[Home](./index.md) > [puppeteer](./puppeteer.md) > [Protocol](./puppeteer.protocol.md) > [Runtime](./puppeteer.protocol.runtime.md) > [CustomPreview](./puppeteer.protocol.runtime.custompreview.md) > [header](./puppeteer.protocol.runtime.custompreview.header.md) ## Protocol.Runtime.CustomPreview.header property The JSON-stringified result of formatter.header(object, config) call. It contains json ML array that represents RemoteObject. Signature: ```typescript header: string; ```