diff --git a/packages/core/src/tool.ts b/packages/core/src/tool.ts
index 1e46a289fec..5e2ca8401aa 100644
--- a/packages/core/src/tool.ts
+++ b/packages/core/src/tool.ts
@@ -308,7 +308,7 @@ function registrationError(tool: Tool.Info) {
     if (error) return error
   }
   const name = normalizedName(tool)
-  if (!/^[A-Za-z0-9_-]{1,64}$/.test(name)) return new RegistrationError({ name, message: `Invalid tool name: ${name}` })
+  if (!/^[A-Za-z0-9_-]{1,128}$/.test(name)) return new RegistrationError({ name, message: `Invalid tool name: ${name}` })
   const id = effectiveName(tool)
   if (tool.options?.codemode === false && id === "execute")
     return new RegistrationError({ name: id, message: 'Tool name "execute" is reserved for CodeMode' })
diff --git a/packages/core/test/mcp.test.ts b/packages/core/test/mcp.test.ts
index 330abe21238..f37ec6a9553 100644
--- a/packages/core/test/mcp.test.ts
+++ b/packages/core/test/mcp.test.ts
@@ -2117,7 +2117,7 @@ testEffect(Layer.empty).live("isolates invalid MCP tools and preserves plugin tr
       }) satisfies Mcp.Tool
     const healthy = [tool("demo", "search"), tool("other", "lookup")]
     const namespace = tool("x".repeat(65), "lookup")
-    const catalog = yield* Ref.make([tool("demo", "x".repeat(65)), ...healthy, namespace])
+    const catalog = yield* Ref.make([tool("demo", "x".repeat(129)), ...healthy, namespace])
 
     yield* Effect.gen(function* () {
       const registry = yield* Tool.Service
@@ -2146,7 +2146,7 @@ testEffect(Layer.empty).live("isolates invalid MCP tools and preserves plugin tr
         editor.remove("repaired_lookup")
       })
 
-      yield* Ref.set(catalog, [tool("demo", "y".repeat(65)), ...healthy, tool("demo", "added"), namespace])
+      yield* Ref.set(catalog, [tool("demo", "y".repeat(129)), ...healthy, tool("demo", "added"), namespace])
       yield* bus.publish(McpEvent.ToolsChanged, { server: "demo" })
       yield* waitForTool(registry, "demo_added")
       expect((yield* toolDefinitions(registry)).map((tool) => tool.name)).toEqual([
diff --git a/packages/core/test/tool-registry.test.ts b/packages/core/test/tool-registry.test.ts
index 2c3e74dace7..f77e05a6630 100644
--- a/packages/core/test/tool-registry.test.ts
+++ b/packages/core/test/tool-registry.test.ts
@@ -329,7 +329,7 @@ describe("Tool", () => {
         {
           before: make(),
           "": make(),
-          ["x".repeat(65)]: make(),
+          ["x".repeat(129)]: make(),
           "echo.tool": constant("first"),
           echo_tool: constant("last"),
           execute: make(),
@@ -346,6 +346,27 @@ describe("Tool", () => {
     }),
   )
 
+  it.effect("registers 128-character MCP tool names in Code Mode", () =>
+    Effect.gen(function* () {
+      const service = yield* Tool.Service
+      const name = "x".repeat(128)
+      yield* transform(service, { [name]: make(), ["x".repeat(129)]: make() }, { namespace: "cloudflare" })
+
+      const snapshot = yield* service.snapshot()
+      expect(codeModeListings(snapshot.codeModeCatalog!).map((tool) => tool.path)).toEqual([`cloudflare.${name}`])
+      const result = yield* snapshot.execute({
+        ...call("execute"),
+        call: {
+          type: "tool-call",
+          id: "call-long-mcp-name",
+          name: "execute",
+          input: { code: `return (await tools.cloudflare[${JSON.stringify(name)}]({ text: "hello" })).text` },
+        },
+      })
+      expect(result.content).toEqual([{ type: "text", text: "hello" }])
+    }),
+  )
+
   it.effect("executes native tools without requiring letter-leading names or namespace segments", () =>
     Effect.gen(function* () {
       const service = yield* Tool.Service