diff --git a/.github/workflows/format.yml b/.github/workflows/format.yml
new file mode 100644
index 0000000..cb67a35
--- /dev/null
+++ b/.github/workflows/format.yml
@@ -0,0 +1,32 @@
+name: Format
+
+on:
+    push:
+        branches: [main]
+    pull_request:
+        branches: [main]
+    workflow_dispatch:
+
+permissions:
+    contents: read
+
+jobs:
+    prettier:
+        name: Prettier
+        runs-on: ubuntu-latest
+
+        steps:
+            - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+
+            - name: Setup Node.js
+              uses: ./.github/actions/setup-node-cached
+              with:
+                  node-version: '24'
+
+            - name: Install dependencies
+              run: npm install
+
+            # No paths filter: most of what drifted out of style lives at the
+            # repo root, which the js-ci and php-ci filters never match.
+            - name: Check formatting
+              run: npx prettier --check . --ignore-path .gitignore --ignore-path .prettierignore
diff --git a/.prettierignore b/.prettierignore
new file mode 100644
index 0000000..b7e2c14
--- /dev/null
+++ b/.prettierignore
@@ -0,0 +1,13 @@
+# Generated by release-please — reformatting them only creates churn, since
+# the next release rewrites them in its own style.
+CHANGELOG.md
+packages/*/CHANGELOG.md
+.release-please-manifest.json
+
+# Test fixtures are inputs, not source. Their exact bytes are what is under
+# test — indentation included.
+packages/php/tests/Fixtures/
+
+# Infection reads json5; Prettier rewrites the quoting style, which would
+# fork this file away from its twin in safeaccess-identum.
+packages/php/infection.json5
diff --git a/codecov.yml b/codecov.yml
index c4f3dd1..1bef090 100644
--- a/codecov.yml
+++ b/codecov.yml
@@ -16,6 +16,6 @@ flags:
         carryforward: false
 
 comment:
-    layout: "condensed_header, flags, tree"
+    layout: 'condensed_header, flags, tree'
     behavior: default
     require_changes: false
diff --git a/commitlint.config.js b/commitlint.config.js
index df4852c..7a9257d 100644
--- a/commitlint.config.js
+++ b/commitlint.config.js
@@ -1,11 +1,7 @@
 export default {
-  extends: ['@commitlint/config-conventional'],
-  rules: {
-    'scope-enum': [
-      2,
-      'always',
-      ['js', 'php', 'docs', 'ci', 'deps'],
-    ],
-    'scope-empty': [1, 'never'],
-  },
+    extends: ['@commitlint/config-conventional'],
+    rules: {
+        'scope-enum': [2, 'always', ['js', 'php', 'docs', 'ci', 'deps']],
+        'scope-empty': [1, 'never'],
+    },
 };
diff --git a/eslint.config.js b/eslint.config.js
index 4513671..d7604c9 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -1,5 +1,5 @@
-import eslint from "@eslint/js";
-import tseslint from "typescript-eslint";
+import eslint from '@eslint/js';
+import tseslint from 'typescript-eslint';
 
 /**
  * Shared ESLint configuration for all TypeScript packages in the monorepo.
@@ -10,14 +10,11 @@ export default tseslint.config(
     ...tseslint.configs.recommended,
     {
         rules: {
-            "@typescript-eslint/no-explicit-any": "error",
-            "@typescript-eslint/no-unused-vars": [
-                "error",
-                { argsIgnorePattern: "^_" },
-            ],
+            '@typescript-eslint/no-explicit-any': 'error',
+            '@typescript-eslint/no-unused-vars': ['error', { argsIgnorePattern: '^_' }],
         },
     },
     {
-        ignores: ["dist/", "node_modules/"],
+        ignores: ['dist/', 'node_modules/'],
     },
 );
diff --git a/packages/js/src/core/inline-builder-accessor.ts b/packages/js/src/core/inline-builder-accessor.ts
index 4f2633f..feb4218 100644
--- a/packages/js/src/core/inline-builder-accessor.ts
+++ b/packages/js/src/core/inline-builder-accessor.ts
@@ -84,13 +84,15 @@ export class InlineBuilderAccessor {
      * @returns New builder instance with the integration configured.
      */
     withParserIntegration(integration: ParseIntegrationInterface): this {
-        return new (this.constructor as new (
-            guard: SecurityGuardInterface,
-            secParser: SecurityParserInterface,
-            pathCache: PathCacheInterface | null,
-            integration: ParseIntegrationInterface | null,
-            strictMode: boolean | null,
-        ) => this)(this._guard, this._secParser, this._pathCache, integration, this._strictMode);
+        return new (
+            this.constructor as new (
+                guard: SecurityGuardInterface,
+                secParser: SecurityParserInterface,
+                pathCache: PathCacheInterface | null,
+                integration: ParseIntegrationInterface | null,
+                strictMode: boolean | null,
+            ) => this
+        )(this._guard, this._secParser, this._pathCache, integration, this._strictMode);
     }
 
