fix(core): use input param for schema serialization

langchain-core/src/output_parsers/tests/structured.test.ts

@@ -210,7 +210,7 @@ describe("StructuredOutputParser.fromZodSchema", () => {
 
     Here is the JSON Schema instance your output must adhere to. Include the enclosing markdown codeblock:
     \`\`\`json
-    {"$schema":"https://json-schema.org/draft/2020-12/schema","type":"object","properties":{"answer":{"description":"answer to the user's question","type":"string"},"sources":{"description":"sources used to answer the question, should be websites.","type":"array","items":{"type":"string"}}},"required":["answer","sources"],"additionalProperties":false}
+    {"$schema":"https://json-schema.org/draft/2020-12/schema","type":"object","properties":{"answer":{"description":"answer to the user's question","type":"string"},"sources":{"type":"array","items":{"type":"string"},"description":"sources used to answer the question, should be websites."}},"required":["answer","sources"],"additionalProperties":false}
     \`\`\`
     "
     `);
@@ -343,7 +343,7 @@ describe("StructuredOutputParser.fromZodSchema", () => {
 
     Here is the JSON Schema instance your output must adhere to. Include the enclosing markdown codeblock:
     \`\`\`json
-    {"$schema":"https://json-schema.org/draft/2020-12/schema","description":"Only One object","type":"object","properties":{"url":{"description":"A link to the resource","type":"string"},"title":{"description":"A title for the resource","type":"string"},"year":{"description":"The year the resource was created","type":"number"},"createdAt":{"description":"The date and time the resource was created","type":"string"},"createdAtDate":{"description":"The date the resource was created","type":"string"},"authors":{"type":"array","items":{"type":"object","properties":{"name":{"description":"The name of the author","type":"string"},"email":{"description":"The email of the author","type":"string"},"type":{"type":"string","enum":["author","editor"]},"address":{"description":"The address of the author","type":"string"},"stateProvince":{"description":"The state or province of the author","type":"string","enum":["AL","AK","AZ"]}},"required":["name","email"],"additionalProperties":false}}},"required":["url","title","year","createdAt","authors"],"additionalProperties":false}
+    {"$schema":"https://json-schema.org/draft/2020-12/schema","type":"object","properties":{"url":{"description":"A link to the resource","type":"string"},"title":{"description":"A title for the resource","type":"string"},"year":{"description":"The year the resource was created","type":"number"},"createdAt":{"description":"The date and time the resource was created","type":"string"},"createdAtDate":{"description":"The date the resource was created","type":"string"},"authors":{"type":"array","items":{"type":"object","properties":{"name":{"description":"The name of the author","type":"string"},"email":{"description":"The email of the author","type":"string"},"type":{"type":"string","enum":["author","editor"]},"address":{"description":"The address of the author","type":"string"},"stateProvince":{"description":"The state or province of the author","type":"string","enum":["AL","AK","AZ"]}},"required":["name","email"],"additionalProperties":false}}},"required":["url","title","year","createdAt","authors"],"additionalProperties":false,"description":"Only One object"}
     \`\`\`
     "
     `);

langchain-core/src/utils/json_schema.ts

@@ -1,7 +1,15 @@
 import { toJSONSchema } from "zod/v4/core";
 import { type JsonSchema7Type, zodToJsonSchema } from "zod-to-json-schema";
 import { dereference, type Schema } from "@cfworker/json-schema";
-import { isZodSchemaV3, isZodSchemaV4, InteropZodType } from "./types/zod.js";
+import {
+  isZodSchemaV3,
+  isZodSchemaV4,
+  InteropZodType,
+  interopZodObjectStrict,
+  isZodObjectV4,
+  ZodObjectV4,
+  interopZodTransformInputSchema,
+} from "./types/zod.js";
 
 export type JSONSchema = JsonSchema7Type;
 
@@ -14,7 +22,16 @@ export { deepCompareStrict, Validator } from "@cfworker/json-schema";
  */
 export function toJsonSchema(schema: InteropZodType | JSONSchema): JSONSchema {
   if (isZodSchemaV4(schema)) {
-    return toJSONSchema(schema);
+    const inputSchema = interopZodTransformInputSchema(schema);
+    if (isZodObjectV4(inputSchema)) {
+      const strictSchema = interopZodObjectStrict(
+        inputSchema,
+        true
+      ) as ZodObjectV4;
+      return toJSONSchema(strictSchema);
+    } else {
+      return toJSONSchema(schema);
+    }
   }
   if (isZodSchemaV3(schema)) {
     return zodToJsonSchema(schema);

langchain-core/src/utils/tests/json_schema.test.ts

@@ -0,0 +1,34 @@
+import { describe, it, expect } from "@jest/globals";
+import { z as z4 } from "zod/v4";
+import { toJsonSchema } from "../json_schema.js";
+
+describe("toJsonSchema", () => {
+  describe("with zod v4 schemas", () => {
+    // https://github.com/langchain-ai/langchainjs/issues/8367
+    it("should allow transformed v4 zod schemas", () => {
+      const schema = z4
+        .object({
+          name: z4.string(),
+          age: z4.number(),
+        })
+        .describe("Object description")
+        .transform((data) => ({
+          ...data,
+          upperName: data.name.toUpperCase(),
+          doubledAge: data.age * 2,
+        }));
+      const jsonSchema = toJsonSchema(schema);
+      expect(jsonSchema).toEqual({
+        $schema: "https://json-schema.org/draft/2020-12/schema",
+        type: "object",
+        description: "Object description",
+        properties: {
+          name: { type: "string" },
+          age: { type: "number" },
+        },
+        required: ["name", "age"],
+        additionalProperties: false,
+      });
+    });
+  });
+});