diff --git a/packages/core/src/ruleset/meta/json-extensions.json b/packages/core/src/ruleset/meta/json-extensions.json
index b57698d83..f3c6186ec 100644
--- a/packages/core/src/ruleset/meta/json-extensions.json
+++ b/packages/core/src/ruleset/meta/json-extensions.json
@@ -36,22 +36,7 @@
     },
     "Format": {
       "$anchor": "format",
-      "enum": [
-        "oas2",
-        "oas3",
-        "oas3.0",
-        "oas3.1",
-        "asyncapi2",
-        "json-schema",
-        "json-schema-loose",
-        "json-schema-draft4",
-        "json-schema-draft6",
-        "json-schema-draft7",
-        "json-schema-draft-2019-09",
-        "json-schema-2019-09",
-        "json-schema-draft-2020-12",
-        "json-schema-2020-12"
-      ],
+      "type": "string",
       "errorMessage": "must be a valid format"
     },
     "Functions": {
diff --git a/packages/core/src/ruleset/validation/__tests__/validation.test.ts b/packages/core/src/ruleset/validation/__tests__/validation.test.ts
index 001427667..3cfab69b9 100644
--- a/packages/core/src/ruleset/validation/__tests__/validation.test.ts
+++ b/packages/core/src/ruleset/validation/__tests__/validation.test.ts
@@ -941,14 +941,14 @@ describe('JSON Ruleset Validation', () => {
 
   it.each<[unknown, RulesetValidationError[]]>([
     [
-      [2, 'a'],
+      [2, null],
       [
         new RulesetValidationError('invalid-format', 'must be a valid format', ['formats', '0']),
         new RulesetValidationError('invalid-format', 'must be a valid format', ['formats', '1']),
       ],
     ],
     [2, [new RulesetValidationError('invalid-ruleset-definition', 'must be an array of formats', ['formats'])]],
-    [[''], [new RulesetValidationError('invalid-format', 'must be a valid format', ['formats', '0'])]],
+    [[null], [new RulesetValidationError('invalid-format', 'must be a valid format', ['formats', '0'])]],
   ])('recognizes invalid ruleset %p formats syntax', (formats, errors) => {
     expect(
       assertValidRuleset.bind(
@@ -985,7 +985,7 @@ describe('JSON Ruleset Validation', () => {
 
   it.each<[unknown, RulesetValidationError[]]>([
     [
-      [2, 'a'],
+      [2, null],
       [
         new RulesetValidationError('invalid-format', 'must be a valid format', ['rules', 'rule', 'formats', '0']),
         new RulesetValidationError('invalid-format', 'must be a valid format', ['rules', 'rule', 'formats', '1']),