diff --git a/.github/workflows/pr-labeler.yml b/.github/workflows/pr-labeler.yml
index f0fe72f6..98d0d354 100644
--- a/.github/workflows/pr-labeler.yml
+++ b/.github/workflows/pr-labeler.yml
@@ -1,6 +1,6 @@
 name: "PR: Labeler"
 on:
-  pull_request:
+  pull_request_target:
 
 permissions:
   contents: read
diff --git a/lib/cli/src/__tests__/commands/check/utils/check-matching-routes.test.ts b/lib/cli/src/__tests__/commands/check/utils/check-matching-routes.test.ts
index a65831ac..3fbd6de2 100644
--- a/lib/cli/src/__tests__/commands/check/utils/check-matching-routes.test.ts
+++ b/lib/cli/src/__tests__/commands/check/utils/check-matching-routes.test.ts
@@ -766,4 +766,302 @@ describe("checkMatchingRoutes", () => {
       })
     );
   });
+
+  // ############################################################
+  // Status code validation - extra status codes are allowed
+  // ############################################################
+
+  it("should ignore extra status codes in implementation", () => {
+    // Arrange - Base has 200 and 400, impl adds 401 and 403
+    const baseDoc: OpenAPIV3.Document = {
+      openapi: "3.0.0",
+      info: { title: "Base", version: "1.0.0" },
+      paths: {
+        "/foo": {
+          get: {
+            responses: {
+              "200": { description: "OK" },
+              "400": { description: "Bad Request" },
+            },
+          },
+        },
+      },
+    };
+
+    const implDoc: OpenAPIV3.Document = {
+      openapi: "3.0.0",
+      info: { title: "Impl", version: "1.0.0" },
+      paths: {
+        "/foo": {
+          get: {
+            responses: {
+              "200": { description: "OK" },
+              "400": { description: "Bad Request" },
+              "401": { description: "Unauthorized" },
+              "403": { description: "Forbidden" },
+            },
+          },
+        },
+      },
+    };
+
+    // Act
+    const errors = checkMatchingRoutes(baseDoc, implDoc);
+
+    // Assert - No errors because extra status codes are allowed
+    expect(errors.getErrorCount()).toBe(0);
+  });
+
+  // ############################################################
+  // MIME type validation - extra mime types are allowed
+  // ############################################################
+
+  it("should ignore extra mime types in implementation response", () => {
+    // Arrange - Base has application/json, impl adds application/xml
+    const baseDoc: OpenAPIV3.Document = {
+      openapi: "3.0.0",
+      info: { title: "Base", version: "1.0.0" },
+      paths: {
+        "/foo": {
+          get: {
+            responses: {
+              "200": {
+                description: "OK",
+                content: {
+                  "application/json": {
+                    schema: { type: "object" },
+                  },
+                },
+              },
+            },
+          },
+        },
+      },
+    };
+
+    const implDoc: OpenAPIV3.Document = {
+      openapi: "3.0.0",
+      info: { title: "Impl", version: "1.0.0" },
+      paths: {
+        "/foo": {
+          get: {
+            responses: {
+              "200": {
+                description: "OK",
+                content: {
+                  "application/json": {
+                    schema: { type: "object" },
+                  },
+                  "application/xml": {
+                    schema: { type: "object" },
+                  },
+                },
+              },
+            },
+          },
+        },
+      },
+    };
+
+    // Act
+    const errors = checkMatchingRoutes(baseDoc, implDoc);
+
+    // Assert - No errors because extra mime types are allowed
+    expect(errors.getErrorCount()).toBe(0);
+  });
+
+  // ############################################################
+  // MIME type validation - missing mime type is an error
+  // ############################################################
+
+  it("should detect missing mime type in implementation response", () => {
+    // Arrange - Base has json and xml, impl only has json
+    const baseDoc: OpenAPIV3.Document = {
+      openapi: "3.0.0",
+      info: { title: "Base", version: "1.0.0" },
+      paths: {
+        "/foo": {
+          get: {
+            responses: {
+              "200": {
+                description: "OK",
+                content: {
+                  "application/json": {
+                    schema: { type: "object" },
+                  },
+                  "application/xml": {
+                    schema: { type: "object" },
+                  },
+                },
+              },
+            },
+          },
+        },
+      },
+    };
+
+    const implDoc: OpenAPIV3.Document = {
+      openapi: "3.0.0",
+      info: { title: "Impl", version: "1.0.0" },
+      paths: {
+        "/foo": {
+          get: {
+            responses: {
+              "200": {
+                description: "OK",
+                content: {
+                  "application/json": {
+                    schema: { type: "object" },
+                  },
+                },
+              },
+            },
+          },
+        },
+      },
+    };
+
+    // Act
+    const errors = checkMatchingRoutes(baseDoc, implDoc);
+
+    // Assert
+    expect(errors.getErrorCount()).toBe(1);
+    expect(errors.get(0)).toEqual(
+      expect.objectContaining({
+        type: "ROUTE_CONFLICT",
+        subType: "RESPONSE_BODY_CONFLICT",
+        endpoint: "GET /foo",
+        message: expect.stringMatching(
+          /Implementation missing schema for expected mime type \[application\/xml\]/
+        ),
+      })
+    );
+  });
+
+  // ############################################################
+  // Query parameter validation - extra params not flagged
+  // ############################################################
+
+  // TODO: README Query param case 1 says extra query params should produce a
+  // warning. Current impl only iterates over base params, so extras are silently
+  // ignored. Update test to assert a warning when impl is fixed.
