Lone surrogate in \u escape

What it means

Characters above U+FFFF are written as two \u escapes (a surrogate pair). A single, unpaired surrogate is technically accepted by JSON.parse, but the resulting string contains an invalid code unit that many systems will corrupt or reject.

Example

{ "emoji": "�" }

{ "emoji": "😀" }

How to fix it

Provide the full surrogate pair, or use the actual Unicode character.

Validate your JSON to see this and every other issue highlighted in one pass.

Diagnostics on this page come from @jsonlint/core, the open-source engine that powers the JSONLint validator. Install it with npm install @jsonlint/core.