diff --git a/src/server/toolRegistrationOptions.ts b/src/server/toolRegistrationOptions.ts
index 5bf6a2788..49e13e43b 100644
--- a/src/server/toolRegistrationOptions.ts
+++ b/src/server/toolRegistrationOptions.ts
@@ -2,6 +2,15 @@ import { z } from "zod";
 
 import type { ToolContract } from "../contracts/toolContracts.js";
 
+const ADVERTISED_INPUT_SCHEMAS = new WeakMap<
+  z.ZodObject,
+  Readonly<Record<string, unknown>>
+>();
+const ADVERTISED_OUTPUT_SCHEMAS = new WeakMap<
+  z.ZodObject,
+  Readonly<Record<string, unknown>>
+>();
+
 /** Project the public contract fields accepted by MCP tool registration. */
 export const toolRegistrationOptions = (contract: ToolContract) => ({
   title: contract.title,
@@ -22,10 +31,8 @@ const advertisedInputSchema = (schema: z.ZodObject) => ({
     vendor: "rea",
     validate: (input: unknown) => ({ value: input }),
     jsonSchema: {
-      input: () =>
-        describeProperties(closeObjectSchemas(inputJsonSchema(schema))),
-      output: () =>
-        describeProperties(closeObjectSchemas(inputJsonSchema(schema))),
+      input: () => advertisedInputJsonSchema(schema),
+      output: () => advertisedInputJsonSchema(schema),
     },
   },
 });
@@ -41,19 +48,42 @@ const advertisedOutputSchema = (schema: z.ZodObject) => {
     "~standard": {
       ...standard,
       jsonSchema: {
-        input: () =>
-          describeRootProperties(
-            closeObjectSchemas(converter({ target: "draft-2020-12" })),
-          ),
-        output: () =>
-          describeRootProperties(
-            closeObjectSchemas(converter({ target: "draft-2020-12" })),
-          ),
+        input: () => advertisedOutputJsonSchema(schema, converter),
+        output: () => advertisedOutputJsonSchema(schema, converter),
       },
     },
   };
 };
 
+const advertisedInputJsonSchema = (
+  schema: z.ZodObject,
+): Readonly<Record<string, unknown>> =>
+  cachedJsonSchema(ADVERTISED_INPUT_SCHEMAS, schema, () =>
+    describeProperties(closeObjectSchemas(inputJsonSchema(schema))),
+  );
+
+const advertisedOutputJsonSchema = (
+  schema: z.ZodObject,
+  converter: NonNullable<z.ZodObject["~standard"]["jsonSchema"]>["output"],
+): Readonly<Record<string, unknown>> =>
+  cachedJsonSchema(ADVERTISED_OUTPUT_SCHEMAS, schema, () =>
+    describeRootProperties(
+      closeObjectSchemas(converter({ target: "draft-2020-12" })),
+    ),
+  );
+
+const cachedJsonSchema = (
+  cache: WeakMap<z.ZodObject, Readonly<Record<string, unknown>>>,
+  schema: z.ZodObject,
+  create: () => Record<string, unknown>,
+): Readonly<Record<string, unknown>> => {
+  const cached = cache.get(schema);
+  if (cached !== undefined) return cached;
+  const created = create();
+  cache.set(schema, created);
+  return created;
+};
+
 const inputJsonSchema = (schema: z.ZodObject): Record<string, unknown> => {
   const converter = schema["~standard"].jsonSchema?.input;
   if (converter === undefined)
diff --git a/tests/contractSnapshot.test.ts b/tests/contractSnapshot.test.ts
index 833c0943b..964012325 100644
--- a/tests/contractSnapshot.test.ts
+++ b/tests/contractSnapshot.test.ts
@@ -62,6 +62,21 @@ const emptySchemaPaths = (value: unknown, path = "$"): string[] => {
 };
 
 describe("tool contract surface", () => {
+  it("reuses finalized advertised schemas", () => {
+    const contract = TOOL_CONTRACTS[0];
+    expect(contract).toBeDefined();
+    if (contract === undefined) return;
+
+    const first = toolRegistrationOptions(contract);
+    const second = toolRegistrationOptions(contract);
+    expect(first.inputSchema["~standard"].jsonSchema.input()).toBe(
+      second.inputSchema["~standard"].jsonSchema.output(),
+    );
+    expect(first.outputSchema["~standard"].jsonSchema.input()).toBe(
+      second.outputSchema["~standard"].jsonSchema.output(),
+    );
+  });
+
   it("gives fallback parameter guidance operational meaning", () => {
     const contract = TOOL_CONTRACTS.find(
       ({ name }) => name === "analyze_function",