What is a JSON formatter?

A JSON formatter (also called JSON beautifier or pretty printer) takes compact or messy JSON data and reformats it with proper indentation and line breaks, making it human-readable. It typically also validates the JSON to ensure it's syntactically correct. Our online JSON formatter adds syntax highlighting, error detection with line numbers, and one-click minify.

How do I format JSON online?

Paste your JSON into the formatter and it instantly formats with proper indentation. Choose 2-space, 4-space, or tab indentation. Click Minify to compress, or Copy to copy the formatted result. The formatter also highlights syntax errors with line numbers — fix the issue and re-format.

How do I validate JSON?

Our JSON formatter automatically validates as you type. If there's an error, it shows the message and position (line and column). Validation is per RFC 8259 / ECMA-404 — strict mode, no comments, no trailing commas, no single quotes, no unquoted keys.

What is the difference between JSON format and minify?

Formatting (pretty printing) adds indentation and line breaks to make JSON readable. Minifying removes all unnecessary whitespace to make it as compact as possible. Format for development and debugging; minify for production to reduce file size and network payload — typically 20–60% size reduction.

Why is my JSON invalid?

Common reasons: (1) Trailing commas: {"a":1,} — remove the last comma. (2) Single quotes: {'key':'value'} — use double quotes. (3) Unquoted keys: {key:"value"} — quote all keys. (4) Missing brackets or braces. (5) undefined or NaN values — use null instead. (6) Comments — JSON does not support // or /* */. The validator shows the exact line and column.

Can I format large JSON files?

Yes. The formatter handles large JSON files in the browser. For very large files (10MB+), formatting may take a moment. All processing is client-side — your data never leaves your browser, making this safe for sensitive payloads like API responses, JWTs, or user data.

What indentation should I use for JSON?

2 spaces is the most common (used by npm, prettier defaults, and most JavaScript projects). 4 spaces is preferred in some enterprise codebases for extra readability. Tabs are less common but supported. For production APIs and config-as-code, use minified JSON to save bandwidth.

What is RFC 8259 and how does it differ from older JSON specs?

RFC 8259 (2017) is the current IETF Internet Standard for JSON, replacing RFC 7159. Key requirements: UTF-8 encoding for network exchange, no BOM, top-level value can be any JSON value (not just object or array). ECMA-404 is the parallel JSON syntax standard. Our formatter validates per RFC 8259 strict mode.

What is JSON Schema and how do I validate against it?

JSON Schema (json-schema.org) is a vocabulary for describing the structure of JSON documents — required fields, value types, ranges, enums, and pattern constraints. You write a schema (itself JSON) and validate instances against it. Common implementations: Ajv (JavaScript), jsonschema (Python), JSON Schema Validator (Java). Schema validation catches semantic errors that pure JSON syntax checking misses.

What is JSONPath and how do I use it?

JSONPath is a query syntax for JSON, similar to XPath for XML. Use it to extract specific values: $.store.book[0].title selects the first book's title; $..price returns all price fields recursively; $.items[?(@.price < 10)] filters items by price. Supported in tools like jq (with slight syntax differences), Postman, and most API gateways.

What is JSON Lines (JSONL or NDJSON)?

JSON Lines (jsonlines.org) is a format where each line is a complete, valid JSON value. Used heavily for log streaming, ETL pipelines, and ML training data. Easy to append to, easy to read line-by-line in any language without loading the entire file. Common file extensions: .jsonl, .ndjson. Tools: jq -c, Python json.loads in a loop, BigQuery NDJSON ingest.

What is JSON5 and should I use it?

JSON5 (json5.org) extends JSON with comments, trailing commas, single quotes, unquoted keys, and other developer conveniences. It is NOT compatible with the standard JSON.parse — you need a JSON5 parser. Use JSON5 for human-edited config files (like babel.config.json5) but stick to strict JSON for APIs, data interchange, and storage.

How do I avoid JSON security vulnerabilities?

Three main risks: (1) Prototype pollution — never merge untrusted JSON into existing objects without sanitizing __proto__, constructor, prototype keys. (2) eval() on JSON — never use eval to parse JSON; use JSON.parse, which is sandboxed. (3) Re-serialization gotchas — JSON.stringify drops functions, undefined, and converts NaN/Infinity to null. Validate input against a JSON Schema before processing.

How do I convert JSON to YAML, CSV, or XML?

JSON ↔ YAML is the most lossless (both support nested objects/arrays). JSON → CSV requires flattening — works best for arrays of flat objects. JSON → XML is straightforward for trees but loses array vs object distinction. Tools: js-yaml or PyYAML for YAML; pandas or csvkit for CSV; xml-js or xmltodict for XML. Watch for type coercion (YAML auto-types yes/no/true/null) and field-name escaping (XML element names can't start with digits).

How do I diff two JSON files?

Sort keys recursively in both files first (JSON.stringify with replacer or jq --sort-keys), then run a standard diff. For semantic diffs that ignore key order and array reordering, use json-diff (npm), DeepDiff (Python), or Visual Studio Code's JSON-aware diff extension. For very large files, normalize to JSON Lines and use line-based diff.

Why does JSON.stringify drop my function or undefined value?

By design — JSON has no native types for functions, undefined, Symbol, or BigInt. JSON.stringify silently omits them in objects (and converts to null in arrays). Workarounds: convert to string explicitly, use a replacer function, or pick a richer format (BSON, MessagePack, CBOR) if you need those types preserved.

Can JSON have comments?

Standard JSON (RFC 8259, ECMA-404) does NOT support comments — // and /* */ are syntax errors. If you need comments in config files, use JSON5, JSONC (used by VS Code settings), or YAML. For pure data interchange, keep it strict and document elsewhere.

Is this JSON formatter safe for sensitive data?

Yes. Everything runs in your browser — JSON is parsed, formatted, validated, and minified entirely on your device. No data is uploaded, logged, or sent to any server. Safe for API keys, JWT payloads, customer data, and other sensitive JSON. You can verify by opening DevTools → Network and checking that no requests fire while you format.

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JSON Formatter

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Indent:

info Paste JSON to format

0 lines 0 B 0 keys depth 0

Input Values

JSON Input

lightbulb Tips

•JSON keys must use double quotes
•Trailing commas are not valid JSON
•Use 2-space indent for most projects
•Minify JSON for API payloads