diff --git a/package.json b/package.json
index ec6dee78d..a979e28f5 100644
--- a/package.json
+++ b/package.json
@@ -80,7 +80,7 @@
       "prefer-destructuring": "error",
       "unicorn/no-for-loop": "error",
       "unicorn/prefer-includes": "error",
-      "unicorn/prefer-string-slice": "warn",
+      "unicorn/prefer-string-slice": "error",
       "unicorn/filename-case": "warn",
       "unicorn/prefer-query-selector": "error"
     }
diff --git a/src/main/zapHomeFiles/hud/display.js b/src/main/zapHomeFiles/hud/display.js
index 3edb37065..8f9c65b3d 100644
--- a/src/main/zapHomeFiles/hud/display.js
+++ b/src/main/zapHomeFiles/hud/display.js
@@ -754,7 +754,7 @@ Vue.component('site-tree-node', {
 			if ((name.match(/\//g) || []).length > 2) {
 				// If there are more than 2 slashes just show last url element
 				// The first 2 slashes will be http(s)://...
-				name = name.substring(name.lastIndexOf('/') + 1);
+				name = name.slice(name.lastIndexOf('/') + 1);
 			}
 
 			if (isLeaf) {
diff --git a/src/main/zapHomeFiles/hud/target/inject.js b/src/main/zapHomeFiles/hud/target/inject.js
index 354ac5557..dcb2ee3a2 100644
--- a/src/main/zapHomeFiles/hud/target/inject.js
+++ b/src/main/zapHomeFiles/hud/target/inject.js
@@ -33,7 +33,7 @@ const injection = (function () {
 		const r = Math.floor(Math.random() * 1000);
 		const tabId = String(millis) + '-' + r;
 
-		return tabId.substring(6);
+		return tabId.slice(6);
 	}
 
 	/* TARGET INTERACTIONS */
@@ -623,8 +623,8 @@ const injection = (function () {
 		if (zapReplaceOffset > 0) {
 			// Hide the zapHudReplaceReq injected when resending a message in the browser
 			// But don't loose any fragment
-			const fragment = window.location.hash.substr(1);
-			let origUrl = window.location.href.substring(0, zapReplaceOffset - 1);
+			const fragment = window.location.hash.slice(1);
+			let origUrl = window.location.href.slice(0, zapReplaceOffset - 1);
 			if (fragment) {
 				origUrl += '#' + fragment;
 			}
diff --git a/src/main/zapHomeFiles/hud/tools/commonAlerts.js b/src/main/zapHomeFiles/hud/tools/commonAlerts.js
index 1a223084f..5ecdd593f 100644
--- a/src/main/zapHomeFiles/hud/tools/commonAlerts.js
+++ b/src/main/zapHomeFiles/hud/tools/commonAlerts.js
@@ -85,7 +85,7 @@ const CommonAlerts = (function () {
 				if (zapReplaceOffset > 0) {
 					// Strip off the string used for resending in the browser
 					// Will be preceded by ? or &
-					origTarget = origTarget.substring(0, zapReplaceOffset - 1);
+					origTarget = origTarget.slice(0, zapReplaceOffset - 1);
 				}
 
 				let target = origTarget;
diff --git a/src/main/zapHomeFiles/hud/tools/utils/alertUtils.js b/src/main/zapHomeFiles/hud/tools/utils/alertUtils.js
index 86eeb3b44..e87cb9e39 100644
--- a/src/main/zapHomeFiles/hud/tools/utils/alertUtils.js
+++ b/src/main/zapHomeFiles/hud/tools/utils/alertUtils.js
@@ -70,7 +70,7 @@ const alertUtils = (function () {
 
 				if (target.indexOf('?') > 0) {
 					// Remove any url params
-					target = target.substring(0, target.indexOf('?'));
+					target = target.slice(0, target.indexOf('?'));
 				}
 
 				return apiCallWithResponse('alert', 'view', 'alertsByRisk', {url: target, recurse: 'false'});
diff --git a/src/main/zapHomeFiles/hud/utils.js b/src/main/zapHomeFiles/hud/utils.js
index 61cfebcaf..2fe62014d 100644
--- a/src/main/zapHomeFiles/hud/utils.js
+++ b/src/main/zapHomeFiles/hud/utils.js
@@ -43,27 +43,27 @@ const utils = (function () {
 	function parseRequestHeader(headerText) {
 		const header = {};
 
