diff --git a/.eslintrc.js b/.eslintrc.js
deleted file mode 100644
index ee4e4e4174..0000000000
--- a/.eslintrc.js
+++ /dev/null
@@ -1,17 +0,0 @@
-module.exports = {
-  env: {
-    browser: true,
-    es2021: true,
-    node: true
-  },
-  overrides: [
-  ],
-  parserOptions: {
-    ecmaVersion: 'latest',
-    sourceType: 'module'
-  },
-  rules: {
-    eqeqeq: 'off',
-    quotes: ['error', 'single' , { 'allowTemplateLiterals': true }]
-  }
-}
\ No newline at end of file
diff --git a/.github/workflows/eslint.yml b/.github/workflows/eslint.yml
new file mode 100644
index 0000000000..7d30697a21
--- /dev/null
+++ b/.github/workflows/eslint.yml
@@ -0,0 +1,24 @@
+name: ESLint
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  eslint:
+    name: Run ESLint
+    runs-on: ubuntu-latest
+    
+    steps:
+    - uses: actions/checkout@v4
+    - uses: actions/setup-node@v4
+      with:
+        node-version: '20'
+    
+    - name: Install dependencies
+      run: npm install
+      
+    - name: Run ESLint
+      run: npx eslint . --max-warnings=0
\ No newline at end of file
diff --git a/DEVELOPING.md b/DEVELOPING.md
index 712065ab46..0fc0e5cf94 100644
--- a/DEVELOPING.md
+++ b/DEVELOPING.md
@@ -36,6 +36,23 @@ ESBuild must also be used to compile the CSS supporting the MAPP and MAPP.UI ele
 
     npx esbuild --bundle public/css/_ui.css --outfile=public/css/ui.css --loader:.svg=dataurl
 
+## ESLint
+
+The codebase makes use of the [eslint](eslint.org) package to ensure that our code adhere to different rules and coding guidelines.
+To run `eslint` you will need to have the development packages installed. You can ensure they are installed by running `npm install` in the root of the xyz directory.
+
+To run the lint you can execute `npx eslint .` in the root of the application. This will show any issues there are with the codebase. You can also add the flag `--fix` to the command to allow eslint to fix any issues it may find.
+
+eslint command
+
+    npx esbuild .
+
+eslint command with fix
+
+    npx esbuild . --fix
+
+There are other extensions you can use in your editor to get on the fly error highlighting where any rules are broken. Please look into what eslint supports in your environment.
+
 ## version.js hash
 
 The mapp module object holds a hash of the latest release commit which can be generated by executing the version.js script in the root.
diff --git a/eslint.config.mjs b/eslint.config.mjs
new file mode 100644
index 0000000000..d5cb190633
--- /dev/null
+++ b/eslint.config.mjs
@@ -0,0 +1,22 @@
+export default [
+  {
+    ignores: ['public/js/lib/*', 'docs/**/*'],
+  },
+  {
+    files: ['**/*.js', '**/*.mjs'],
+    rules: {
+      quotes: ['error', 'single', { 'allowTemplateLiterals': true }],
+      'prefer-const': ['error', {
+        'destructuring': 'any',
+        'ignoreReadBeforeAssign': true
+      }],
+      'max-depth': ['error',
+        {
+          'max': 4
+        }
+      ],
+      // 'complexity': ['error', { 'max': 15 }],
+      'no-nested-ternary': 'error'
+    }
+  }
+];
\ No newline at end of file
diff --git a/lib/layer/decorate.mjs b/lib/layer/decorate.mjs
index 977a69c619..0dee92429d 100644
--- a/lib/layer/decorate.mjs
+++ b/lib/layer/decorate.mjs
@@ -236,7 +236,7 @@ async function zoomToExtent(params) {
   // Zooms to a specific extent.
 
   // XMLHttpRequest to layer extent endpoint
-  let response = await mapp.utils.xhr(`${this.mapview.host}/api/query/layer_extent?` +
+  const response = await mapp.utils.xhr(`${this.mapview.host}/api/query/layer_extent?` +
     mapp.utils.paramString({ // build query string for the url
       locale: this.mapview.locale.key,
       layer: this.key,
diff --git a/lib/layer/featureFields.mjs b/lib/layer/featureFields.mjs
index 866af75856..abac8a6c14 100644
--- a/lib/layer/featureFields.mjs
+++ b/lib/layer/featureFields.mjs
@@ -84,9 +84,9 @@ The jenks distribution method requires the stats.jenks utility method to calcula
 @param {layer} layer A decorated mapp layer object.
 */
 function jenks(layer) {
-  let theme = layer.style.theme;
+  const theme = layer.style.theme;
 
