---

title: "\"Your 19-digit ID is a different number after JSON.parse\" "

published: false

description: "\"RFC 8259 puts no size limit on numbers. JavaScript has exactly one numeric type. What that costs, measured on Node 22.\" "

tags: javascript, json, webdev, api

canonical_url: https://www.shoulin.shop/guides/why-json-numbers-lose-precision

---

A support ticket I keep seeing, in various disguises: "the ID changed after we formatted the JSON." It didn't change because of the formatter. It changed the moment the document was parsed, before any tool could intervene.

Here is the whole failure in one line:

JSON . parse ( ' {"id":9007199254740993} ' ). id // 9007199254740992

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Nothing was malformed. The container was too small.

The spec allows it; the runtime does not

RFC 8259 does not put a size limit on numbers.…