diff --git a/apps/server/src/mcp/McpHttpServer.ts b/apps/server/src/mcp/McpHttpServer.ts
index 5a4e62e3b241..84535b3cb4e1 100644
--- a/apps/server/src/mcp/McpHttpServer.ts
+++ b/apps/server/src/mcp/McpHttpServer.ts
@@ -35,6 +35,7 @@ import {
   MAX_REPORTED_DEPTH,
   toolOutcome,
 } from "../telemetry/ProviderDimensions.ts";
+import { advertisedJsonSchema } from "./advertisedJsonSchema.ts";
 import * as McpInvocationContext from "./McpInvocationContext.ts";
 import * as McpToolAccess from "./McpToolAccess.ts";
 import * as OrchestratorMcpService from "./OrchestratorMcpService.ts";
@@ -448,7 +449,7 @@ const registerPreviewSnapshot = Effect.fn("McpHttpServer.registerPreviewSnapshot
     tool: new McpSchema.Tool({
       name: tool.name,
       description: Tool.getDescription(tool),
-      inputSchema: Tool.getJsonSchema(tool),
+      inputSchema: advertisedJsonSchema(tool),
       annotations: {
         ...Context.getOption(tool.annotations, Tool.Title).pipe(
           Option.map((title) => ({ title })),
@@ -632,7 +633,7 @@ const registerImageTool = Effect.fn("McpHttpServer.registerImageTool")(function*
     tool: new McpSchema.Tool({
       name: tool.name,
       description: Tool.getDescription(tool),
-      inputSchema: Tool.getJsonSchema(tool),
+      inputSchema: advertisedJsonSchema(tool),
       annotations: {
         ...Context.getOption(tool.annotations, Tool.Title).pipe(
           Option.map((title) => ({ title })),
diff --git a/apps/server/src/mcp/advertisedJsonSchema.test.ts b/apps/server/src/mcp/advertisedJsonSchema.test.ts
new file mode 100644
index 000000000000..de72d6393029
--- /dev/null
+++ b/apps/server/src/mcp/advertisedJsonSchema.test.ts
@@ -0,0 +1,50 @@
+import { expect, it } from "@effect/vitest";
+import * as Schema from "effect/Schema";
+import { Tool } from "effect/ai";
+
+import { advertisedJsonSchema } from "./advertisedJsonSchema.ts";
+
+it("drops JSON noise but keeps null where it is required", () => {
+  const Every = Schema.Struct({ ms: Schema.Int });
+  const tool = Tool.make("example", {
+    parameters: Schema.Struct({
+      threadId: Schema.optional(Schema.NullOr(Schema.String)),
+      beforeRunId: Schema.NullOr(Schema.String),
+      limit: Schema.optional(Schema.Int),
+      every: Schema.Union([Every, Schema.fromJsonString(Every)]),
+      target: Schema.optional(
+        Schema.NullOr(
+          Schema.Union([
+            Schema.Struct({ kind: Schema.Literal("url"), url: Schema.String }),
+            Schema.Struct({ kind: Schema.Literal("number"), number: Schema.Int }),
+          ]),
+        ),
+      ),
+    }),
+  });
+
+  expect(advertisedJsonSchema(tool)).toEqual({
+    type: "object",
+    properties: {
+      threadId: { type: "string" },
+      beforeRunId: { anyOf: [{ type: "string" }, { type: "null" }] },
+      limit: { type: "integer" },
+      every: { type: "object", properties: { ms: { type: "integer" } }, required: ["ms"] },
+      target: {
+        anyOf: [
+          {
+            type: "object",
+            properties: { kind: { type: "string", enum: ["url"] }, url: { type: "string" } },
+            required: ["kind", "url"],
+          },
+          {
+            type: "object",
+            properties: { kind: { type: "string", enum: ["number"] }, number: { type: "integer" } },
+            required: ["kind", "number"],
+          },
+        ],
+      },
+    },
+    required: ["beforeRunId", "every"],
+  });
+});
diff --git a/apps/server/src/mcp/advertisedJsonSchema.ts b/apps/server/src/mcp/advertisedJsonSchema.ts
new file mode 100644
index 000000000000..f1193bd7739c
--- /dev/null
+++ b/apps/server/src/mcp/advertisedJsonSchema.ts
@@ -0,0 +1,59 @@
+import * as Predicate from "effect/Predicate";
+import { Tool } from "effect/ai";
+
+type Json = unknown;
+type JsonObject = { [key: string]: Json };
+
+const isNullSchema = (value: Json) =>
+  Predicate.isObject(value) && value.type === "null" && Object.keys(value).length === 1;
+
+const isBareAnyOf = (value: Json): value is { anyOf: Array<Json> } =>
+  Predicate.isObject(value) && Array.isArray(value.anyOf) && Object.keys(value).length === 1;
+
+// A `Schema.fromJsonString` fallback. Advertised beside object shapes, it invites stringified input.