-  let n = Math.min(layer.featureFields[theme.field].values.length, theme.categories.length);
+  const n = Math.min(layer.featureFields[theme.field].values.length, theme.categories.length);
 
   // Parse array values as float.
   layer.featureFields[theme.field].values = layer.featureFields[theme.field].values.map(parseFloat);
@@ -113,7 +113,7 @@ The count distribution method counts values in the `featureFields.values[]` arra
 @param {layer} layer A decorated mapp layer object.
 */
 function count(layer) {
-  let theme = layer.style.theme;
+  const theme = layer.style.theme;
 
   layer.featureFields[theme.field].values.forEach(val => {
 
diff --git a/lib/layer/featureStyle.mjs b/lib/layer/featureStyle.mjs
index 4901fb5ed4..96ab042d2a 100644
--- a/lib/layer/featureStyle.mjs
+++ b/lib/layer/featureStyle.mjs
@@ -144,7 +144,7 @@ export default function featureStyle(layer) {
 
     if (!layer.style.cluster) return;
 
-    let clusterScale = parseFloat(layer.style.cluster.clusterScale)
+    const clusterScale = parseFloat(layer.style.cluster.clusterScale)
 
     // Spread cluster style into feature.style.
     feature.style = {
diff --git a/lib/layer/format/mvt.mjs b/lib/layer/format/mvt.mjs
index 429992eafe..5653916356 100644
--- a/lib/layer/format/mvt.mjs
+++ b/lib/layer/format/mvt.mjs
@@ -265,10 +265,10 @@ function changeEndLoad(layer) {
   const bounds = layer.mapview.getBounds()
 
   // Assign current viewport if queryparam is truthy.
-  let viewport = [bounds.west, bounds.south, bounds.east, bounds.north, layer.mapview.srid];
+  const viewport = [bounds.west, bounds.south, bounds.east, bounds.north, layer.mapview.srid];
 
   // Assign current viewport if queryparam is truthy.
-  let z = layer.mapview.Map.getView().getZoom();
+  const z = layer.mapview.Map.getView().getZoom();
 
   layer.xhr = new XMLHttpRequest()
 
diff --git a/lib/layer/themes/distributed.mjs b/lib/layer/themes/distributed.mjs
index ffcf28376c..1c04b91893 100644
--- a/lib/layer/themes/distributed.mjs
+++ b/lib/layer/themes/distributed.mjs
@@ -25,7 +25,7 @@ export default function(theme, feature) {
     theme.index = 0
   }
 
-  let field = theme.field || 'id'
+  const field = theme.field || 'id'
 
   // Get feature identifier for theme.
   const val = feature.properties[field]
diff --git a/lib/layer/themes/graduated.mjs b/lib/layer/themes/graduated.mjs
index 7c55464c8d..a87b555607 100644
--- a/lib/layer/themes/graduated.mjs
+++ b/lib/layer/themes/graduated.mjs
@@ -20,7 +20,7 @@ export default function (theme, feature) {
   // The graduated theme requires feature.properties.
   if (!feature.properties) return;
 
-  let catValue = Array.isArray(feature.properties.features) ?
+  const catValue = Array.isArray(feature.properties.features) ?
 
     // Reduce array of features to sum catValue
     feature.properties.features.reduce((total, F) => total + Number(F.getProperties()[theme.field]), 0) :
@@ -35,9 +35,9 @@ export default function (theme, feature) {
       'greater_than': val => cat => val >= cat.value
     }
 
-    let index = theme.categories.findIndex(graduated_breaks[theme.graduated_breaks](catValue))
+    const index = theme.categories.findIndex(graduated_breaks[theme.graduated_breaks](catValue))
 
-    let cat = theme.categories.at(index)
+    const cat = theme.categories.at(index)
 
     // Spread cat style to retain scale property
     feature.style = {
diff --git a/lib/location/create.mjs b/lib/location/create.mjs
index e08d784c71..3c660cda2b 100644
--- a/lib/location/create.mjs
+++ b/lib/location/create.mjs
@@ -80,7 +80,7 @@ export default async function createLocation(feature, interaction, layer) {
     setTimeout(checkFeature, 1000);
 
     function checkFeature() {
-      let found = layer.features?.find(F => F.properties?.id === location.id);
+      const found = layer.features?.find(F => F.properties?.id === location.id);
       if (found) {
         layer.source.un('tileloadend', concatFeatures);
       } else {
diff --git a/lib/mapp.mjs b/lib/mapp.mjs
index ee87300e1b..5672f7e261 100644
--- a/lib/mapp.mjs
+++ b/lib/mapp.mjs
@@ -57,7 +57,7 @@ if (window.ol === undefined) {
 
