diff --git a/.dockerignore b/.dockerignore
index 284b069..7d55e2b 100644
--- a/.dockerignore
+++ b/.dockerignore
@@ -1,3 +1,4 @@
+.eslintcache
 .git
 dist
 node_modules
diff --git a/.eslintrc.yml b/.eslintrc.yml
deleted file mode 100644
index b85eb56..0000000
--- a/.eslintrc.yml
+++ /dev/null
@@ -1,6 +0,0 @@
-extends: seegno
-
-rules:
-  complexity: [2, 12]
-  id-length: 0
-  no-sync: 0
diff --git a/.gitignore b/.gitignore
index 3c3629e..7186998 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
+.eslintcache
 node_modules
diff --git a/.jscsrc b/.jscsrc
deleted file mode 100644
index 872495e..0000000
--- a/.jscsrc
+++ /dev/null
@@ -1,4 +0,0 @@
-plugins:
-  - jscs-config-seegno
-
-preset: seegno
diff --git a/eslint.config.mjs b/eslint.config.mjs
new file mode 100644
index 0000000..d5ed481
--- /dev/null
+++ b/eslint.config.mjs
@@ -0,0 +1,34 @@
+/**
+ * Module dependencies.
+ */
+
+import { defineConfig } from 'eslint/config';
+import uphold, { mocha as upholdMochaConfig } from 'eslint-config-uphold';
+
+/**
+ * `ESLint` configuration.
+ */
+
+export default defineConfig([
+  uphold,
+  { ignores: ['dist/**'] },
+  {
+    files: ['**/*.js'],
+    name: 'uk-modulus-checking/config',
+    rules: {
+      // Weight table columns are named after single letters in the VocaLink specification.
+      'id-length': 'off',
+      // Data sets are read from disk once, on instantiation.
+      'n/no-sync': 'off'
+    }
+  },
+  {
+    extends: [upholdMochaConfig],
+    files: ['test/**/*.js'],
+    name: 'uk-modulus-checking/tests',
+    rules: {
+      // Test cases are generated from the VocaLink account number fixtures.
+      'mocha/no-setup-in-describe': 'off'
+    }
+  }
+]);
diff --git a/package.json b/package.json
index 901793c..52adedf 100644
--- a/package.json
+++ b/package.json
@@ -19,7 +19,7 @@
   },
   "scripts": {
     "changelog": "github_changelog_generator --no-issues --header-label='# Changelog'",
-    "lint": "eslint src test && jscs src test",
+    "lint": "eslint --cache src test",
     "prepublish": "npm run transpile",
     "testdocker": "docker-compose run --rm sut",
     "test": "mocha $npm_package_options_mocha",
@@ -28,18 +28,16 @@
   },
   "devDependencies": {
     "babel-cli": "^6.4.0",
-    "babel-eslint": "^4.1.6",
     "babel-plugin-add-module-exports": "^0.1.2",
     "babel-plugin-static-fs": "^1.2.0",
     "babel-preset-es2015": "6.5.0",
     "babel-register": "^6.3.13",
-    "eslint": "^1.10.3",
-    "eslint-config-seegno": "2.0.0",
-    "eslint-plugin-babel": "^3.0.0",
-    "jscs": "^2.7.0",
-    "jscs-config-seegno": "^1.0.0",
+    "eslint": "~10.6.0",
+    "eslint-config-uphold": "^7.0.0",
+    "eslint-plugin-mocha": "^11.3.0",
     "mocha": "^2.3.4",
     "pre-commit": "^1.1.2",
+    "prettier": "^3.9.4",
     "should": "^8.0.0"
   },
   "pre-commit": [
diff --git a/src/constants.js b/src/constants.js
index f05556d..61729a0 100644
--- a/src/constants.js
+++ b/src/constants.js
@@ -1,5 +1,8 @@
+/**
+ * Exports.
+ */
 
-/* jscs:disable validateOrderInObjectKeys */
+/* eslint-disable sort-keys-fix/sort-keys-fix */
 export const positions = {
   u: 0,
   v: 1,
@@ -16,4 +19,4 @@ export const positions = {
   g: 12,
   h: 13
 };
-/* jscs:enable validateOrderInObjectKeys */
+/* eslint-enable sort-keys-fix/sort-keys-fix */
diff --git a/src/index.js b/src/index.js
index 8ecc904..0dd3cbd 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,4 +1,3 @@
-
 /**
  * Module dependencies.
  */
@@ -12,7 +11,6 @@ import path from 'path';
  */
 
 export default class UkModulusChecking {
-
   /**
    * Constructor.
    */
@@ -48,12 +46,27 @@ export default class UkModulusChecking {
     if (check.exception === 10) {
       const ab = number.charAt(positions.a) + number.charAt(positions.b);
 
