diff --git a/package.json b/package.json
index 7870ba402..52fe496ae 100644
--- a/package.json
+++ b/package.json
@@ -42,7 +42,7 @@
     "knip": "^5.62.0",
     "lint-staged": "^16.0.0",
     "mocha": "^11.5.0",
-    "prettier": "^3.4.1",
+    "prettier": "^3.7.0",
     "rollup": "^4.52.3",
     "typescript": "^5.8.3",
     "typescript-eslint": "^8.0.0",
diff --git a/packages/core/src/types.ts b/packages/core/src/types.ts
index 95604e70d..1fd839cf7 100644
--- a/packages/core/src/types.ts
+++ b/packages/core/src/types.ts
@@ -447,11 +447,16 @@ export type RuleFixer = (
 	fixer: RuleTextEditor,
 ) => RuleTextEdit | Iterable<RuleTextEdit> | null;
 
+export type MessagePlaceholderData = Record<
+	string,
+	string | number | boolean | bigint | null | undefined
+>;
+
 export interface ViolationReportBase {
 	/**
 	 * The data to insert into the message.
 	 */
-	data?: Record<string, unknown> | undefined;
+	data?: MessagePlaceholderData | undefined;
 
 	/**
 	 * The fix to be applied for the violation.
@@ -485,7 +490,7 @@ export interface SuggestedEditBase {
 	/**
 	 * The data to insert into the message.
 	 */
-	data?: Record<string, unknown> | undefined;
+	data?: MessagePlaceholderData | undefined;
 
 	/**
 	 * The fix to be applied for the suggestion.
@@ -1030,8 +1035,9 @@ export interface BaseConfig<
 /**
  * The overwrites that apply more differing configuration to specific files or directories.
  */
-export interface ConfigOverride<Rules extends RulesConfig = RulesConfig>
-	extends BaseConfig<Rules> {
+export interface ConfigOverride<
+	Rules extends RulesConfig = RulesConfig,
+> extends BaseConfig<Rules> {
 	/**
 	 * The glob patterns for excluded files.
 	 */
diff --git a/packages/core/tests/types/types.test.ts b/packages/core/tests/types/types.test.ts
index 14935c2fe..2861115c1 100644
--- a/packages/core/tests/types/types.test.ts
+++ b/packages/core/tests/types/types.test.ts
@@ -96,15 +96,12 @@ interface TestLanguageOptions extends LanguageOptions {
 	howMuch?: "yes" | "no" | boolean;
 }
 
-class TestSourceCode
-	implements
-		TextSourceCode<{
-			LangOptions: TestLanguageOptions;
-			RootNode: TestRootNode;
-			SyntaxElementWithLoc: unknown;
-			ConfigNode: unknown;
-		}>
-{
+class TestSourceCode implements TextSourceCode<{
+	LangOptions: TestLanguageOptions;
+	RootNode: TestRootNode;
+	SyntaxElementWithLoc: unknown;
+	ConfigNode: unknown;
+}> {
 	text: string;
 	ast: TestRootNode;
 	notMuch: "no" | false;
@@ -323,6 +320,28 @@ const testRule: RuleDefinition<{
 								foo: "foo",
 								bar: 1,
 								baz: true,
+								qux: false,
+								a: 1n,
+								b: null,
+								c: undefined,
+								d: void 0,
+								// @ts-expect-error -- Symbols are not allowed in `data`.
+								e: Symbol("b"),
+								// @ts-expect-error -- Objects are not allowed in `data`.
+								f: {
+									hi: "hi",
+								},
+								// @ts-expect-error -- Arrays are not allowed in `data`.
+								g: [1, 2, 3],
+								// @ts-expect-error -- Sets are not allowed in `data`.
+								h: new Set([1, 2, 3]),
+								// @ts-expect-error -- Maps are not allowed in `data`.
+								i: new Map([
+									["a", 1],
+									["b", 2],
+								]),
+								// @ts-expect-error -- Functions are not allowed in `data`.
+								j: () => {},
 							},
 							// @ts-expect-error -- 'fix' is required in suggestion objects
 							fix: null,
@@ -339,6 +358,28 @@ const testRule: RuleDefinition<{
 						foo: "foo",
 						bar: 1,
 						baz: true,
+						qux: false,
+						a: 1n,
+						b: null,
+						c: undefined,
+						d: void 0,
+						// @ts-expect-error -- Symbols are not allowed in `data`.
+						e: Symbol("b"),
+						// @ts-expect-error -- Objects are not allowed in `data`.
+						f: {
+							hi: "hi",
+						},
+						// @ts-expect-error -- Arrays are not allowed in `data`.
+						g: [1, 2, 3],
+						// @ts-expect-error -- Sets are not allowed in `data`.
+						h: new Set([1, 2, 3]),
+						// @ts-expect-error -- Maps are not allowed in `data`.
+						i: new Map([
+							["a", 1],
+							["b", 2],
+						]),
+						// @ts-expect-error -- Functions are not allowed in `data`.
+						j: () => {},
 					},
 					fix: null,
 					suggest: null,
@@ -394,8 +435,8 @@ const testRuleWithInvalidDefaultOptions: RuleDefinition<{
 testRuleWithInvalidDefaultOptions.meta satisfies RulesMeta | undefined;
 
 type TestRuleDefinition<
-	Options extends
-		Partial<CustomRuleTypeDefinitions> = CustomRuleTypeDefinitions,
+	Options extends Partial<CustomRuleTypeDefinitions> =
+		CustomRuleTypeDefinitions,
 > = CustomRuleDefinitionType<
 	{
 		LangOptions: TestLanguageOptions;
diff --git a/packages/mcp/package.json b/packages/mcp/package.json
index 7227000f6..4a7f90736 100644
--- a/packages/mcp/package.json
+++ b/packages/mcp/package.json
@@ -36,7 +36,7 @@
     "node": "^20.19.0 || ^22.13.0 || >=24"
   },
   "dependencies": {
-    "@modelcontextprotocol/sdk": "^1.22.0",
+    "@modelcontextprotocol/sdk": "1.22.0",
     "eslint": "^9.39.1",
     "zod": "^3.24.4"
   },