 } else {
 
-  let olVersion = parseFloat(ol?.util.VERSION)
+  const olVersion = parseFloat(ol?.util.VERSION)
 
   console.log(`OpenLayers version ${olVersion}`)
 
diff --git a/lib/plugins/login.mjs b/lib/plugins/login.mjs
index 46c242174d..71fad68643 100644
--- a/lib/plugins/login.mjs
+++ b/lib/plugins/login.mjs
@@ -25,6 +25,6 @@ export function login(plugin, mapview) {
   btnColumn.appendChild(mapp.utils.html.node`
     <a
       title=${mapp.user ? mapp.dictionary.toolbar_logout : mapp.dictionary.toolbar_login}
-      href=${mapp.user ? "?logout=true" : "?login=true"}>
+      href=${mapp.user ? '?logout=true' : '?login=true'}>
       <div class=${iconClass}>`);
 }
\ No newline at end of file
diff --git a/lib/ui/Gazetteer.mjs b/lib/ui/Gazetteer.mjs
index 0821770836..0922a327ac 100644
--- a/lib/ui/Gazetteer.mjs
+++ b/lib/ui/Gazetteer.mjs
@@ -42,7 +42,7 @@ export default gazetteer => {
     if (!e.target.value.length) return;
 
     // Get possible coordinates from input.
-    let ll = e.target.value.split(',').map(parseFloat)
+    const ll = e.target.value.split(',').map(parseFloat)
 
     // Check whether coordinates are valid float values.
     if (ll.length === 2 && ll.every(n => typeof n === 'number' && !isNaN(n) && isFinite(n))) {
diff --git a/lib/ui/elements/legendIcon.mjs b/lib/ui/elements/legendIcon.mjs
index 95e9436691..d101be39ee 100644
--- a/lib/ui/elements/legendIcon.mjs
+++ b/lib/ui/elements/legendIcon.mjs
@@ -72,7 +72,7 @@ function createIconFromArray(style) {
     });
   };
 
-  let legendScale = style.icon[0].legendScale || 1;
+  const legendScale = style.icon[0].legendScale || 1;
 
   style.icon.forEach((icon) => {
 
diff --git a/lib/ui/layers/filters.mjs b/lib/ui/layers/filters.mjs
index e9cf14a227..4f6b43ec5f 100644
--- a/lib/ui/layers/filters.mjs
+++ b/lib/ui/layers/filters.mjs
@@ -522,7 +522,7 @@ async function filter_in(layer, filter) {
 
         const pattern = e.target.value;
 
-        let filtered = filter[filter.type].filter(val =>
+        const filtered = filter[filter.type].filter(val =>
 
           // val may not be string.
           val.toString().toLowerCase().startsWith(pattern.toLowerCase()))
diff --git a/lib/ui/layers/legends/categorized.mjs b/lib/ui/layers/legends/categorized.mjs
index 743ebeb285..e01ba357c6 100644
--- a/lib/ui/layers/legends/categorized.mjs
+++ b/lib/ui/layers/legends/categorized.mjs
@@ -85,7 +85,7 @@ export default function categorizedTheme(layer) {
     const cat_label = cat.label + (cat.count? ` [${cat.count}]`:'')
 
     // Cat label with filter function.
-    let label = mapp.utils.html`<div
+    const label = mapp.utils.html`<div
       class=${classList}
       style="grid-column: 2;"
       onclick=${e => catToggle(e, layer, cat)}>${cat_label}`
diff --git a/lib/ui/locations/entries/cloudinary.mjs b/lib/ui/locations/entries/cloudinary.mjs
index 4283b9adc7..578f869802 100644
--- a/lib/ui/locations/entries/cloudinary.mjs
+++ b/lib/ui/locations/entries/cloudinary.mjs
@@ -186,10 +186,10 @@ function imageLoad(e, entry) {
 
   img.onload = async () => {
 
-    let
-      canvas = mapp.utils.html.node`<canvas>`,
-      max_size = 1024,
-      width = img.width,
+    const canvas = mapp.utils.html.node`<canvas>`
+    const max_size = 1024
+
+    let width = img.width,
       height = img.height
 
