diff --git a/eslint.config.js b/eslint.config.js
index 66aa6a6fc..60798d6f9 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -216,6 +216,7 @@ export default tsPlugin.config(
     name: "source/ez",
     files: ["express-zod-api/src/*.ts"],
     rules: {
+      complexity: ["error", 20],
       "allowed/dependencies": ["error", { packageDir: ezDir }],
       "no-restricted-syntax": [
         "warn",
diff --git a/express-zod-api/src/json-schema-helpers.ts b/express-zod-api/src/json-schema-helpers.ts
index 1d96da0da..04d94a164 100644
--- a/express-zod-api/src/json-schema-helpers.ts
+++ b/express-zod-api/src/json-schema-helpers.ts
@@ -2,17 +2,24 @@ import * as R from "ramda";
 import { combinations, FlatObject, isObject } from "./common-helpers";
 import type { z } from "zod";
 
-const isJsonObjectSchema = (
+type MergeMode = "coerce" | "throw";
+type FlattenObjectSchema = z.core.JSONSchema.ObjectSchema &
+  Required<Pick<z.core.JSONSchema.ObjectSchema, "properties">>;
+
+/** @internal */
+export const isJsonObjectSchema = (
   subject: z.core.JSONSchema.BaseSchema,
 ): subject is z.core.JSONSchema.ObjectSchema => subject.type === "object";
 
-const propsMerger = R.mergeDeepWith((a: unknown, b: unknown) => {
+/** @internal */
+export const propsMerger = R.mergeDeepWith((a: unknown, b: unknown) => {
   if (Array.isArray(a) && Array.isArray(b)) return R.concat(a, b);
   if (a === b) return b;
   throw new Error("Can not flatten properties", { cause: { a, b } });
 });
 
-const canMerge = R.pipe(
+/** @internal */
+export const canMerge = R.pipe(
   Object.keys,
   R.without([
     "type",
@@ -25,33 +32,65 @@ const canMerge = R.pipe(
   R.isEmpty,
 );
 
-const nestOptional = R.pair(true);
+/** @internal */
+export const nestOptional = R.pair(true)<z.core.JSONSchema.BaseSchema>;
+type Stack = Array<ReturnType<typeof nestOptional>>;
+
+/** @internal */
+export const processAllOf = (
+  subject: z.core.JSONSchema.BaseSchema,
+  mode: MergeMode,
+  isOptional: boolean,
+) => {
+  if (!("allOf" in subject) || !subject.allOf) return [];
+  return subject.allOf.map((one) => {
+    if (mode === "throw" && !(one.type === "object" && canMerge(one)))
+      throw new Error("Can not merge");
+    return R.pair(isOptional, one);
+  });
+};
+
+/** @internal */
+export const processVariants = (subject: z.core.JSONSchema.BaseSchema) => {
+  const result: Stack = [];
+  if (subject.anyOf) result.push(...R.map(nestOptional, subject.anyOf));
+  if (subject.oneOf) result.push(...R.map(nestOptional, subject.oneOf));
+  return result;
+};
+
+/** @internal */
+export const processPropertyNames = (
+  subject: z.core.JSONSchema.ObjectSchema,
+  target: FlattenObjectSchema,
+  requiredKeys: string[],
+  isOptional: boolean,
+) => {
+  if (!isObject(subject.propertyNames)) return;
+  const keys: string[] = [];
+  if (typeof subject.propertyNames.const === "string")
+    keys.push(subject.propertyNames.const);
+  if (subject.propertyNames.enum) {
+    keys.push(
+      ...subject.propertyNames.enum.filter((one) => typeof one === "string"),
+    );
+  }
+  const value = { ...Object(subject.additionalProperties) }; // it can be bool
+  for (const key of keys) target.properties[key] ??= value;
+  if (!isOptional) requiredKeys.push(...keys);
+};
 
