diff --git a/packages/core/src/mcp/guidance.ts b/packages/core/src/mcp/guidance.ts
index 2e7f34b0474e..d5eae0f3a498 100644
--- a/packages/core/src/mcp/guidance.ts
+++ b/packages/core/src/mcp/guidance.ts
@@ -17,7 +17,7 @@ type Summary = typeof Summary.Type
 const entries = (servers: ReadonlyArray<Summary>) =>
   servers.flatMap((server) => [
     `  <server name="${server.server}">`,
-    `    Use tools from this server through \`execute\` under \`tools[${JSON.stringify(McpTool.group(server.server))}]\`.`,
+    `    Use tools from this server through \`execute\` under \`tools[${JSON.stringify(McpTool.namespace(server.server))}]\`.`,
     ...server.instructions.split("\n").map((line) => `    ${line}`),
     "  </server>",
   ])
diff --git a/packages/core/src/plugin/host.ts b/packages/core/src/plugin/host.ts
index 007a53ed70ec..e799a22217c9 100644
--- a/packages/core/src/plugin/host.ts
+++ b/packages/core/src/plugin/host.ts
@@ -305,27 +305,13 @@ export const make = Effect.fn("PluginHost.make")(function* (plugin: PluginV2.Int
         }),
     },
     tool: {
+      // The tool domain is scoped registration, not State, so the host adapts the draft to register calls directly.
       transform: (callback) =>
-        Effect.gen(function* () {
-          const registrations: Array<{
-            readonly name: string
-            readonly tool: Tool.AnyTool
-            readonly options?: Tool.RegisterOptions
-          }> = []
-          yield* Effect.sync(() =>
-            callback({
-              add: (name, tool, options) => {
-                registrations.push({ name, tool, ...(options ? { options } : {}) })
-              },
-            }),
-          )
-          yield* Effect.forEach(
-            registrations,
-            (registration) => tools.register({ [registration.name]: registration.tool }, registration.options),
-            { discard: true },
-          ).pipe(Effect.orDie)
-          return { dispose: Effect.void }
-        }),
+        Effect.forEach(
+          Tool.fromDraft(callback),
+          ({ name, tool, options }) => tools.register({ [name]: tool }, options),
+          { discard: true },
+        ).pipe(Effect.orDie, Effect.as({ dispose: Effect.void })),
       hook: (name, callback) => {
         if (name === "execute.before") {
           return toolHooks.hook.before((event) => {
diff --git a/packages/core/src/plugin/promise.ts b/packages/core/src/plugin/promise.ts
index 75c8b300afdf..7a1dcab839de 100644
--- a/packages/core/src/plugin/promise.ts
+++ b/packages/core/src/plugin/promise.ts
@@ -154,7 +154,11 @@ export function fromPromise(plugin: Plugin) {
               register(
                 host.tool.transform((draft) =>
                   callback({
-                    add: (tool: AnyTool) => draft.add(tool.name, fromPromiseTool(tool), tool.options),
+                    add: (tool: AnyTool) =>
+                      draft.add(tool.name, fromPromiseTool(tool), {
+                        ...(tool.namespace !== undefined ? { namespace: tool.namespace } : {}),
+                        ...(tool.codemode !== undefined ? { codemode: tool.codemode } : {}),
+                      }),
                   }),
                 ),
               ),
diff --git a/packages/core/src/tool/AGENTS.md b/packages/core/src/tool/AGENTS.md
index 08c9fabefe2d..4e4a1b91e65c 100644
--- a/packages/core/src/tool/AGENTS.md
+++ b/packages/core/src/tool/AGENTS.md
@@ -29,8 +29,8 @@ Leaves own resolution, permission, and side-effect ordering. Translate only expe
 ## Registration
 
 Built-ins and plugin tools register through `Tools.Service.register({ [name]: tool })`. Registrations may provide a
-group, which flattens direct model names to `<group>_<tool>`, and default into CodeMode (`codemode` defaults true;
-`codemode: false` keeps the tool on the provider's native tool list).
+`namespace`, which flattens native model names to `<namespace>_<tool>`, and default into CodeMode (`codemode` defaults
+true; `codemode: false` keeps the tool on the provider's native tool list).
 