     // resize
@@ -276,7 +276,7 @@ async function docLoad(e, entry) {
 
 async function trash(e, entry) {
 
-  const confirm = await mapp.ui.elements.confirm({text: mapp.dictionary.remove_item_confirm});
+  const confirm = await mapp.ui.elements.confirm({ text: mapp.dictionary.remove_item_confirm });
 
   if (!confirm) return;
 
diff --git a/lib/utils/copyToClipboard.mjs b/lib/utils/copyToClipboard.mjs
index 9bac15f02e..cfd1a17fb0 100644
--- a/lib/utils/copyToClipboard.mjs
+++ b/lib/utils/copyToClipboard.mjs
@@ -7,7 +7,7 @@
 // Create temporary textarea to copy string to clipboard.
 export function copyToClipboard(str) {
 
-  let textArea = document.body.appendChild(mapp.utils.html.node`
+  const textArea = document.body.appendChild(mapp.utils.html.node`
     <textarea style="visibility=none;">`);
   
   textArea.value = str;
diff --git a/lib/utils/csvDownload.mjs b/lib/utils/csvDownload.mjs
index 29d61de642..137dc84382 100644
--- a/lib/utils/csvDownload.mjs
+++ b/lib/utils/csvDownload.mjs
@@ -16,7 +16,7 @@ export default function csvDownload(data, params = {}) {
 
   const rows = data.map(record => {
 
-    let row = Array.isArray(params.fields)
+    const row = Array.isArray(params.fields)
      ? fieldsFunction(record, params.fields)
      : Object.values(record)
      
@@ -64,7 +64,7 @@ function fieldsFunction(record, fields) {
     // Format number toLocaleString
     if (field.formatter === 'toLocaleString') {
 
-      let val = parseFloat(record[field.field])
+      const val = parseFloat(record[field.field])
 
       if (isNaN(val)) return;
 
diff --git a/lib/utils/dataURLtoBlob.mjs b/lib/utils/dataURLtoBlob.mjs
index cd4e495feb..1e7581ca83 100644
--- a/lib/utils/dataURLtoBlob.mjs
+++ b/lib/utils/dataURLtoBlob.mjs
@@ -7,7 +7,7 @@
 export function dataURLtoBlob(dataURL) {
 
   if (dataURL.indexOf(';base64,') == -1) {
-    let
+    const
       parts = dataURL.split(','),
       contentType = parts[0].split(':')[1],
       raw = parts[1];
@@ -15,7 +15,7 @@ export function dataURLtoBlob(dataURL) {
     return new Blob([raw], { type: contentType });
   }
   
-  let
+  const
     parts = dataURL.split(';base64,'),
     contentType = parts[0].split(':')[1],
     raw = window.atob(parts[1]),
diff --git a/lib/utils/merge.mjs b/lib/utils/merge.mjs
index fb55afde8c..736e834597 100644
--- a/lib/utils/merge.mjs
+++ b/lib/utils/merge.mjs
@@ -44,7 +44,7 @@ export default function mergeDeep(target, ...sources) {
 
     if (Object.getPrototypeOf(source) !== Object.getPrototypeOf({})) continue;
 
-    if (key === "__proto__" || key === "constructor") continue;
+    if (key === '__proto__' || key === 'constructor') continue;
 
     if (source[key] instanceof HTMLElement) {
       console.warn(source[key])
diff --git a/lib/utils/olStyle.mjs b/lib/utils/olStyle.mjs
index 5c75135a12..546c471adb 100644
--- a/lib/utils/olStyle.mjs
+++ b/lib/utils/olStyle.mjs
@@ -89,12 +89,12 @@ export default function olStyle(style, feature) {
     if (style.fillColor || style.strokeColor) {
 
       // Create OL fill.
-      let fill = style.fillColor && new ol.style.Fill({
+      const fill = style.fillColor && new ol.style.Fill({
         color: mapp.utils.hexa(style.fillColor, style.fillOpacity)
       })
 
       // Create OL stroke.
-      let stroke = style.strokeColor && new ol.style.Stroke({
+      const stroke = style.strokeColor && new ol.style.Stroke({
         color: mapp.utils.hexa(style.strokeColor, style.strokeOpacity),
         width: parseFloat(style.strokeWidth || 1)
       })
diff --git a/lib/utils/polygonIntersectFeatures.mjs b/lib/utils/polygonIntersectFeatures.mjs
index a5ad2055d6..bd5428823e 100644
--- a/lib/utils/polygonIntersectFeatures.mjs
+++ b/lib/utils/polygonIntersectFeatures.mjs
@@ -23,7 +23,7 @@ export function polygonIntersectFeatures(params) {
   }
 
