JSON Formatter and Validator

Tools and Utilities • Digital and Web Utilities

Written by STEM Calculators Team Published December 29, 2025 Updated February 24, 2026

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JSON input

Tip: Use Fill example to load a valid sample (and a trailing-comma sample to test tolerant mode).

Indent

Output mode

Options

Sort keys Tolerant (allow trailing commas)

Strict mode follows RFC JSON (no trailing commas). Tolerant mode only removes trailing commas outside strings.

Load from file

Loads the file content into the input box (no upload to server).

The validator uses the browser’s JSON parser. If invalid, you’ll get the exact line/column and an inline highlight in the viewer below.

Ready

Waiting for input

Formatted JSON

Pretty output with your indent setting (and optional key sorting).

Minified JSON

Compact output (no spaces or line breaks).

Paste JSON and click Validate & Build output.

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JSON Formatter + Validator

This tool checks whether your input is valid JSON and, when it is valid, generates two clean outputs: a human-readable formatted version and a compact minified version. When the input is invalid, it shows a precise error location (line/column) plus an inline highlight in the viewer.

Standard: Strict mode follows the JSON specification (RFC JSON / RFC 8259 rules): JSON does not allow trailing commas, comments, or unquoted keys.

What counts as “valid JSON”

Objects use { } with "double-quoted" keys.
Arrays use [ ].
Allowed values: strings, numbers, true, false, null, objects, arrays.
No trailing commas in strict mode: [1,2,] and {"a":1,} are invalid.
No comments: // and /* ... */ are invalid in strict JSON.

How the calculator works

Read input text from the textarea (nothing is executed; it is treated as plain text).
Optional tolerant preprocessing (only if you enable it): the tool removes trailing commas that appear right before ] or }, while carefully ignoring commas inside quoted strings.
Parse JSON using the browser’s JSON parser: JSON.parse(...).
- If parsing succeeds → status becomes Valid.
- If parsing fails → status becomes Invalid and an error location is computed.
Optional key sorting (if enabled): object keys are sorted recursively (A→Z) to produce stable output. Arrays keep their original order.
Build outputs:
- Formatted: JSON.stringify(value, null, indent) with indent = 2 / 4 / tab.
- Minified: JSON.stringify(value) (no whitespace).
Compute stats: byte size before/after (UTF-8 when available) and a simple node count (objects, arrays, keys, and values).

Error location and inline highlight (the visualization)

When JSON parsing fails, the browser typically reports an error message that includes a character index (often written as “position N”). The calculator converts that index into a line and column by counting newlines. Then it:

Marks the line in the left gutter with a small red dot.
Highlights the exact character at the reported position.
Shows a snippet with a caret ^ pointing to the column.

Why “tolerant mode” still gives correct locations: if trailing commas are removed before parsing, the tool keeps a map from “cleaned text index” back to the original index, so the highlight points to the right place in your original input.

Inputs and outputs summary

Section	What you provide	What you get	Notes
JSON input	Paste JSON text	Validation result	Strict by default (RFC JSON rules).
Indent	2 / 4 / tab	Formatted output spacing	Only affects formatted output.
Sort keys	On / off	Stable object key order	Recursively sorts objects; arrays unchanged.
Output mode	Format / Minify	Preferred output emphasis	The tool still shows both boxes for convenience.
Tolerant	On / off	Accepts trailing commas	Only removes trailing commas outside strings (no comment support).
Stats	—	Bytes + node count	Helps compare “before/after” size impact.

Practical tips

If you see Invalid JSON, start by checking the highlighted character and the line above it.
If you paste JSON from JavaScript configs, try enabling Tolerant to handle trailing commas.
Use Sort keys when you want stable diffs in Git or consistent API examples.

Security note: The formatter never executes code. It only parses JSON text and prints JSON text.

Processing steps

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