JSON Formatter — Pretty-print, Validate & Copy
How to Use
Type or paste JSON data into the textarea to see it automatically formatted. Choose between 2-space or 4-space indentation. If your JSON contains syntax errors, an error message will appear. Use the copy button to copy the formatted output to your clipboard.
What Is JSON
JSON (JavaScript Object Notation) is a lightweight data interchange format that is easy for humans to read and write, and easy for machines to parse and generate. It is widely used in web APIs, configuration files, and data storage. Pretty-printed JSON with proper indentation makes nested structures visually clear, which is invaluable for debugging and code review.
Use Cases
- Debugging API responses — pretty-print minified JSON to understand the structure at a glance
- Formatting config files — clean up package.json, tsconfig.json, and other configuration files
- Log analysis — expand single-line JSON log entries to inspect their contents
- Data validation — instantly detect JSON syntax errors and pinpoint the issue
Key Features
- Instant syntax error detection — catches missing brackets, extra commas, and other issues in real time
- Duplicate key warnings — alerts you when the same key appears twice in an object
- Indentation toggle — switch between 2-space and 4-space indentation with one click
- Large file support — handles big JSON payloads including BigInt values efficiently
Practical Tips
When inspecting API responses, paste them here first to get a clear picture of the structure. While this tool doesn't filter by key like jq, it's ideal for visual exploration of the full payload. Run your config files through the formatter before saving to catch syntax issues before they cause deployment failures.
Privacy
All JSON processing happens entirely in your browser. Your data is never sent to a server, stored, or logged. You can safely paste sensitive or proprietary data.
FAQ
What is the difference between JSON formatting and JSON Schema validation?
Formatting beautifies the structure and catches syntax errors, but does not validate the values themselves. JSON Schema is a separate specification for validating types, required fields, ranges, and more. This tool handles formatting and syntax checking only.
Is it safe to paste sensitive JSON like API keys or user data?
Yes. All formatting and validation happens entirely in your browser — there is no upload, no logging, and no storage. You can safely format JSON containing API keys, tokens, or personal information.
Can this tool handle large JSON files of several megabytes?
Yes, within your browser's memory and CPU limits. Files up to a few MB work smoothly. Beyond tens of MB you may see slowdowns or temporary browser unresponsiveness.
Does it support JSON with comments (JSONC) or JSON5?
No, currently only standard RFC 8259 JSON is supported. Comments and trailing commas will be reported as syntax errors. Pre-process VS Code-style config files before pasting if needed.
What does the duplicate key warning mean?
Standard JSON disallows duplicate keys within the same object. When detected, the tool warns you and keeps only the last value for that key in the formatted output, helping you spot accidental data loss.