   // Config for mapview draw interaction.
-  let interaction = {
+  const interaction = {
 
     // Draw polygon.
     type: 'Polygon',
diff --git a/lib/utils/svgSymbols.mjs b/lib/utils/svgSymbols.mjs
index 5cb5fce9ac..48f6876e88 100644
--- a/lib/utils/svgSymbols.mjs
+++ b/lib/utils/svgSymbols.mjs
@@ -14,7 +14,7 @@ const memoizedIcons = {
 
 export function dot(style) {
 
-  let lookup = Object.values({
+  const lookup = Object.values({
     fillColor: style.fillColor
   }).reduce((a, b) => a + b)
   
@@ -71,7 +71,7 @@ export function triangle(style) {
       return 16 + (val - 16) * scale
     }
 
-    let points = `${x(12, layer[0])},${y(4.68, layer[0])} ${x(2, layer[0])}, ${y(22, layer[0])} ${x(22, layer[0])}, ${y(22, layer[0])}`
+    const points = `${x(12, layer[0])},${y(4.68, layer[0])} ${x(2, layer[0])}, ${y(22, layer[0])} ${x(22, layer[0])}, ${y(22, layer[0])}`
 
     icon.appendChild(svg.node`
       <polygon
@@ -123,7 +123,7 @@ export function diamond(style) {
 
   style.layers && Object.entries(style.layers).forEach(layer => {
     
-    let points = `${s(12, layer[0])} ${s(0, layer[0])},${s(24, layer[0])} ${s(12, layer[0])},${s(12, layer[0])} ${s(24, layer[0])}, ${s(0, layer[0])} ${s(12, layer[0])}`
+    const points = `${s(12, layer[0])} ${s(0, layer[0])},${s(24, layer[0])} ${s(12, layer[0])},${s(12, layer[0])} ${s(24, layer[0])}, ${s(0, layer[0])} ${s(12, layer[0])}`
 
     icon.appendChild(svg.node`
       <polygon
diff --git a/lib/utils/verticeGeoms.mjs b/lib/utils/verticeGeoms.mjs
index 0ae4128e67..b73870a97d 100644
--- a/lib/utils/verticeGeoms.mjs
+++ b/lib/utils/verticeGeoms.mjs
@@ -12,7 +12,7 @@ export default feature => {
 
   let coords = geometry.getCoordinates()
 
-  let depth = getDepth(coords)
+  const depth = getDepth(coords)
 
   // Line string will have a depth of 2.
   if (depth === 2) {
diff --git a/mod/query.js b/mod/query.js
index 683547ca08..7fbcb78092 100644
--- a/mod/query.js
+++ b/mod/query.js
@@ -346,7 +346,7 @@ async function executeQuery(req, res, template, query) {
   }
 
   // Run the query
-  let rows = await dbs_connections[dbs](
+  const rows = await dbs_connections[dbs](
     query,
     req.params.SQL,
     req.params.statement_timeout || template.statement_timeout);
diff --git a/mod/user/acl.js b/mod/user/acl.js
index 1fbbc4c4b7..730afa68ad 100644
--- a/mod/user/acl.js
+++ b/mod/user/acl.js
@@ -12,43 +12,46 @@ const { Pool } = require('pg');
 
 const connection = process.env.PRIVATE?.split('|') || process.env.PUBLIC?.split('|')
 
-// The acl module will export an empty require object instead of a function if no ACL connection has been defined.
-if(!connection || !connection[1]) return;
-
-const acl_table = connection[1].split('.').pop()
+const acl_table = connection[1]?.split('.').pop()
 
-const acl_schema = connection[1].split('.')[0] === acl_table ? 'public' : connection[1].split('.')[0]
+const acl_schema = connection[1]?.split('.')[0] === acl_table ? 'public' : connection[1]?.split('.')[0]
 
 const pool = new Pool({
   connectionString: connection[0]
 })
 
