Leading byte-order mark (BOM)

What it means

Some Windows editors (Notepad, PowerShell, Visual Studio) prepend an invisible byte-order mark (U+FEFF) when saving. Strict JSON does not allow it before the first value.

Example

\uFEFF{ "a": 1 }

{ "a": 1 }

How to fix it

Save the file as UTF-8 without BOM, or parse in JSONC mode where it is a warning.

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.