-      if (ab === '09' || ab === '99' && this.pickPosition(number, 'b') === 9) {
+      if (ab === '09' || (ab === '99' && this.pickPosition(number, 'b') === 9)) {
         return [0, 0, 0, 0, 0, 0, 0, 0, check.c, check.d, check.e, check.f, check.g, check.h];
       }
     }
 
-    return [check.u, check.v, check.w, check.x, check.y, check.z, check.a, check.b, check.c, check.d, check.e, check.f, check.g, check.h];
+    return [
+      check.u,
+      check.v,
+      check.w,
+      check.x,
+      check.y,
+      check.z,
+      check.a,
+      check.b,
+      check.c,
+      check.d,
+      check.e,
+      check.f,
+      check.g,
+      check.h
+    ];
   }
 
   /**
@@ -61,7 +74,7 @@ export default class UkModulusChecking {
    */
 
   getNumber(check, number) {
-    let sortCode = this.sortCode;
+    let { sortCode } = this;
 
     number = number || this.accountNumber;
 
@@ -123,7 +136,12 @@ export default class UkModulusChecking {
       return true;
     }
 
-    if (check.exception === 6 && this.pickPosition(number, 'a') >= 4 && this.pickPosition(number, 'a') <= 8 && this.pickPosition(number, 'g') === this.pickPosition(number, 'h')) {
+    if (
+      check.exception === 6 &&
+      this.pickPosition(number, 'a') >= 4 &&
+      this.pickPosition(number, 'a') <= 8 &&
+      this.pickPosition(number, 'g') === this.pickPosition(number, 'h')
+    ) {
       return true;
     }
 
@@ -199,46 +217,46 @@ export default class UkModulusChecking {
    * Is valid.
    */
 
-   isValid() {
-     if (this.accountNumber.length < 6 || this.accountNumber.length > 10 || this.sortCode.length !== 6) {
-       return false;
-     }
+  isValid() {
+    if (this.accountNumber.length < 6 || this.accountNumber.length > 10 || this.sortCode.length !== 6) {
+      return false;
+    }
 
-     const checks = this.getSortCodeChecks();
+    const checks = this.getSortCodeChecks();
 
-     // If no range is found that contains the sorting code, there is no modulus check that can be performed.
-     // The sorting code and account number should be presumed valid unless other evidence implies otherwise.
-     if (checks.length === 0) {
-       return true;
-     }
+    // If no range is found that contains the sorting code, there is no modulus check that can be performed.
+    // The sorting code and account number should be presumed valid unless other evidence implies otherwise.
+    if (checks.length === 0) {
+      return true;
+    }
 
-     const firstCheck = checks[0];
+    const [firstCheck] = checks;
 
-     if (this.isCheckValid(firstCheck)) {
-       if (checks.length === 1 || [2, 9, 10, 11, 12, 13, 14].indexOf(firstCheck.exception) !== -1) {
-         return true;
-       }
+    if (this.isCheckValid(firstCheck)) {
+      if (checks.length === 1 || [2, 9, 10, 11, 12, 13, 14].indexOf(firstCheck.exception) !== -1) {
+        return true;
+      }
 
-       // Verify second check.
-       return this.isCheckValid(checks[1]);
-     }
+      // Verify second check.
+      return this.isCheckValid(checks[1]);
+    }
 
-     if (firstCheck.exception === 14) {
-       if ([0, 1, 9].indexOf(parseInt(this.accountNumber.charAt(7), 10)) === -1) {
-         return false;
-       }
+    if (firstCheck.exception === 14) {
+      if ([0, 1, 9].indexOf(parseInt(this.accountNumber.charAt(7), 10)) === -1) {
+        return false;
+      }
 
-       //  If the 8th digit is 0, 1 or 9, then remove the digit from the account number and insert a 0 as the 1st digit for check purposes only
-       return this.isCheckValid(checks[0], `0${this.accountNumber.substring(7, 0)}`);
-     }
+      //  If the 8th digit is 0, 1 or 9, then remove the digit from the account number and insert a 0 as the 1st digit for check purposes only.
+      return this.isCheckValid(checks[0], `0${this.accountNumber.substring(7, 0)}`);
+    }
 