 Registrations are scoped:
 
diff --git a/packages/core/src/tool/execute.ts b/packages/core/src/tool/execute.ts
index 89672dbfc6c9..56b4eb5e832e 100644
--- a/packages/core/src/tool/execute.ts
+++ b/packages/core/src/tool/execute.ts
@@ -39,7 +39,7 @@ type CollectedFiles = {
 interface Registration {
   readonly tool: AnyTool
   readonly name: string
-  readonly group?: string
+  readonly namespace?: string
 }
 
 export const create = (registrations: ReadonlyMap<string, Registration>) => {
@@ -56,19 +56,19 @@ export const create = (registrations: ReadonlyMap<string, Registration>) => {
         output: child.outputSchema,
         run: (input) => invoke(name, registration, input),
       })
-      if (registration.group === undefined) {
+      if (registration.namespace === undefined) {
         const path = registration.name
         if (Object.hasOwn(tools, path)) throw new TypeError(`CodeMode tool namespace conflict: ${path}`)
         tools[path] = value
         continue
       }
       const path = registration.name
-      const namespace = registration.group
-      const group = tools[namespace]
-      if (group && Tool.isDefinition(group)) throw new TypeError(`CodeMode tool namespace conflict: ${namespace}`)
-      if (group) {
-        if (Object.hasOwn(group, path)) throw new TypeError(`CodeMode tool namespace conflict: ${namespace}.${path}`)
-        group[path] = value
+      const namespace = registration.namespace
+      const branch = tools[namespace]
+      if (branch && Tool.isDefinition(branch)) throw new TypeError(`CodeMode tool namespace conflict: ${namespace}`)
+      if (branch) {
+        if (Object.hasOwn(branch, path)) throw new TypeError(`CodeMode tool namespace conflict: ${namespace}.${path}`)
+        branch[path] = value
         continue
       }
       const entries: Record<string, Tool.Definition<never>> = {}
diff --git a/packages/core/src/tool/mcp.ts b/packages/core/src/tool/mcp.ts
index 8aad746ed627..3562fbc8c371 100644
--- a/packages/core/src/tool/mcp.ts
+++ b/packages/core/src/tool/mcp.ts
@@ -13,10 +13,10 @@ import { Tools } from "./tools"
 import { ToolRegistry } from "./registry"
 
 /**
- * Registry group and permission action names for MCP tools.
+ * Registry namespace and permission action names for MCP tools.
  */
-export const group = (server: string) => server.replace(/[^a-zA-Z0-9_-]/g, "_")
-export const name = (server: string, tool: string) => `${group(server)}_${tool.replace(/[^a-zA-Z0-9_-]/g, "_")}`
+export const namespace = (server: string) => server.replace(/[^a-zA-Z0-9_-]/g, "_")
+export const name = (server: string, tool: string) => `${namespace(server)}_${tool.replace(/[^a-zA-Z0-9_-]/g, "_")}`
 