     /**
@@ -100,13 +102,15 @@ export class InlineBuilderAccessor {
      * @returns New builder instance with the guard configured.
      */
     withSecurityGuard(guard: SecurityGuardInterface): this {
-        return new (this.constructor as new (
-            guard: SecurityGuardInterface,
-            secParser: SecurityParserInterface,
-            pathCache: PathCacheInterface | null,
-            integration: ParseIntegrationInterface | null,
-            strictMode: boolean | null,
-        ) => this)(guard, this._secParser, this._pathCache, this._integration, this._strictMode);
+        return new (
+            this.constructor as new (
+                guard: SecurityGuardInterface,
+                secParser: SecurityParserInterface,
+                pathCache: PathCacheInterface | null,
+                integration: ParseIntegrationInterface | null,
+                strictMode: boolean | null,
+            ) => this
+        )(guard, this._secParser, this._pathCache, this._integration, this._strictMode);
     }
 
     /**
@@ -116,13 +120,15 @@ export class InlineBuilderAccessor {
      * @returns New builder instance with the parser configured.
      */
     withSecurityParser(parser: SecurityParserInterface): this {
-        return new (this.constructor as new (
-            guard: SecurityGuardInterface,
-            secParser: SecurityParserInterface,
-            pathCache: PathCacheInterface | null,
-            integration: ParseIntegrationInterface | null,
-            strictMode: boolean | null,
-        ) => this)(this._guard, parser, this._pathCache, this._integration, this._strictMode);
+        return new (
+            this.constructor as new (
+                guard: SecurityGuardInterface,
+                secParser: SecurityParserInterface,
+                pathCache: PathCacheInterface | null,
+                integration: ParseIntegrationInterface | null,
+                strictMode: boolean | null,
+            ) => this
+        )(this._guard, parser, this._pathCache, this._integration, this._strictMode);
     }
 
     /**
@@ -132,13 +138,15 @@ export class InlineBuilderAccessor {
      * @returns New builder instance with the cache configured.
      */
     withPathCache(cache: PathCacheInterface): this {
-        return new (this.constructor as new (
-            guard: SecurityGuardInterface,
-            secParser: SecurityParserInterface,
-            pathCache: PathCacheInterface | null,
-            integration: ParseIntegrationInterface | null,
-            strictMode: boolean | null,
-        ) => this)(this._guard, this._secParser, cache, this._integration, this._strictMode);
+        return new (
+            this.constructor as new (
+                guard: SecurityGuardInterface,
+                secParser: SecurityParserInterface,
+                pathCache: PathCacheInterface | null,
+                integration: ParseIntegrationInterface | null,
+                strictMode: boolean | null,
+            ) => this
+        )(this._guard, this._secParser, cache, this._integration, this._strictMode);
     }
 
     /**
@@ -152,12 +160,14 @@ export class InlineBuilderAccessor {
      *           Only use with fully trusted, application-controlled input.
      */
     withStrictMode(strict: boolean): this {
-        return new (this.constructor as new (
-            guard: SecurityGuardInterface,
-            secParser: SecurityParserInterface,
-            pathCache: PathCacheInterface | null,
-            integration: ParseIntegrationInterface | null,
-            strictMode: boolean | null,
-        ) => this)(this._guard, this._secParser, this._pathCache, this._integration, strict);
+        return new (
+            this.constructor as new (
+                guard: SecurityGuardInterface,
+                secParser: SecurityParserInterface,
+                pathCache: PathCacheInterface | null,
+                integration: ParseIntegrationInterface | null,
+                strictMode: boolean | null,
+            ) => this
+        )(this._guard, this._secParser, this._pathCache, this._integration, strict);
     }
 }
diff --git a/packages/js/tsconfig.json b/packages/js/tsconfig.json
index 6c931f5..8af2ab8 100644
--- a/packages/js/tsconfig.json
+++ b/packages/js/tsconfig.json
@@ -1,16 +1,16 @@
 {
-  "compilerOptions": {
-    "target": "ES2022",
-    "module": "ESNext",
-    "moduleResolution": "bundler",
-    "strict": true,
-    "declaration": true,
-    "outDir": "./dist",
-    "rootDir": "./src",
-    "noImplicitAny": true,
-    "noImplicitReturns": true,
-    "exactOptionalPropertyTypes": true
-  },
-  "include": ["src/**/*"],
-  "exclude": ["node_modules", "dist", "tests", "vitest.config.ts"]
+    "compilerOptions": {
+        "target": "ES2022",
+        "module": "ESNext",
+        "moduleResolution": "bundler",
+        "strict": true,
+        "declaration": true,
+        "outDir": "./dist",
+        "rootDir": "./src",
+        "noImplicitAny": true,
+        "noImplicitReturns": true,
+        "exactOptionalPropertyTypes": true
+    },
+    "include": ["src/**/*"],
+    "exclude": ["node_modules", "dist", "tests", "vitest.config.ts"]
 }