-/**
-@function acl
-
-@description
-The acl method will connect to pg pool and query the ACL with a provided query template. The `/acl_table/` and `/acl_schema/` in the query template will be replaced with values provided as `PRIVATE` or `PUBLIC` environment variable.
-
-@param {string} q 
-Query template.
-@param {array} arr 
-Parameters to be substrituted in query template.
-*/
-
-module.exports = async function acl(q, arr) {
-
-  try {
-
-    const client = await pool.connect()
-
-    const { rows } = await client.query(q.replace(/acl_table/g, acl_table).replace(/acl_schema/g, acl_schema), arr)
-
-    client.release()
-
-    return rows
-
-  } catch (err) {
-    console.error(err)
-    return err
+// The acl module will export an empty require object instead of a function if no ACL connection has been defined.
+if (!connection?.[1]) {
+  module.exports = {};
+}
+else {
+  /**
+  @function acl
+  
+  @description
+  The acl method will connect to pg pool and query the ACL with a provided query template. The `/acl_table/` and `/acl_schema/` in the query template will be replaced with values provided as `PRIVATE` or `PUBLIC` environment variable.
+  
+  @param {string} q 
+  Query template.
+  @param {array} arr 
+  Parameters to be substrituted in query template.
+  */
+
+  module.exports = async function acl(q, arr) {
+
+    try {
+
+      const client = await pool.connect()
+
+      const { rows } = await client.query(q.replace(/acl_table/g, acl_table).replace(/acl_schema/g, acl_schema), arr)
+
+      client.release()
+
+      return rows
+
+    } catch (err) {
+      console.error(err)
+      return err
+    }
   }
 }
\ No newline at end of file
diff --git a/mod/user/cookie.js b/mod/user/cookie.js
index bdfdffe811..c756428058 100644
--- a/mod/user/cookie.js
+++ b/mod/user/cookie.js
@@ -74,7 +74,7 @@ module.exports = async function cookie(req, res) {
       if (err) return err
 
       // Get updated user credentials from ACL
-      let rows = await acl(`
+      const rows = await acl(`
         SELECT email, admin, language, roles, blocked
         FROM acl_schema.acl_table
         WHERE lower(email) = lower($1);`, [payload.email])
diff --git a/mod/user/fromACL.js b/mod/user/fromACL.js
index df89f63c0d..9eb2840e63 100644
--- a/mod/user/fromACL.js
+++ b/mod/user/fromACL.js
@@ -57,7 +57,7 @@ module.exports = async function fromACL(req) {
 
   if (req.headers.authorization) {
 
-    const user_string = Buffer.from(req.headers.authorization.split(" ")[1], 'base64').toString()
+    const user_string = Buffer.from(req.headers.authorization.split(' ')[1], 'base64').toString()
 
     const email_password = user_string.split(':')
 
diff --git a/mod/user/saml.js b/mod/user/saml.js
index b01d932cf4..ad04f3cb8a 100644
--- a/mod/user/saml.js
+++ b/mod/user/saml.js
@@ -197,7 +197,7 @@ async function acl_lookup(email) {
   const date = new Date()
 
   // Update access_log and return user record matched by email.
-  let rows = await acl(`
+  const rows = await acl(`
     UPDATE acl_schema.acl_table
     SET access_log = array_append(access_log, '${date.toISOString().replace(/\..*/,'')}')
     WHERE lower(email) = lower($1)
diff --git a/mod/utils/roles.js b/mod/utils/roles.js
index 49412cf955..a6ec2fa1fd 100644
--- a/mod/utils/roles.js
+++ b/mod/utils/roles.js
@@ -21,7 +21,7 @@ function check(obj, user_roles) {
 
   // Some negated role is included in user_roles[]
   const someNegatedRole = Object.keys(obj.roles).some(
-    (role) => /^!/.exec(role) && user_roles.includes(role.replace(/^!/, ""))
+    (role) => /^!/.exec(role) && user_roles.includes(role.replace(/^!/, ''))
   );
 
   if (someNegatedRole) return false;
diff --git a/mod/utils/sqlFilter.js b/mod/utils/sqlFilter.js
index 9b75c3fb23..a0263d6c06 100644
--- a/mod/utils/sqlFilter.js
+++ b/mod/utils/sqlFilter.js
@@ -110,7 +110,7 @@ function mapFilterEntries(filter) {
 
   if (Object.keys(filter).some(key => !SQLvalidation.test(key))) {
 
-    let unvalidatedKey = Object.keys(filter).find(key => !SQLvalidation.test(key))
+    const unvalidatedKey = Object.keys(filter).find(key => !SQLvalidation.test(key))
 
     console.warn(`"${unvalidatedKey}" field didn't pass SQL parameter validation`)
     return;
diff --git a/mod/workspace/_workspace.js b/mod/workspace/_workspace.js
index 9b77efa480..dceb986c13 100644
--- a/mod/workspace/_workspace.js
+++ b/mod/workspace/_workspace.js
@@ -102,7 +102,7 @@ async function layer(req, res) {
     req.params.user.roles.push('*')
   }
 