-     if (checks.length === 1 || [2, 9, 10, 11, 12, 13, 14].indexOf(firstCheck.exception) === -1) {
-       return false;
-     }
+    if (checks.length === 1 || [2, 9, 10, 11, 12, 13, 14].indexOf(firstCheck.exception) === -1) {
+      return false;
+    }
 
-     // Verify second check.
-     return this.isCheckValid(checks[1]);
-   }
+    // Verify second check.
+    return this.isCheckValid(checks[1]);
+  }
 
   /**
    * Load scsubtab file.
@@ -248,7 +266,7 @@ export default class UkModulusChecking {
     const content = fs.readFileSync(path.join(__dirname, 'data', 'scsubtab.txt'), 'utf8');
     const scsubtab = [];
 
-    content.split('\r\n').forEach((line) => {
+    content.split('\r\n').forEach(line => {
       const data = line.split(/\s+/);
 
       scsubtab.push({
@@ -268,10 +286,10 @@ export default class UkModulusChecking {
     const content = fs.readFileSync(path.join(__dirname, 'data', 'valacdos-v900.txt'), 'utf8');
     const valacdos = [];
 
-    content.split('\r\n').forEach((line) => {
+    content.split('\r\n').forEach(line => {
       const data = line.split(/\s+/);
 
-      /* jscs:disable validateOrderInObjectKeys */
+      /* eslint-disable sort-keys-fix/sort-keys-fix */
       valacdos.push({
         start: parseInt(data[0], 10),
         end: parseInt(data[1], 10),
@@ -292,7 +310,7 @@ export default class UkModulusChecking {
         h: parseInt(data[16], 10),
         exception: parseInt(data[17], 10) || null
       });
-      /* jscs:enable validateOrderInObjectKeys */
+      /* eslint-enable sort-keys-fix/sort-keys-fix */
     });
 
     return valacdos;
@@ -302,9 +320,9 @@ export default class UkModulusChecking {
    * Pick position in number.
    */
 
-   pickPosition(number, position) {
-     return parseInt(number.charAt(positions[position]), 10);
-   }
+  pickPosition(number, position) {
+    return parseInt(number.charAt(positions[position]), 10);
+  }
 
   /**
    * Sanitize.
diff --git a/test/index_test.js b/test/index_test.js
index 25cc4f1..ee646c0 100644
--- a/test/index_test.js
+++ b/test/index_test.js
@@ -1,4 +1,3 @@
-
 /**
  * Module dependencies.
  */
@@ -50,29 +49,33 @@ const accounts = {
  * Test `UkModulusChecking`.
  */
 
-describe('UkModulusChecking', () => {
-  describe('isValid()', () => {
-    it('should return false if account number length is less than 6', () => {
+describe('UkModulusChecking', function () {
+  describe('isValid()', function () {
+    it('should return false if account number length is less than 6', function () {
       new UkModulusChecking({ accountNumber: '12345', sortCode: '123456' }).isValid().should.be.false();
     });
 
-    it('should return false if account number length is greater than 10', () => {
+    it('should return false if account number length is greater than 10', function () {
       new UkModulusChecking({ accountNumber: '12345678901', sortCode: '123456' }).isValid().should.be.false();
     });
 
-    it('should return false if sort code length is not 6', () => {
+    it('should return false if sort code length is not 6', function () {
       new UkModulusChecking({ accountNumber: '12345789', sortCode: '12345' }).isValid().should.be.false();
     });
 
-    accounts.invalid.forEach((account) => {
-      it(`should return false if sort code is ${account.sortCode} and account number is ${account.accountNumber}`, () => {
-        new UkModulusChecking({ accountNumber: account.accountNumber, sortCode: account.sortCode }).isValid().should.be.false();
+    accounts.invalid.forEach(account => {
+      it(`should return false if sort code is ${account.sortCode} and account number is ${account.accountNumber}`, function () {
+        new UkModulusChecking({ accountNumber: account.accountNumber, sortCode: account.sortCode })
+          .isValid()
+          .should.be.false();
       });
     });
 
-    accounts.valid.forEach((account) => {
-      it(`should return true if sort code is ${account.sortCode} and account number is ${account.accountNumber}`, () => {
-        new UkModulusChecking({ accountNumber: account.accountNumber, sortCode: account.sortCode }).isValid().should.be.true();
+    accounts.valid.forEach(account => {
+      it(`should return true if sort code is ${account.sortCode} and account number is ${account.accountNumber}`, function () {
+        new UkModulusChecking({ accountNumber: account.accountNumber, sortCode: account.sortCode })
+          .isValid()
+          .should.be.true();
       });
     });
   });