+const isJsonStringSchema = (value: Json) =>
+  Predicate.isObject(value) &&
+  value.type === "string" &&
+  value.contentMediaType === "application/json";
+
+const SAFE_INTEGER_BOUNDS: Record<string, number> = {
+  maximum: Number.MAX_SAFE_INTEGER,
+  minimum: Number.MIN_SAFE_INTEGER,
+};
+
+const compact = (schema: Json, optional: boolean): Json => {
+  if (Array.isArray(schema)) return schema.map((item) => compact(item, false));
+  if (!Predicate.isObject(schema)) return schema;
+  const required = new Set(Array.isArray(schema.required) ? schema.required : []);
+  let result: JsonObject = {};
+  for (const [key, value] of Object.entries(schema)) {
+    if (key === "additionalProperties" && value === true) continue;
+    if (SAFE_INTEGER_BOUNDS[key] === value) continue;
+    result[key] =
+      key === "properties" && Predicate.isObject(value)
+        ? Object.fromEntries(
+            Object.entries(value).map(([name, property]) => [
+              name,
+              compact(property, !required.has(name)),
+            ]),
+          )
+        : compact(value, false);
+  }
+  if (Array.isArray(result.anyOf)) {
+    const branches = result.anyOf
+      .flatMap((branch) => (isBareAnyOf(branch) ? branch.anyOf : [branch]))
+      .filter((branch) => !(optional && isNullSchema(branch)) && !isJsonStringSchema(branch));
+    const { anyOf: _anyOf, ...rest } = result;
+    const only = branches.length === 1 ? branches[0] : undefined;
+    result = Predicate.isObject(only) ? { ...only, ...rest } : { ...rest, anyOf: branches };
+  }
+  return result;
+};
+
+/**
+ * The input schema T3 advertises for a tool. Drops JSON noise that every thread pays for:
+ * `additionalProperties: true`, safe-integer bounds, nested `anyOf`, JSON-string fallbacks, and
+ * the `null` branch of optional properties. Decoding still uses the full schema.
+ */
+export const advertisedJsonSchema = (tool: Tool.Any) =>
+  compact(Tool.getJsonSchema(tool), false) as ReturnType<typeof Tool.getJsonSchema>;
diff --git a/packages/contracts/src/scheduledTask.ts b/packages/contracts/src/scheduledTask.ts
index 5d8e4d29d68a..b4dffacd74c0 100644
--- a/packages/contracts/src/scheduledTask.ts
+++ b/packages/contracts/src/scheduledTask.ts
@@ -66,7 +66,7 @@ export const MAX_WEBHOOK_DELIVERY_AGE_MINUTES = 24 * 60;
 const WebhookMaxDeliveryAgeMinutes = Schema.Int.check(
   Schema.isBetween({ minimum: 1, maximum: MAX_WEBHOOK_DELIVERY_AGE_MINUTES }),
 ).annotate({
-  description: "Skip requests held offline over this many minutes. Null: run all.",
+  description: "Skip requests held offline over this many minutes. Omit to run all.",
 });
 
 export function isWebhookDedupeTemplate(template: string): boolean {
@@ -152,7 +152,7 @@ const ScheduledTaskUpsertWebhookSchedule = Schema.Struct({
       }),
     ),
   ).annotate({
-    description: "Null or omitted: URL token only.",
+    description: "Omit for URL token only.",
   }),
   maxDeliveryAgeMinutes: Schema.optional(Schema.NullOr(WebhookMaxDeliveryAgeMinutes)),
   dedupe: Schema.optional(ScheduledTaskWebhookDedupe),