+  it("should not flag extra query parameters in implementation (known deviation from README spec)", () => {
+    // Arrange - Impl has an extra parameter not in base
+    const baseDoc: OpenAPIV3.Document = {
+      openapi: "3.0.0",
+      info: { title: "Base", version: "1.0.0" },
+      paths: {
+        "/search": {
+          get: {
+            parameters: [
+              {
+                name: "required_param",
+                in: "query",
+                required: true,
+                schema: { type: "string" },
+              },
+            ],
+            responses: {
+              "200": { description: "OK" },
+            },
+          },
+        },
+      },
+    };
+
+    const implDoc: OpenAPIV3.Document = {
+      openapi: "3.0.0",
+      info: { title: "Impl", version: "1.0.0" },
+      paths: {
+        "/search": {
+          get: {
+            parameters: [
+              {
+                name: "required_param",
+                in: "query",
+                required: true,
+                schema: { type: "string" },
+              },
+              {
+                name: "extra_param",
+                in: "query",
+                required: false,
+                schema: { type: "string" },
+              },
+            ],
+            responses: {
+              "200": { description: "OK" },
+            },
+          },
+        },
+      },
+    };
+
+    // Act
+    const errors = checkMatchingRoutes(baseDoc, implDoc);
+
+    // Assert
+    expect(errors.getErrorCount()).toBe(0);
+  });
+
+  // ############################################################
+  // Query parameter validation - missing optional param
+  // ############################################################
+
+  // TODO: README Query param case 2.2 says missing optional params should warn,
+  // not error. Current impl flags all missing params as "Missing required query
+  // parameter" regardless of required status. Update test when impl is fixed.
+  it("should flag missing optional query parameter as error (known deviation from README spec)", () => {
+    // Arrange - Base has an optional param, impl doesn't have it
+    const baseDoc: OpenAPIV3.Document = {
+      openapi: "3.0.0",
+      info: { title: "Base", version: "1.0.0" },
+      paths: {
+        "/search": {
+          get: {
+            parameters: [
+              {
+                name: "optional_param",
+                in: "query",
+                required: false,
+                schema: { type: "string" },
+              },
+            ],
+            responses: {
+              "200": { description: "OK" },
+            },
+          },
+        },
+      },
+    };
+
+    const implDoc: OpenAPIV3.Document = {
+      openapi: "3.0.0",
+      info: { title: "Impl", version: "1.0.0" },
+      paths: {
+        "/search": {
+          get: {
+            parameters: [],
+            responses: {
+              "200": { description: "OK" },
+            },
+          },
+        },
+      },
+    };
+
+    // Act
+    const errors = checkMatchingRoutes(baseDoc, implDoc);
+
+    // Assert
+    expect(errors.getErrorCount()).toBe(1);
+    expect(errors.get(0)).toEqual(
+      expect.objectContaining({
+        type: "ROUTE_CONFLICT",
+        subType: "QUERY_PARAM_CONFLICT",
+        endpoint: "GET /search",
+        message: expect.stringMatching(/Missing required query parameter \[optional_param\]/),
+      })
+    );
+  });
 });
diff --git a/lib/cli/src/__tests__/commands/check/utils/check-schema-compatibility.test.ts b/lib/cli/src/__tests__/commands/check/utils/check-schema-compatibility.test.ts
index 1c711e9d..1c2130f2 100644
--- a/lib/cli/src/__tests__/commands/check/utils/check-schema-compatibility.test.ts
+++ b/lib/cli/src/__tests__/commands/check/utils/check-schema-compatibility.test.ts
@@ -544,4 +544,153 @@ describe("Schema Compatibility Checks", () => {
       })
     );
   });
+
+  // ############################################################
+  // Type checking - simple type matches (README: Type case 3)
+  // ############################################################
+
+  it("should pass when simple types match exactly", () => {
+    // Arrange - Both base and impl have the same string type
+    // README: Type case 3 - Simple type matches -> Ignore
+    const baseSchema: OpenAPIV3.SchemaObject = {
+      type: "object",
+      properties: {
+        name: { type: "string" },
+      },
+    };
+
+    const implSchema: OpenAPIV3.SchemaObject = {
+      type: "object",
+      properties: {
+        name: { type: "string" },
+      },
+    };
+
