shown as real dates.
  • Base64 encoder and decoder
    Encode and decode Base64 and Base64URL, with full Unicode support.
  • JSON to TypeScript, Zod and Java
    Paste a JSON response and get TypeScript interfaces, a Zod schema or Java classes with Jackson annotations.
  • YAML to JSON converter
    Convert YAML to JSON and JSON to YAML, with the exact line of any syntax error. Handles multi-document files.
  • Regex tester
    Test JavaScript regular expressions with live match highlighting, capture groups and replace preview.
  • URL encoder and decoder
    Percent-encode and decode URLs and query values, and break a URL into its parts and parameters.
  • Unix timestamp converter
    Convert Unix timestamps in seconds or milliseconds to dates, and dates back to timestamps.
  • Cron expression explainer
    See what a cron expression means in plain English, what each field does and the next times it will run.
  • JSON to CSV converter
    Turn a JSON array into CSV for Excel or Google Sheets, or a CSV file into JSON. Nested objects become columns.
  • UUID generator and inspector
    Generate UUID v4 and time-ordered v7 in bulk, or paste a UUID to see its version and timestamp.
  • Text diff checker
    Compare two texts line by line and see exactly what was added, removed or changed.
  • Hash and HMAC generator
    SHA-256, SHA-1, SHA-384 and SHA-512 hashes and HMAC signatures of text, in hex or Base64.
  • Markdown previewer
    Write Markdown on the left and see it rendered live on the right, with GitHub-style tables and task lists.

JSON formatter and validator

Format, minify and validate JSON, with the exact line and column of any syntax error.

Runs locally. Nothing you paste leaves this tab.

Valid JSON. 84 B in, 129 B out.

Output

{
  "name": "Ada",
  "roles": [
    "admin",
    "dev"
  ],
  "active": true,
  "limits": {
    "rpm": 600,
    "burst": 20
  }
}

Format, minify and validate JSON

Paste JSON on the left and the formatted result appears on the right as you type. Switch to Minify to strip all whitespace before sending a payload or storing it. Turn on Sort keys to make two objects easier to compare.

Common JSON errors and how to fix them

When the input is invalid, the tool points to the exact line and column. These are the mistakes it catches most often:

Trailing commas

JavaScript allows a comma after the last item; JSON does not. {"a": 1,} fails, while {"a": 1} works.

Single quotes

Every string and every property name must use double quotes. {'a': 'b'} is valid JavaScript but not valid JSON.

Unquoted property names

{name: "Ada"} needs to be {"name": "Ada"}.

Line breaks inside strings

A raw line break inside a string is not allowed. Replace it with \n.

Comments, NaN and undefined

JSON has no comments and no NaN, Infinity or undefined. Use null for missing values.

Large numbers

JavaScript numbers lose precision above 253 − 1 (9007199254740991). If an API returns 64-bit IDs as numbers, formatting here may change their last digits, as it would in any JavaScript code. Ask the API for string IDs, or parse with a library that supports big integers.