Tools / JSON Formatter
JSON Formatter
Format, minify, and validate JSON right in your browser. Paste a blob, choose an indent, and get clean output — nothing is uploaded.
No valid JSON yet
// About this tool
JSON Formatter
This JSON formatter pretty-prints, minifies, and validates JSON entirely in your browser. Paste a blob, pick 1, 2, or 4-space indentation, and get clean, readable output you can copy straight back into your editor or a config file.
It also works as a validator: invalid JSON produces an error with the exact line and column, so you can find the stray comma or unquoted key without a round trip to a server.
Everything runs locally — your JSON is never uploaded, which makes the tool safe for configs, API responses, and payloads that contain sensitive values.
The workflow it's built for on this site: agent payloads. A tool call coming back from an MCP server, a model's function-call arguments, or a log line from a compromised agent usually arrives minified or half-escaped, and structure is the first thing you need when you're deciding whether it's safe to act on. Format it here first — the line-and-column error tells you immediately whether you're looking at JSON at all or at a truncated/wrapped variant — then run it through the JSON Schema Validator against the tool's declared schema before you let it execute. Formatter for readability, validator for the contract; both run client-side, which matters when the payload contains real secrets or un-disclosed tool arguments.
// When to use it
Format an API response for debugging
Paste a minified JSON response from curl or a browser and read it with proper indentation.
Read an agent's tool-call payload
Format the arguments a model produced before validating them against the tool's schema — structure first, contract second.
Validate a config file before committing
Catch a syntax error with its exact line and column before it breaks a pipeline.
// Questions
Is my JSON uploaded to a server?
No. Formatting, minifying, and validation all happen locally in your browser. Nothing is sent anywhere.
What indentation options are supported?
1, 2, or 4 spaces. You can switch between them at any time and the output updates instantly.
Does it support JSON5, comments, or trailing commas?
No — this is strict JSON only. Comments, unquoted keys, and trailing commas are reported as syntax errors, which is the behavior you want for validating standard JSON.
Can it format huge files?
There is no imposed limit because nothing is uploaded; practical limits depend on your browser's memory.
What's the difference between formatting and validating JSON?
Formatting changes presentation — indentation, whitespace, minification — and requires valid JSON to work. Validation checks the document parses and reports exactly where it doesn't, with line and column. This tool does both: paste something malformed and you get a validation error; paste something valid and you get clean output.
Why does my JSON fail with 'Unexpected token'?
The most common causes, in order: a trailing comma before a closing brace, single quotes instead of double quotes, an unquoted key, a trailing comma in an array, or a comment (// or /* */) — all legal in JavaScript but not in strict JSON. The error's line and column point at the first character the parser couldn't reconcile; check backwards from there for the actual mistake.
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