+    // Act
+    const errors = checkSchemaCompatibility(location, baseSchema, implSchema, ctx);
+
+    // Assert - No errors because types match
+    expect(errors.getErrorCount()).toBe(0);
+  });
+
+  // ############################################################
+  // Enum validation - enums match (README: Enum case 1)
+  // ############################################################
+
+  it("should pass when enum values match exactly", () => {
+    // Arrange - Both base and impl have the same enum values
+    // README: Enum case 1 - Enums match -> Ignore
+    const baseSchema: OpenAPIV3.SchemaObject = {
+      type: "string",
+      enum: ["active", "inactive"],
+    };
+
+    const implSchema: OpenAPIV3.SchemaObject = {
+      type: "string",
+      enum: ["active", "inactive"],
+    };
+
+    // Act
+    const errors = checkSchemaCompatibility(location, baseSchema, implSchema, ctx);
+
+    // Assert - No errors because enums match
+    expect(errors.getErrorCount()).toBe(0);
+  });
+
+  // ############################################################
+  // Enum validation - base has extra values (README: Enum case 2)
+  // ############################################################
+
+  it("should pass when base has more enum values than impl", () => {
+    // Arrange - Base has extra enum value "pending" not in impl
+    // README: Enum case 2 - Base type has extra -> Ignore
+    // Impl can support a subset because a valid impl input is still valid for base
+    const baseSchema: OpenAPIV3.SchemaObject = {
+      type: "string",
+      enum: ["active", "inactive", "pending"],
+    };
+
+    const implSchema: OpenAPIV3.SchemaObject = {
+      type: "string",
+      enum: ["active", "inactive"],
+    };
+
+    // Act
+    const errors = checkSchemaCompatibility(location, baseSchema, implSchema, ctx);
+
+    // Assert - No errors because impl is a subset of base
+    expect(errors.getErrorCount()).toBe(0);
+  });
+
+  // ############################################################
+  // Missing optional property emits warning (README: Schema case 2.2)
+  // ############################################################
+
+  it("should not error when missing property is optional in base schema", () => {
+    // Arrange - "description" is optional (not in required array)
+    // README: Schema case 2.2 - Missing optional prop -> Warn
+    // NOTE: Current implementation silently ignores missing optional props
+    // rather than emitting a warning. This test documents the current behavior.
+    const baseSchema: OpenAPIV3.SchemaObject = {
+      type: "object",
+      properties: {
+        name: { type: "string" },
+        description: { type: "string" },
+      },
+      // 'description' is NOT in required, so it's optional
+    };
+
+    const implSchema: OpenAPIV3.SchemaObject = {
+      type: "object",
+      properties: {
+        name: { type: "string" },
+        // missing optional 'description' property
+      },
+    };
+
+    // Act
+    const errors = checkSchemaCompatibility(location, baseSchema, implSchema, ctx);
+
+    // Assert - No errors because 'description' is optional
+    expect(errors.getErrorCount()).toBe(0);
+  });
+
+  // ############################################################
+  // Additional properties - default (undefined) allows extras
+  // (README: Schema case 1.1 variant - additionalProperties not set)
+  // ############################################################
+
+  // TODO: README Schema case 1.1 says undefined additionalProperties should
+  // allow extras. Current impl treats undefined as disallowed and flags an
+  // error. See TODO in check-schema-compatibility.ts:198. Update test when fixed.
+  it("should flag extra properties when additionalProperties is not set (known deviation from README spec)", () => {
+    // Arrange - additionalProperties is undefined
+    // README says this should allow extras, but current impl flags them
+    const baseSchema: OpenAPIV3.SchemaObject = {
+      type: "object",
+      properties: {
+        name: { type: "string" },
+      },
+    };
+
+    const implSchema: OpenAPIV3.SchemaObject = {
+      type: "object",
+      properties: {
+        name: { type: "string" },
+        extra_prop: { type: "string" },
+      },
+    };
+
+    // Act
+    const errors = checkSchemaCompatibility(location, baseSchema, implSchema, ctx);
+
+    // Assert
+    expect(errors.getErrorCount()).toBe(1);
+    expect(errors.get(0)).toEqual(
+      expect.objectContaining({
+        conflictType: "EXTRA_FIELD",
+        location: `${location}.extra_prop`,
+      })
+    );
+  });
 });