 export const flattenIO = (
   jsonSchema: z.core.JSONSchema.BaseSchema,
-  mode: "coerce" | "throw" = "coerce",
+  mode: MergeMode = "coerce",
 ) => {
-  const stack = [R.pair(false, jsonSchema)]; // [isOptional, JSON Schema]
-  const flat: z.core.JSONSchema.ObjectSchema &
-    Required<Pick<z.core.JSONSchema.ObjectSchema, "properties">> = {
-    type: "object",
-    properties: {},
-  };
+  const stack: Stack = [R.pair(false, jsonSchema)]; // [isOptional, JSON Schema]
+  const flat: FlattenObjectSchema = { type: "object", properties: {} };
   const flatRequired: string[] = [];
   while (stack.length) {
     const [isOptional, entry] = stack.shift()!;
     if (entry.description) flat.description ??= entry.description;
-    if (entry.allOf) {
-      stack.push(
-        ...entry.allOf.map((one) => {
-          if (mode === "throw" && !(one.type === "object" && canMerge(one)))
-            throw new Error("Can not merge");
-          return R.pair(isOptional, one);
-        }),
-      );
-    }
-    if (entry.anyOf) stack.push(...R.map(nestOptional, entry.anyOf));
-    if (entry.oneOf) stack.push(...R.map(nestOptional, entry.oneOf));
+    stack.push(...processAllOf(entry, mode, isOptional));
+    stack.push(...processVariants(entry));
     if (entry.examples?.length) {
       if (isOptional) {
         flat.examples = R.concat(flat.examples || [], entry.examples);
@@ -72,19 +111,7 @@ export const flattenIO = (
       );
       if (!isOptional && entry.required) flatRequired.push(...entry.required);
     }
-    if (isObject(entry.propertyNames)) {
-      const keys: string[] = [];
-      if (typeof entry.propertyNames.const === "string")
-        keys.push(entry.propertyNames.const);
-      if (entry.propertyNames.enum) {
-        keys.push(
-          ...entry.propertyNames.enum.filter((one) => typeof one === "string"),
-        );
-      }
-      const value = { ...Object(entry.additionalProperties) }; // it can be bool
-      for (const key of keys) flat.properties[key] ??= value;
-      if (!isOptional) flatRequired.push(...keys);
-    }
+    processPropertyNames(entry, flat, flatRequired, isOptional);
   }
   if (flatRequired.length) flat.required = [...new Set(flatRequired)];
   return flat;
diff --git a/express-zod-api/tests/json-schema-helpers.spec.ts b/express-zod-api/tests/json-schema-helpers.spec.ts
index df3458fe0..b18c08016 100644
--- a/express-zod-api/tests/json-schema-helpers.spec.ts
+++ b/express-zod-api/tests/json-schema-helpers.spec.ts
@@ -1,7 +1,247 @@
 import { z } from "zod";
-import { flattenIO } from "../src/json-schema-helpers";
+import {
+  flattenIO,
+  isJsonObjectSchema,
+  propsMerger,
+  canMerge,
+  nestOptional,
+  processAllOf,
+  processVariants,
+  processPropertyNames,
+  pullRequestExamples,
+} from "../src/json-schema-helpers";
 
