Format, beautify, validate, and minify JSON data instantly. Runs formatting locally in your browser, precision error line highlighting, and alphabetized key sorting.
To format JSON, parse the serialized string into an in-memory syntax tree with 2-space, 4-space, or tab indentation while enforcing strict RFC 8259 compliance (double quotes, no trailing commas, valid brackets). DevOmniTools formats, diagnoses syntax errors, and minifies JSON 100% locally in browser memory for core formatting operations. Optional AI sends selected input after consent.
Top 5 most-searched JSON parse errors. Click "Try in Formatter" to load the broken JSON into the live validator above.
SyntaxError: Unexpected token in JSON at position 28JSON does not allow a comma after the last item in an object or array. JavaScript permits it, but RFC 8259 JSON does not.
{
"name": "Alice",
"role": "admin",
}{
"name": "Alice",
"role": "admin"
}Fix: Remove the trailing comma after the last key-value pair.
SyntaxError: Unexpected token in JSON — <!DOCTYPE received instead of JSONYour API endpoint returned an HTML error page (404/500) instead of JSON. JSON.parse receives the HTML DOCTYPE tag and immediately fails.
// API returned HTML, not JSON:
<!DOCTYPE html>
<html>
<body>404 Not Found</body>
</html>// Always check status before .json():
if (!res.ok) throw new Error(String(res.status));
const data = await res.json();Fix: Check response.ok before calling .json(). Never parse an HTML error page as JSON.
SyntaxError: Unexpected token in JSON at position 1JSON strictly requires double quotes for all keys and string values. Single quotes are JavaScript syntax — forbidden in RFC 8259.
{
'name': 'Alice',
'active': true
}{
"name": "Alice",
"active": true
}Fix: Replace all single quotes with double quotes for both keys and string values.
SyntaxError: Unexpected token in JSON at position 4JSON requires all object keys to be enclosed in double quotes. Unquoted keys are valid JavaScript but strictly forbidden in JSON.
{
name: "Alice",
age: 30
}{
"name": "Alice",
"age": 30
}Fix: Wrap every key name in double quotes.
SyntaxError: Unexpected token u in JSON at position 10JSON has no undefined or NaN. Valid JSON values are: null, true, false, numbers, strings, arrays, and objects only.
{
"name": "Alice",
"role": undefined,
"score": NaN
}{
"name": "Alice",
"role": null,
"score": null
}Fix: Replace undefined and NaN with null. JSON only supports: null, true, false, numbers, strings, arrays, objects.
Master JSON data structures, fix syntax errors instantly, and format payloads cleanly without sending data to remote servers.
JSON (JavaScript Object Notation) is the standard format for exchanging web data. It powers REST APIs, GraphQL services, microservices, and NoSQL databases like MongoDB.
In production environments, servers strip all spaces and line breaks to reduce payload size. While this speeds up network transfer, it makes the data impossible for humans to read or debug.
A reliable JSON formatter parses raw strings and restores clean, nested indentation. It also validates brackets, quotes, and commas to prevent silent crashes in your applications.
Raw Input: {"id":101,"name":"Alice","active":true} Formatted Output: { "id": 101, "name": "Alice", "active": true }
Step 1: Paste your raw JSON string into the input box on the left.
Step 2: Check the real-time validator. If there is a syntax error, the tool highlights the exact line and character.
Step 3: Click 'Format / Beautify' to apply clean indentation. Or click 'Minify' to compress the text onto one line.
Step 4: Click 'Copy Output' to copy the result, or click 'Download' to save a clean .json file to your computer.
1. Trailing Commas: JSON does not allow a comma after the last item. Change {"a": 1,} to {"a": 1}.
2. Single Quotes: JSON requires double quotes for all keys and strings. Change {'name': 'Alice'} to {"name": "Alice"}.
3. Unquoted Keys: Every key name must be inside double quotes. Change {name: "Alice"} to {"name": "Alice"}.
4. 64-bit Large Integers: DevOmniTools preserves large BigInt numbers (like 9007199254740993) without rounding errors.
• Webhook Debugging: Inspect minified JSON events from Stripe, GitHub, or Shopify webhooks.
• Configuration Files: Clean up package.json and cloud deployment manifests (note: tsconfig.json allows comments via JSONC, whereas strict RFC 8259 JSON parser will reject comments).
• Database Queries: Beautify exported records from PostgreSQL JSONB columns or MongoDB collections.
• Trailing Commas: Unlike JavaScript object literals, JSON strictly forbids trailing commas after the final array item or key-value pair. Example: {"item": 1,} will fail deserialization.
• Single vs. Double Quotes: All keys and string values in standard JSON must be enclosed in double quotes ("). Single quotes ('text') will throw an immediate parse error.
• Unquoted Numeric Keys: In JSON, object keys must always be strings. Expressions like {123: "data"} are invalid; they must be written as {"123": "data"}.
• Comment Inclusion: Pure RFC 8259 JSON does not support inline comments (// or /* */). Ensure all explanatory comments are removed prior to serializing payloads for external APIs.
When integrating distributed microservices and frontends, syntax crashes are frequent during unexpected network states. If your JavaScript or Node.js runtime throws `SyntaxError: Unexpected token < in JSON at position 0`, read our in-depth diagnostic guide on How to Fix Unexpected Token in JSON Errors to troubleshoot HTML 404/500 responses and UTF-8 BOM encodings.
To convert validated JSON payloads directly into strongly-typed TypeScript interfaces and nested models, inspect your schemas with our JSON to TypeScript Generator. To compare two JSON configuration dumps side-by-side and highlight structural deltas, run our visual Diff Checker.
Core tools process input locally. Optional AI sends the selected snippet through Cloudflare to Cloudflare AI or the optional Google Gemini fallback after consent; provider retention policies apply. Contact submissions send your details to our email provider. Offline use requires the page and its assets to finish caching; external AI and contact delivery require internet.
This error almost always occurs when your application calls response.json() on an API endpoint that returned an HTML error page (like a 404 or 500 starting with "<!DOCTYPE html>"), or when your file contains an invisible UTF-8 Byte Order Mark (BOM). Validate your API response status before parsing.
No. Under the official RFC 8259 standard, JSON strictly forbids single quotes (all strings and keys must use double quotes), trailing commas after the last element, and comments (// or /* */). Use our validator to instantly detect and highlight the exact line and position of these syntax errors so you can quickly correct them.
Backend serializers frequently serialize object keys in non-deterministic order, creating massive artificial Git diff churn. Alphabetizing keys stabilizes formatting across teams, making code reviews and configuration comparisons instant and clean.
The formatter enforces a safety limit. Practical capacity depends on available device memory and payload structure; split very large files before processing.
When JSON data is embedded inside another string or log export, quotes and special characters are often escaped (e.g. \"name\": \"value\"). To unescape JSON, paste the escaped string into DevOmniTools, remove outer string delimiters, and format it to parse the unescaped object into clean, formatted JSON.
Open your .json file in a text editor, then paste its contents into the formatter to validate syntax, format the text, sort keys, and download the cleaned result.
Offline use requires the page and its tool assets to finish caching first. Core transformations can then run locally; optional AI and contact delivery require internet.
Core tools are free to use without an account. Device memory and tool-specific safety limits apply. Optional AI and online contact services have usage limits.
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