JSON Guide: Format, Validate, Minify & Fix Errors

What JSON is (quick)

JSON (JavaScript Object Notation) stores objects, arrays, strings, numbers, booleans, and null as plain text. APIs, configs, and many logs speak JSON because it maps cleanly to in-memory structures in most languages.

It is not JavaScript source code. Quotes, commas, and comments follow stricter rules than JS object literals — which is why “almost JSON” from the console often fails validators.

• Objects use { } with "double-quoted" keys.
• Arrays use [ ] with ordered values.
• No trailing commas, no // comments, no single-quoted strings.

Format (pretty-print) for debugging

Formatting adds indentation and newlines without changing values. Use it when reading API responses, reviewing fixtures, or preparing a visual comparison. Prefer 2-space indent for most web JSON.

Open SparkJSON’s formatter, paste, choose indent, then Format & Validate. Invalid input must be fixed before pretty-print succeeds.

Validate before you ship

Syntax validation asks whether the string is parseable JSON. It is not the same as JSON Schema (field types and required keys). Catch trailing commas, unquoted keys, and duplicate-key overwrites early.

SparkJSON reports the first failure with line and column, plus duplicate-key warnings when JSON.parse would silently keep the last value.

Minify for payloads and storage

Minifying removes insignificant whitespace so payloads are smaller on the wire. Round-trip: minify → format should restore readability without changing data. Don’t minify while you are still editing by hand.

Compare two documents

When two configs or API snapshots diverge, a structural JSON diff lists added, removed, and changed paths. Object key order does not matter; array index order does. Use SparkJSON’s compare tool after both sides parse cleanly.

Privacy when pasting secrets

Debugging often means pasting tokens, PII, or internal payloads. Prefer client-side tools and confirm in DevTools → Network that the paste does not POST to a server. SparkJSON has no backend for tool input by design.

Next deep-dives

Use the linked guides below for step-by-step tutorials, error catalogs, and format comparisons. Each page has its own FAQ and HowTo schema where applicable.

• How to format JSON online — indent choices and shortcuts.
• How to validate JSON — syntax vs schema.
• Common JSON errors — trailing commas, quotes, duplicates.
• JSON minify guide — when compression helps.
• JSON vs XML — picking a format for new APIs.