-		header.method = headerText.substring(0, headerText.indexOf(' '));
-		headerText = headerText.substring(headerText.indexOf(' ') + 1);
+		header.method = headerText.slice(0, headerText.indexOf(' '));
+		headerText = headerText.slice(headerText.indexOf(' ') + 1);
 
-		header.uri = headerText.substring(0, headerText.indexOf(' '));
-		headerText = headerText.substring(headerText.indexOf(' ') + 1);
+		header.uri = headerText.slice(0, headerText.indexOf(' '));
+		headerText = headerText.slice(headerText.indexOf(' ') + 1);
 
-		header.version = headerText.substring(0, headerText.indexOf('\r'));
-		headerText = headerText.substring(headerText.indexOf('\n') + 1);
+		header.version = headerText.slice(0, headerText.indexOf('\r'));
+		headerText = headerText.slice(headerText.indexOf('\n') + 1);
 
 		header.fields = {};
 		while (headerText !== '') {
-			const field = headerText.substring(0, headerText.indexOf(':'));
-			headerText = headerText.substring(headerText.indexOf(':') + 2);
+			const field = headerText.slice(0, headerText.indexOf(':'));
+			headerText = headerText.slice(headerText.indexOf(':') + 2);
 			let value;
 
 			if (!headerText.includes('\n')) {
 				value = headerText;
 				headerText = '';
 			} else {
-				value = headerText.substring(0, headerText.indexOf('\n'));
-				headerText = headerText.substring(headerText.indexOf('\n') + 1);
+				value = headerText.slice(0, headerText.indexOf('\n'));
+				headerText = headerText.slice(headerText.indexOf('\n') + 1);
 			}
 
 			header.fields[field] = value;
@@ -78,22 +78,22 @@ const utils = (function () {
 	function parseResponseHeader(headerText) {
 		const header = {};
 
-		header.version = headerText.substring(0, headerText.indexOf(' '));
-		headerText = headerText.substring(headerText.indexOf(' ') + 1);
+		header.version = headerText.slice(0, headerText.indexOf(' '));
+		headerText = headerText.slice(headerText.indexOf(' ') + 1);
 
-		header.status = headerText.substring(0, headerText.indexOf(' '));
-		headerText = headerText.substring(headerText.indexOf(' ') + 1);
+		header.status = headerText.slice(0, headerText.indexOf(' '));
+		headerText = headerText.slice(headerText.indexOf(' ') + 1);
 
-		header.reason = headerText.substring(0, headerText.indexOf(' '));
-		headerText = headerText.substring(headerText.indexOf(' ') + 1);
+		header.reason = headerText.slice(0, headerText.indexOf(' '));
+		headerText = headerText.slice(headerText.indexOf(' ') + 1);
 
 		header.fields = {};
 		while (headerText !== '') {
-			const field = headerText.substring(0, headerText.indexOf(':'));
-			headerText = headerText.substring(headerText.indexOf(':') + 2);
+			const field = headerText.slice(0, headerText.indexOf(':'));
+			headerText = headerText.slice(headerText.indexOf(':') + 2);
 
-			const value = headerText.substring(0, headerText.indexOf('\n'));
-			headerText = headerText.substring(headerText.indexOf('\n') + 1);
+			const value = headerText.slice(0, headerText.indexOf('\n'));
+			headerText = headerText.slice(headerText.indexOf('\n') + 1);
 
 			header.fields[field] = value;
 		}
@@ -136,7 +136,7 @@ const utils = (function () {
 		let end = url.indexOf('&', start);
 		end = end === -1 ? url.length : end;
 
-		return url.substring(start, end);
+		return url.slice(start, end);
 	}
 
 	/* STORAGE */
@@ -650,7 +650,7 @@ const utils = (function () {
 					scheme = 'http';
 				}
 
-				return scheme + '://' + domain + url.substring(url.indexOf(domain) + domain.length);
+				return scheme + '://' + domain + url.slice(url.indexOf(domain) + domain.length);
 			})
 			.catch(errorHandler);
 	}
@@ -665,8 +665,8 @@ const utils = (function () {
 			// Construct the stack trace
 			const lines = error.stack.split('\n').slice(0, -1);
 			lines.forEach(line => {
-				const functionName = line.substring(0, line.indexOf('/'));
-				const urlAndLineNo = line.substring(line.indexOf('http'), line.length - 1);
+				const functionName = line.slice(0, line.indexOf('/'));
+				const urlAndLineNo = line.slice(line.indexOf('http'), -1);
 				const parts = urlAndLineNo.split(':');
 				let url = parts[0] + ':' + parts[1];
 				let lineNo = parts[2] + ':' + parts[3];