If set to a filename, it will compare existing source file md5 signatures against those found in the file's json data. Your TinyPNG API key to use for requests options.sigFile If type is not object, string presumed (the API key) options.key Sets options described below from its properties. Returns Stream containing compressed images options Var tinypng = require( 'gulp-tinypng-extended') To run tests: npm test Example var gulp = require( 'gulp') Install with npm - In your project folder, run: npm install gulp-tinypng- extended