diff --git a/packages/core/src/types.ts b/packages/core/src/types.ts
index 971df45ba..a70bbc2b6 100644
--- a/packages/core/src/types.ts
+++ b/packages/core/src/types.ts
@@ -447,11 +447,19 @@ export type RuleFixer = (
 	fixer: RuleTextEditor,
 ) => RuleTextEdit | Iterable<RuleTextEdit> | null;
 
+/**
+ * Data that can be used to fill placeholders in error messages.
+ */
+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 +493,7 @@ 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.
diff --git a/packages/core/tests/types/types.test.ts b/packages/core/tests/types/types.test.ts
index 3719a2f64..2861115c1 100644
--- a/packages/core/tests/types/types.test.ts
+++ b/packages/core/tests/types/types.test.ts
@@ -320,6 +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,
@@ -336,6 +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,