Example of a Zotero engines.json (for using it replace the paths by null or something else)

engines.json

[
	{
		"name": "CrossRef Lookup",
		"alias": "CrossRef",
		"icon": "file:///C:/Users/zumstein/AppData/Roaming/Mozilla/Firefox/Profiles/fo682pah.default/zotero/locate/CrossRef%20Lookup.gif",
		"_urlTemplate": "http://crossref.org/openurl?{z:openURL}&pid=zter:zter321",
		"description": "CrossRef Search Engine",
		"hidden": false,
		"_urlParams": [],
		"_urlNamespaces": {
			"z": "http://www.zotero.org/namespaces/openSearch#",
			"": "http://a9.com/-/spec/opensearch/1.1/"
		},
		"_iconSourceURI": "http://crossref.org/favicon.ico"
	},
	{
		"name": "Google Scholar Search",
		"alias": "Google Scholar",
		"icon": null,
		"_urlTemplate": "http://scholar.google.com/scholar?as_q=&as_epq={z:title}&as_occt=title&as_sauthors={rft:aufirst?}+{rft:aulast?}&as_ylo={z:year?}&as_yhi={z:year?}&as_sdt=1.&as_sdtp=on&as_sdtf=&as_sdts=22&",
		"description": "Google Scholar Search",
		"hidden": false,
		"_urlParams": [],
		"_urlNamespaces": {
			"rft": "info:ofi/fmt:kev:mtx:journal",
			"z": "http://www.zotero.org/namespaces/openSearch#",
			"": "http://a9.com/-/spec/opensearch/1.1/"
		},
		"_iconSourceURI": "http://scholar.google.com/favicon.ico"
	},
	{
		"name": "Mannheim University (Universität Mannheim) Lookup",
		"alias": "Mannheim University (Universität Mannheim) Lookup",
		"icon": null,
		"_urlTemplate": "http://sfx.bib.uni-mannheim.de:8080/sfx_local?{z:openURL}",
		"description": "Look up books on Mannheim University (Universität Mannheim)",
		"hidden": false,
		"_urlParams": [],
		"_method": "GET",
		"_urlNamespaces": {
			"z": "http://www.zotero.org/namespaces/openSearch#",
			"rft": "info:ofi/fmt:kev:mtx:book",
			"xmlns": "http://a9.com/-/spec/opensearch/1.1/"
		},
		"_iconSourceURI": ""
	},
	{
		"name": "DOAI",
		"alias": "DOAI",
		"icon": "file:///C:/Users/zumstein/AppData/Roaming/Mozilla/Firefox/Profiles/fo682pah.default/zotero/locate/DOAI.ico",
		"_urlTemplate": "http://doai.io/{z:DOI}",
		"description": "Digital Open Access Identifier Lookup",
		"hidden": false,
		"_urlParams": [],
		"_method": "GET",
		"_urlNamespaces": {
			"z": "http://www.zotero.org/namespaces/openSearch#",
			"xmlns": "http://a9.com/-/spec/opensearch/1.1/"
		},
		"_iconSourceURI": "http://dissem.in/favicon.ico"
	},
	{
		"name": "oaDOI",
		"alias": "oaDOI",
		"icon": "file:///C:/Users/zumstein/AppData/Roaming/Mozilla/Firefox/Profiles/fo682pah.default/zotero/locate/oaDOI.png",
		"_urlTemplate": "http://oadoi.org/{z:DOI}",
		"description": "Alternative Open Access DOI Resolver",
		"hidden": false,
		"_urlParams": [],
		"_method": "GET",
		"_urlNamespaces": {
			"z": "http://www.zotero.org/namespaces/openSearch#",
			"xmlns": "http://a9.com/-/spec/opensearch/1.1/"
		},
		"_iconSourceURI": "https://impactstory.org/static/img/favicon.ico"
	}
]

Nice,it is useful!