JSON Stringify Online

JSON.stringify(value) converts a JavaScript value into its JSON text form. Objects become brace-wrapped key/value pairs, arrays become bracketed lists, strings are wrapped in double quotes with special characters escaped, and numbers, booleans and null pass through literally. The result is always a string — that is the point: text can travel where objects cannot, through HTTP bodies, localStorage, files and code.

The signature has two more arguments that are worth knowing. JSON.stringify(value, null, 2) is the pretty-print form every developer has typed at least once — the third argument sets two-space indentation, and it is the fastest debugger's tool for making a dense object readable. The second argument, the replacer, is a function (or an array of keys) that filters or transforms values during serialization: JSON.stringify(data, ["id", "name"]) emits only those two fields, which is a one-line way to strip payloads before logging them.

Four behaviors account for nearly every stringify bug report. First, undefined values, functions and Symbols vanish from objects silently — JSON.stringify({ a: 1, b: undefined }) produces {"a":1} with no error, which is why a missing field after a round-trip usually traces to an undefined property. Second, in arrays those same values become null instead of disappearing: [undefined] stringifies to [null].

Third, circular references throw a TypeError — an object that contains itself cannot be flattened into text, and the error message names the cycle rather than the path. Fourth, dates serialize through toJSON(): new Date("2026-10-25") becomes the ISO string "2026-10-25T00:00:00.000Z", which is why dates that go through stringify come back as strings and need reconstructing on the other side. Knowing these four turns mysterious data loss into a five-second diagnosis.

The three words overlap in search results because they describe different stages of the same pipeline. Stringify is the serialization: object to text. Minify is the presentation step on already-serialized text: strip insignificant whitespace, which stringify does by default. Escaping is the embedding step: taking that text and representing its quotes and newlines safely inside another string or document.

Practically: to ship JSON in an API response you stringify (which minifies by default). To embed that JSON inside another JSON string value, or inside an HTML attribute, you escape its quotes — JSON.stringify of a plain string does precisely that, wrapping the text in quotes and escaping every special character. The tool above covers the first two directly, and the examples below show the third.