Minified input
{"name":"Ada","active":true}JSON Formatter & Validator Online
JSON workspace
Drop a .json or .txt file here
Input: 0 B
Output: 0 B
Saving: —
Private, local processing: input is session-only by default and disappears when this tab closes. “Remember input” stores it in this browser until you clear it or turn the option off. Files are never uploaded.
Strict RFC 8259
Output
Formatted or minified JSON will appear here…
Plain-text output for selection
Format or validate JSON to build the tree.
Repair preview
Your input changes only when you select Fix JSON.
Shortcuts: Ctrl/Cmd + Enter formats with 2 spaces; Ctrl/Cmd + Shift + M minifies. Formatting is lossless for number spellings and duplicate keys.
Advertisement
How to format and validate JSON
Paste text, load a local file, drop a file, or choose a sample. Select Validate JSON to check syntax, Format to add readable indentation, or Minify to remove insignificant whitespace. Valid input can also be inspected in the searchable Tree tab.
Validation reads every token against strict JSON grammar. If it finds an error, it reports a consistent diagnosis, exact line and column, selects the offending range, and suggests a safe next step. Repair Preview recognizes only carefully scoped JSON-like features and never changes input until you select Fix JSON.
Pretty print versus minify
Pretty printing makes nested objects and arrays easier to review. Minifying is useful for transfer or compact storage. Both modes preserve number spellings—including large integers—and duplicate keys instead of round-tripping through JavaScript’s Number and object types.
Formatted output
{
"name": "Ada",
"active": true
}Invalid input
{"name": "Ada",}Trailing comma before } at line 1, column 15.
Common JSON syntax errors
Frequent problems include single quotes, unquoted object keys, comments, trailing commas, missing commas or colons, mismatched closing brackets, invalid escapes or numbers, uppercase True/False/Null, and multiple root values. The repair preview can safely propose changes for comments, single-quoted strings, unquoted keys, and trailing commas; other errors need a manual decision.
When to sort object keys
Sorting keys can make configuration files and source-control diffs deterministic. It does not sort arrays. Object member order is not semantically significant in JSON, but some consuming systems display or process insertion order, so sort only when that change is appropriate.
JSON standards, fidelity, privacy, and limits
Strict validation follows RFC 8259: keys and strings require double quotes; comments and trailing commas are not allowed; true, false, and null are lowercase; numbers follow JSON number syntax; and the document contains one JSON value.
Syntax validation answers whether text is valid JSON. It does not perform JSON Schema validation, which checks whether valid JSON has required fields, types, ranges, or other application rules.
Formatting and minifying preserve raw number tokens and duplicate keys. Warnings flag integers outside ±9,007,199,254,740,991 because other JavaScript software may round them, and duplicate keys because many parsers silently keep only the last value. Sorting keys deliberately changes object member order.
All work happens locally. Browser memory is the practical file-size limit; Tree view creates extra page elements and is best avoided for very large documents. Session input lasts until the tab closes, while remembered input lasts in local browser storage until Clear is selected or remembering is disabled.
Explanatory content last reviewed: .
JSON formatter and validator FAQ
How do I validate JSON?
Paste, type, or load JSON, then select Validate JSON. The tool checks strict RFC 8259 syntax and reports the exact line and column of the first error.
Why is my JSON invalid?
Common causes include single-quoted strings, unquoted keys, trailing commas, comments, missing commas or colons, mismatched brackets, invalid numbers, uppercase literals, and more than one root value.
How do I locate a JSON parse error?
The result identifies the error type, line, column, and character range. The editor selects that range and scrolls the offending line into view when you run validation.
Are comments or trailing commas allowed in JSON?
No. Strict RFC 8259 JSON allows neither comments nor trailing commas. Repair Preview can propose removing them, but only Fix JSON changes your input.
How is JSON different from a JavaScript object?
JSON is a text data format with stricter syntax. Keys and strings use double quotes, comments and trailing commas are forbidden, and values cannot be undefined, functions, NaN, or Infinity.
What is the difference between formatting and minifying JSON?
Formatting adds indentation and line breaks for reading; minifying removes insignificant whitespace for compact transfer or storage. Neither operation changes valid JSON values in this tool.
Can this tool handle large JSON files?
Processing happens in browser memory, so the practical limit depends on your device and browser. For very large files, close other tabs, avoid Tree view, and consider a streaming desktop tool.
Will large integers lose precision?
No during formatting or minifying: number tokens are preserved as text. The tool warns about integers outside JavaScript’s safe range because software that later parses them as Number may round them.
What happens to duplicate object keys?
The tool detects and warns about duplicate keys while preserving them in text output. Many parsers keep only the last value, so rename or remove duplicates before using the data.
Are loaded files uploaded?
No. Files are read locally by your browser and are never uploaded by this tool. Only .json and .txt files are accepted.
Is my JSON stored?
By default, input is kept only for this browser tab and removed when the tab closes. If you enable Remember input on this device, it stays in this browser’s local storage until you select Clear or disable the option. Nothing is sent to a server.