-  let layer = await getLayer(req.params)
+  const layer = await getLayer(req.params)
 
   if (layer instanceof Error) {
     return res.status(400).send(layer.message)
@@ -172,7 +172,7 @@ async function locale(req, res) {
     req.params.user.roles.push('*')
   }
 
-  let locale = await getLocale(req.params)
+  const locale = await getLocale(req.params)
 
   if (locale instanceof Error) {
     return res.status(400).send(locale.message)
diff --git a/mod/workspace/cache.js b/mod/workspace/cache.js
index 365a54d9f4..813ac1a2d0 100644
--- a/mod/workspace/cache.js
+++ b/mod/workspace/cache.js
@@ -89,10 +89,8 @@ The workspace is assigned to the module scope cache variable and the timestamp i
 */
 async function cacheWorkspace() {
 
-  let workspace;
-
   // Get workspace from source.
-  workspace = Object.hasOwn(getFrom, workspace_src) ?
+  const workspace = Object.hasOwn(getFrom, workspace_src) ?
     await getFrom[workspace_src](process.env.WORKSPACE) : {}
 
   // Return error if source failed.
diff --git a/mod/workspace/getTemplate.js b/mod/workspace/getTemplate.js
index 58c3d86c8b..76d4cfafe4 100644
--- a/mod/workspace/getTemplate.js
+++ b/mod/workspace/getTemplate.js
@@ -67,8 +67,6 @@ module.exports = async function getTemplate(template) {
     return template
   }
 
-  let response;
-
   if (template.cached) {
     return structuredClone(template.cached)
   }
@@ -85,7 +83,7 @@ module.exports = async function getTemplate(template) {
     return template
   }
 
-  response = await getFrom[method](template.src)
+  const response = await getFrom[method](template.src)
 
   if (response instanceof Error) {
 
diff --git a/mod/workspace/templates/location_update.js b/mod/workspace/templates/location_update.js
index 36817f8e69..5b56f4a1ba 100644
--- a/mod/workspace/templates/location_update.js
+++ b/mod/workspace/templates/location_update.js
@@ -36,7 +36,7 @@ module.exports = _ => {
 
         const jsonb_field = Object.keys(jsonb)[0]
 
-        let updateObject = []
+        const updateObject = []
         Object.keys(jsonb[jsonb_field]).forEach(key => {
           let value = typeof jsonb[jsonb_field][key] === 'string' ? `"${jsonb[jsonb_field][key]}"` : jsonb[jsonb_field][key]
 
diff --git a/mod/workspace/templates/mvt.js b/mod/workspace/templates/mvt.js
index faa507f0f3..cc116819c9 100644
--- a/mod/workspace/templates/mvt.js
+++ b/mod/workspace/templates/mvt.js
@@ -9,7 +9,7 @@ module.exports = _ => {
   // Push label (cluster) into fields
   _.label && fields.push(`${_.workspace.templates[_.label]?.template || _.label} AS ${_.label}`)
 
-  let
+  const
     x = parseInt(_.x),
     y = parseInt(_.y),
     z = parseInt(_.z)
diff --git a/mod/workspace/templates/mvt_geom.js b/mod/workspace/templates/mvt_geom.js
index b32f7839b5..0467aa3936 100644
--- a/mod/workspace/templates/mvt_geom.js
+++ b/mod/workspace/templates/mvt_geom.js
@@ -1,6 +1,6 @@
 module.exports = _ => {
 