 describe("JSON Schema helpers", () => {
+  describe("isJsonObjectSchema()", () => {
+    test("should return true for object schema", () => {
+      expect(isJsonObjectSchema({ type: "object" })).toBe(true);
+    });
+
+    test.each(["string", "array"] as const)(
+      "should return false for non-object schema",
+      (one) => {
+        expect(isJsonObjectSchema({ type: one })).toBe(false);
+      },
+    );
+  });
+
+  describe("propsMerger()", () => {
+    test("should merge objects deeply", () => {
+      expect(propsMerger({ a: { b: 1 } }, { a: { c: 2 } })).toStrictEqual({
+        a: { b: 1, c: 2 },
+      });
+    });
+
+    test("should throw when leaf values cannot be merged", () => {
+      expect(() => propsMerger({ a: 1 }, { a: "string" })).toThrow(
+        "Can not flatten properties",
+      );
+    });
+  });
+
+  describe("canMerge()", () => {
+    test("should return true for empty object", () => {
+      expect(canMerge({})).toBe(true);
+    });
+
+    test("should return true for object with only mergeable keys", () => {
+      expect(canMerge({ type: "object", properties: {} })).toBe(true);
+    });
+
+    test.each([{ title: "test" }, { format: "date-time" }])(
+      "should return false for object with non-mergeable keys",
+      (subj) => {
+        expect(canMerge(subj)).toBe(false);
+      },
+    );
+  });
+
+  describe("nestOptional()", () => {
+    test("should pair true with given argument", () => {
+      expect(nestOptional({ type: "string" })).toEqual([
+        true,
+        { type: "string" },
+      ]);
+    });
+  });
+
+  describe("processAllOf()", () => {
+    test("should return empty array when no allOf", () => {
+      const result = processAllOf(
+        { type: "object", properties: {} },
+        "coerce",
+        false,
+      );
+      expect(result).toEqual([]);
+    });
+
+    test("should map allOf entries with isOptional flag in coerce mode", () => {
+      const result = processAllOf(
+        {
+          type: "object",
+          allOf: [{ type: "object", properties: { a: { type: "string" } } }],
+        },
+        "coerce",
+        true,
+      );
+      expect(result).toEqual([
+        [true, { type: "object", properties: { a: { type: "string" } } }],
+      ]);
+    });
+
+    test("should throw in throw mode when schema cannot be merged", () => {
+      expect(() =>
+        processAllOf(
+          { type: "object", allOf: [{ type: "string" }] },
+          "throw",
+          false,
+        ),
+      ).toThrow("Can not merge");
+    });
+
+    test("should allow mergeable schemas in throw mode", () => {
+      const result = processAllOf(
+        {
+          type: "object",
+          allOf: [{ type: "object", properties: { a: { type: "string" } } }],
+        },
+        "throw",
+        false,
+      );
+      expect(result).toEqual([
+        [false, { type: "object", properties: { a: { type: "string" } } }],
+      ]);
+    });
+  });
+
+  describe("processVariants()", () => {
+    test("should return empty array when no anyOf/oneOf", () => {
+      const result = processVariants({ type: "object", properties: {} });
+      expect(result).toEqual([]);
+    });
+
+    test("should process anyOf as optional", () => {
+      const result = processVariants({
+        type: "object",
+        anyOf: [{ type: "string" }, { type: "number" }],
+      });
+      expect(result).toEqual([
+        [true, { type: "string" }],
+        [true, { type: "number" }],
+      ]);
+    });
+
+    test("should process oneOf as optional", () => {
+      const result = processVariants({
+        type: "object",
+        oneOf: [{ type: "string" }, { type: "number" }],
+      });
+      expect(result).toEqual([
+        [true, { type: "string" }],
+        [true, { type: "number" }],
+      ]);
+    });
+  });
+
+  describe("processPropertyNames()", () => {
+    test("should not modify flat when no propertyNames", () => {
+      const flat = { type: "object" as const, properties: {} };
+      const flatRequired: string[] = [];
+      processPropertyNames(
+        { type: "object", properties: {} },
+        flat,
+        flatRequired,
+        false,
+      );
+      expect(flat.properties).toEqual({});
+      expect(flatRequired).toEqual([]);
+    });
+
+    test("should extract const key", () => {
+      const flat = { type: "object" as const, properties: {} };
+      const flatRequired: string[] = [];
+      processPropertyNames(
+        { type: "object", propertyNames: { const: "key" } },
+        flat,
+        flatRequired,
+        false,
+      );
+      expect(flat.properties).toHaveProperty("key");
+      expect(flatRequired).toContain("key");
+    });
+
+    test("should extract enum keys", () => {
+      const flat = { type: "object" as const, properties: {} };
+      const flatRequired: string[] = [];
+      processPropertyNames(
+        { type: "object", propertyNames: { enum: ["a", "b"] } },
+        flat,
+        flatRequired,
+        false,
+      );
+      expect(flat.properties).toHaveProperty("a");
+      expect(flat.properties).toHaveProperty("b");
+      expect(flatRequired).toContain("a");
+      expect(flatRequired).toContain("b");
+    });
+
+    test("should not add to required when optional", () => {
+      const flat = { type: "object" as const, properties: {} };
+      const flatRequired: string[] = [];
+      processPropertyNames(
+        { type: "object", propertyNames: { const: "key" } },
+        flat,
+        flatRequired,
+        true,
+      );
+      expect(flat.properties).toHaveProperty("key");
+      expect(flatRequired).toEqual([]);
+    });
+  });
+
+  describe("pullRequestExamples()", () => {
+    test("should return empty array for empty properties", () => {
+      expect(pullRequestExamples({ type: "object", properties: {} })).toEqual(
+        [],
+      );
+    });
+
+    test("should return empty array when properties have no examples", () => {
+      expect(
+        pullRequestExamples({
+          type: "object",
+          properties: { name: { type: "string" } },
+        }),
+      ).toEqual([]);
+    });
+
+    test("should extract examples from properties", () => {
+      expect(
+        pullRequestExamples({
+          type: "object",
+          properties: { name: { type: "string", examples: ["john", "jane"] } },
+        }),
+      ).toEqual([{ name: "john" }, { name: "jane" }]);
+    });
+
+    test("should combine examples from multiple properties", () => {
+      expect(
+        pullRequestExamples({
+          type: "object",
+          properties: {
+            name: { type: "string", examples: ["john", "jane"] },
+            age: { type: "number", examples: [25, 30] },
+          },
+        }),
+      ).toEqual([
+        { name: "john", age: 25 },
+        { name: "john", age: 30 },
+        { name: "jane", age: 25 },
+        { name: "jane", age: 30 },
+      ]);
+    });
+  });
+
   describe("flattenIO()", () => {
     test("should pass the object schema through", () => {
       const subject = flattenIO({