diff --git a/src/plugin/normalize-tool-arg-schemas.test.ts b/src/plugin/normalize-tool-arg-schemas.test.ts
new file mode 100644
index 0000000000..27f1489958
--- /dev/null
+++ b/src/plugin/normalize-tool-arg-schemas.test.ts
@@ -0,0 +1,97 @@
+/// <reference types="bun-types" />
+
+import { afterEach, describe, expect, it } from "bun:test"
+import { cpSync, mkdtempSync, rmSync } from "node:fs"
+import { tmpdir } from "node:os"
+import { dirname, join } from "node:path"
+import { pathToFileURL } from "node:url"
+import { tool } from "@opencode-ai/plugin"
+import { normalizeToolArgSchemas } from "./normalize-tool-arg-schemas"
+
+const tempDirectories: string[] = []
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null
+}
+
+function getNestedRecord(record: Record<string, unknown>, key: string): Record<string, unknown> | undefined {
+  const value = record[key]
+  return isRecord(value) ? value : undefined
+}
+
+async function loadSeparateHostZodModule(): Promise<typeof import("zod")> {
+  const pluginPackageDirectory = dirname(Bun.resolveSync("@opencode-ai/plugin/package.json", import.meta.dir))
+  const sourceZodDirectory = join(pluginPackageDirectory, "node_modules", "zod")
+  const tempDirectory = mkdtempSync(join(tmpdir(), "omo-host-zod-"))
+  const copiedZodDirectory = join(tempDirectory, "zod")
+
+  cpSync(sourceZodDirectory, copiedZodDirectory, { recursive: true })
+  tempDirectories.push(tempDirectory)
+
+  return await import(pathToFileURL(join(copiedZodDirectory, "index.js")).href)
+}
+
+function serializeWithHostZod(
+  hostZod: typeof import("zod"),
+  args: Record<string, object>,
+): Record<string, unknown> {
+  return hostZod.z.toJSONSchema(Reflect.apply(hostZod.z.object, hostZod.z, [args]))
+}
+
+describe("normalizeToolArgSchemas", () => {
+  afterEach(() => {
+    for (const tempDirectory of tempDirectories.splice(0)) {
+      rmSync(tempDirectory, { recursive: true, force: true })
+    }
+  })
+
+  it("preserves nested descriptions and metadata across zod instances", async () => {
+    // given
+    const hostZod = await loadSeparateHostZodModule()
+    const toolDefinition = tool({
+      description: "Search tool",
+      args: {
+        filters: tool.schema
+          .object({
+            query: tool.schema
+              .string()
+              .describe("Free-text search query")
+              .meta({ title: "Query", examples: ["issue 2314"] }),
+          })
+          .describe("Filter options")
+          .meta({ title: "Filters" }),
+      },
+      async execute(): Promise<string> {
+        return "ok"
+      },
+    })
+
+    // when
+    const beforeSchema = serializeWithHostZod(hostZod, toolDefinition.args)
+    const beforeProperties = getNestedRecord(beforeSchema, "properties")
+    const beforeFilters = beforeProperties ? getNestedRecord(beforeProperties, "filters") : undefined
+    const beforeFilterProperties = beforeFilters ? getNestedRecord(beforeFilters, "properties") : undefined
+    const beforeQuery = beforeFilterProperties ? getNestedRecord(beforeFilterProperties, "query") : undefined
+
+    normalizeToolArgSchemas(toolDefinition)
+
+    const afterSchema = serializeWithHostZod(hostZod, toolDefinition.args)
+    const afterProperties = getNestedRecord(afterSchema, "properties")
+    const afterFilters = afterProperties ? getNestedRecord(afterProperties, "filters") : undefined
+    const afterFilterProperties = afterFilters ? getNestedRecord(afterFilters, "properties") : undefined
+    const afterQuery = afterFilterProperties ? getNestedRecord(afterFilterProperties, "query") : undefined
+
+    // then
+    expect(beforeFilters?.description).toBeUndefined()
+    expect(beforeFilters?.title).toBeUndefined()
+    expect(beforeQuery?.description).toBeUndefined()
+    expect(beforeQuery?.title).toBeUndefined()
+    expect(beforeQuery?.examples).toBeUndefined()
+
+    expect(afterFilters?.description).toBe("Filter options")
+    expect(afterFilters?.title).toBe("Filters")
+    expect(afterQuery?.description).toBe("Free-text search query")
+    expect(afterQuery?.title).toBe("Query")
+    expect(afterQuery?.examples).toEqual(["issue 2314"])
+  })
+})
diff --git a/src/plugin/normalize-tool-arg-schemas.ts b/src/plugin/normalize-tool-arg-schemas.ts
new file mode 100644
index 0000000000..4e8182b637
--- /dev/null
+++ b/src/plugin/normalize-tool-arg-schemas.ts
@@ -0,0 +1,42 @@
+import { tool } from "@opencode-ai/plugin"
+import type { ToolDefinition } from "@opencode-ai/plugin"
+
+type ToolArgSchema = ToolDefinition["args"][string]
+
+type SchemaWithJsonSchemaOverride = ToolArgSchema & {
+  _zod: ToolArgSchema["_zod"] & {
+    toJSONSchema?: () => unknown
+  }
+}
+
+function stripRootJsonSchemaFields(jsonSchema: Record<string, unknown>): Record<string, unknown> {
+  const { $schema: _schema, ...rest } = jsonSchema
+  return rest
+}
+
+function attachJsonSchemaOverride(schema: SchemaWithJsonSchemaOverride): void {
+  if (schema._zod.toJSONSchema) {
+    return
+  }
+
+  schema._zod.toJSONSchema = (): Record<string, unknown> => {
+    const originalOverride = schema._zod.toJSONSchema
+    delete schema._zod.toJSONSchema
+
+    try {
+      return stripRootJsonSchemaFields(tool.schema.toJSONSchema(schema))
+    } finally {
+      schema._zod.toJSONSchema = originalOverride
+    }
+  }
+}
+
+export function normalizeToolArgSchemas<TDefinition extends Pick<ToolDefinition, "args">>(
+  toolDefinition: TDefinition,
+): TDefinition {
+  for (const schema of Object.values(toolDefinition.args)) {
+    attachJsonSchemaOverride(schema)
+  }
+
+  return toolDefinition
+}
diff --git a/src/plugin/tool-registry.ts b/src/plugin/tool-registry.ts
index 3b441c1970..a08b9bd33a 100644
--- a/src/plugin/tool-registry.ts
+++ b/src/plugin/tool-registry.ts
@@ -32,6 +32,7 @@ import { log } from "../shared"
 
 import type { Managers } from "../create-managers"
 import type { SkillContext } from "./skill-context"
+import { normalizeToolArgSchemas } from "./normalize-tool-arg-schemas"
 
 export type ToolRegistryResult = {
   filteredTools: ToolsRecord
@@ -139,6 +140,10 @@ export function createToolRegistry(args: {
     ...hashlineToolsRecord,
   }
 
+  for (const toolDefinition of Object.values(allTools)) {
+    normalizeToolArgSchemas(toolDefinition)
+  }
+
   const filteredTools = filterDisabledTools(allTools, pluginConfig.disabled_tools)
 
   return {