JSON Tools & Developer Utilities
A complete suite of JSON utilities for developers. Format, validate, minify, compare, and convert JSON data.
JSON (JavaScript Object Notation) is the default data format for APIs, configuration files, and data exchange on the web. Almost every REST API, most databases, and countless config files use it. Working with JSON confidently — formatting, validating, comparing, and debugging — is a daily task for developers, data analysts, and anyone who interacts with web services.
This collection brings together the three JSON tools developers reach for most often. The JSON Formatter turns minified or malformed payloads into readable, indented structures. The JSON Validator checks syntax and pinpoints the exact line and character where errors occur. The JSON Diff compares two documents and highlights every structural and value difference.
Every tool runs entirely in your browser. Paste your JSON, get results instantly, and never worry about your data leaving your device. No sign-up, no uploads, no artificial size limits — documents up to several megabytes work reliably.
Tools in JSON Toolkit
3 tools in this collection.
JSON Formatter & Validator
Format, validate, and beautify JSON data instantly.
JSON Validator
Validate JSON with human-friendly error messages and instant feedback.
JSON Diff
Compare JSON files visually. Highlight additions, removals and modifications with side-by-side and inline comparison.
The JSON errors you will actually hit
Almost every JSON parse failure comes from the same short list, and nearly all of them are cases where valid JavaScript is not valid JSON. A trailing comma after the last item in an object or array is the most frequent — JavaScript tolerates it, JSON does not. Single-quoted strings are the second: JSON requires double quotes, for both keys and string values. Unquoted keys are the third; {name: "x"} is a JavaScript object literal, not JSON.
Then there are the values JSON simply has no concept of. undefined, NaN, and Infinity are all valid in JavaScript and all invalid in JSON, which is why JSON.stringify silently drops undefined properties rather than erroring. Comments are not permitted either, despite how often people try to add them to config files — that is what led to JSON5 and JSONC existing as separate formats.
Two subtler ones are worth knowing because they produce confusing errors. A byte-order mark at the start of a file — invisible in most editors, often introduced by Windows tooling — will fail parsing with an error pointing at position 0 that looks like nothing is wrong. And duplicate keys are technically permitted by the spec but handled inconsistently: most parsers keep the last occurrence and discard the earlier one silently, so data goes missing with no error at all.
How the three tools fit together
In practice you use them in sequence. When something breaks, the Validator goes first — it gives you a line and character position, which turns "this payload is broken somewhere" into a specific place to look. Formatting an invalid document does not help, because a formatter has to parse before it can indent.
Once the JSON parses, the Formatter is what makes it readable. A minified API response is technically complete and practically impossible to scan; indentation is what lets you see nesting depth, spot a null where you expected an object, and find the one field that is missing. Minify is the same tool in reverse, for when you want the smallest payload for transport.
The Diff is for the question the other two cannot answer: what actually changed. Comparing an API response before and after a deployment, checking whether a migration altered fields it should not have touched, or working out why staging and production behave differently. Reading two large JSON documents side by side manually is exactly the kind of task people are bad at and tools are good at.