-  let
+  const
     x = parseInt(_.x),
     y = parseInt(_.y),
     z = parseInt(_.z)
diff --git a/package.json b/package.json
index 8938ba04c3..c4dcbb44b3 100644
--- a/package.json
+++ b/package.json
@@ -29,17 +29,14 @@
     "simple-statistics": "^7.8.3"
   },
   "devDependencies": {
+    "@eslint/js": "^9.13.0",
     "clean-jsdoc-theme": "^4.3.0",
     "codi-test-framework": "^0.0.33",
     "cookie-parser": "^1.4.5",
     "dotenv": "^16.4.5",
     "esbuild": "^0.19.11",
-    "eslint": "^8.29.0",
-    "eslint-config-standard": "^17.0.0",
-    "eslint-plugin-import": "^2.26.0",
-    "eslint-plugin-n": "^15.6.0",
-    "eslint-plugin-promise": "^6.1.1",
+    "eslint": "^9.13.0",
     "express": "^4.18.3",
     "uhtml": "^3.1.0"
   }
-}
\ No newline at end of file
+}
diff --git a/public/tests/_base.test.mjs b/public/tests/_base.test.mjs
index 308536f766..b0d0c56216 100644
--- a/public/tests/_base.test.mjs
+++ b/public/tests/_base.test.mjs
@@ -247,7 +247,7 @@ export async function base() {
             target: document.getElementById('tabview-divider'),
             resizeEvent: (e) => {
 
-                let pageY = (e.touches && e.touches[0].pageY) || e.pageY;
+                const pageY = (e.touches && e.touches[0].pageY) || e.pageY;
 
                 if (pageY < 0) return;
 
@@ -282,7 +282,7 @@ export async function base() {
 
                 // Put focus on the gazetteer if the locations tab is activated.
                 if (e.target.dataset.id === 'locations') {
-                    let gazetteerInput = document.getElementById('gazetteerInput')
+                    const gazetteerInput = document.getElementById('gazetteerInput')
                     gazetteerInput && window.innerWidth > 768 && gazetteerInput.focus()
                 }
             }
diff --git a/public/tests/layer.test.mjs b/public/tests/layer.test.mjs
index 2f028b9c7a..93207d2ffa 100644
--- a/public/tests/layer.test.mjs
+++ b/public/tests/layer.test.mjs
@@ -18,7 +18,7 @@ export async function layerTest(mapview) {
 
                 if (layer.dataviews) {
 
-                    for (let dataview in layer.dataview) {
+                    for (const dataview in layer.dataview) {
                         dataview.show();
                     }
                 }
diff --git a/tests/lib/ui/layers/filters.test.mjs b/tests/lib/ui/layers/filters.test.mjs
index bcbd1afc22..02afd79522 100644
--- a/tests/lib/ui/layers/filters.test.mjs
+++ b/tests/lib/ui/layers/filters.test.mjs
@@ -7,7 +7,7 @@ export async function filtersTest(mapview) {
     await codi.describe('UI Layers: Filters test', async () => {
 
         //Creating the filter to be used in other tests
-        let filter = {
+        const filter = {
             field: 'id',
             minmax_query: 'minmax_query'
         };
diff --git a/tests/lib/utils/queryParams.test.mjs b/tests/lib/utils/queryParams.test.mjs
index c8ce132fc4..d38765f0df 100644
--- a/tests/lib/utils/queryParams.test.mjs
+++ b/tests/lib/utils/queryParams.test.mjs
@@ -19,7 +19,7 @@ export async function queryParamsTest(mapview) {
             id: 6,
         });
 
-        let params = {
+        const params = {
             layer: location_layer,
             queryparams: {
                 layer: location_layer,
@@ -34,7 +34,7 @@ export async function queryParamsTest(mapview) {
          */
         await codi.it('Should return undefined with null queryparams', async () => {
 
-            let null_params = {};
+            const null_params = {};
             const formattedValue = mapp.utils.queryParams(null_params);
             codi.assertEqual(formattedValue, undefined, `We expect the value to equal undefined, we received ${formattedValue}`)
         });
diff --git a/tests/mod/workspace/_workspace.test.mjs b/tests/mod/workspace/_workspace.test.mjs
index a7bfa97ef1..00dcdeae8a 100644
--- a/tests/mod/workspace/_workspace.test.mjs
+++ b/tests/mod/workspace/_workspace.test.mjs
@@ -44,7 +44,7 @@ export async function workspaceTest(mapview) {
         });
 
         await codi.it('Workspace: Getting template_test_vanilla Layer', async () => {
-            let layer = await mapp.utils.xhr(`/test/api/workspace/layer?layer=template_test_vanilla`);
+            const layer = await mapp.utils.xhr(`/test/api/workspace/layer?layer=template_test_vanilla`);
             codi.assertEqual(layer.key, 'template_test_vanilla', 'Ensure that we get the template_test_vanilla layer from the API')
             codi.assertEqual(layer.infoj.length, 6, 'The infoj should always have 6 infoj entries')
             codi.assertTrue(!!layer.style, 'The layer needs to have a style object from another template')