 export const layer = Layer.effectDiscard(
   Effect.gen(function* () {
@@ -32,11 +32,11 @@ export const layer = Layer.effectDiscard(
     // registry never has a gap where MCP tools disappear mid-swap.
     const reconcile = lock.withPermit(
       Effect.gen(function* () {
-        const groups = new Map<string, Record<string, Tool.AnyTool>>()
+        const byServer = new Map<string, Record<string, Tool.AnyTool>>()
         for (const tool of yield* mcp.tools()) {
-          const group = groups.get(tool.server) ?? {}
+          const record = byServer.get(tool.server) ?? {}
           const schema = (tool.inputSchema ?? {}) as JsonSchema.JsonSchema
-          group[tool.name] = Tool.withPermission(
+          record[tool.name] = Tool.withPermission(
             Tool.make({
               description: tool.description ?? "",
               jsonSchema: {
@@ -102,16 +102,12 @@ export const layer = Layer.effectDiscard(
             }),
             name(tool.server, tool.name),
           )
-          groups.set(tool.server, group)
+          byServer.set(tool.server, record)
         }
         const next = yield* Scope.fork(scope)
-        yield* Effect.forEach(
-          groups,
-          ([group, record]) => tools.register(record, { group }),
-          {
-            discard: true,
-          },
-        ).pipe(Scope.provide(next), Effect.orDie)
+        yield* Effect.forEach(byServer, ([server, record]) => tools.register(record, { namespace: server }), {
+          discard: true,
+        }).pipe(Scope.provide(next), Effect.orDie)
         if (current) yield* Scope.close(current, Exit.void)
         current = next
       }),
diff --git a/packages/core/src/tool/registry.ts b/packages/core/src/tool/registry.ts
index b1087c782284..b058738016e5 100644
--- a/packages/core/src/tool/registry.ts
+++ b/packages/core/src/tool/registry.ts
@@ -54,7 +54,7 @@ const registryLayer = Layer.effect(
     type Registration = {
       readonly tool: AnyTool
       readonly name: string
-      readonly group?: string
+      readonly namespace?: string
       readonly codemode: boolean
     }
     const local = new Map<string, Array<{ readonly token: object; readonly registration: Registration }>>()
@@ -129,7 +129,7 @@ const registryLayer = Layer.effect(
 
     return Service.of({
       register: Effect.fn("ToolRegistry.register")(function* (tools, options) {
-        const entries = registrationEntries(tools, options?.group)
+        const entries = registrationEntries(tools, options?.namespace)
         if (entries.length === 0) return
         const codemode = options?.codemode ?? true
         const reserved = codemode ? undefined : entries.find((entry) => entry.key === "execute")
@@ -148,7 +148,7 @@ const registryLayer = Layer.effect(
                   registration: {
                     tool: entry.tool,
                     name: entry.name,
-                    group: entry.group,
+                    namespace: entry.namespace,
                     codemode,
                   },
                 },
diff --git a/packages/core/test/lib/tool.ts b/packages/core/test/lib/tool.ts
index 10d68c7fa384..0de44d0b7fa2 100644
--- a/packages/core/test/lib/tool.ts
+++ b/packages/core/test/lib/tool.ts
@@ -46,24 +46,11 @@ export const registerToolPlugin = <R>(plugin: {
     const context = host({
       tool: {
         transform: (callback) =>
-          Effect.gen(function* () {
-            const registrations: Array<{
-              readonly name: string
-              readonly tool: Tool.AnyTool
-              readonly options?: Tool.RegisterOptions
-            }> = []
-            callback({
-              add: (name, tool, options) => {
-                registrations.push({ name, tool, ...(options ? { options } : {}) })
-              },
-            })
-            yield* Effect.forEach(
-              registrations,
-              (registration) => tools.register({ [registration.name]: registration.tool }, registration.options),
-              { discard: true },
-            ).pipe(Effect.orDie)
-            return { dispose: Effect.void }
-          }),
+          Effect.forEach(
+            Tool.fromDraft(callback),
+            ({ name, tool, options }) => tools.register({ [name]: tool }, options),
+            { discard: true },
+          ).pipe(Effect.orDie, Effect.as({ dispose: Effect.void })),
         hook: () => Effect.die("registerToolPlugin does not support tool hooks"),
       },
     })
diff --git a/packages/core/test/plugin.test.ts b/packages/core/test/plugin.test.ts
index 6d9e0aac3dc5..49b2735147b6 100644
--- a/packages/core/test/plugin.test.ts
+++ b/packages/core/test/plugin.test.ts
@@ -274,7 +274,7 @@ describe("PluginV2", () => {
     }),
   )
 
-  it.effect("groups tool names and routes codemode registrations through execute", () =>
+  it.effect("namespaces tool names and routes codemode registrations through execute", () =>
     Effect.gen(function* () {
       const plugins = yield* PluginV2.Service
       const registry = yield* ToolRegistry.Service
@@ -286,13 +286,13 @@ describe("PluginV2", () => {
           execute: () => Effect.succeed({ ok: true }),
         })
       const plugin = EffectPlugin.define({
-        id: "grouped-tools",
+        id: "namespaced-tools",
         effect: (ctx) =>
           ctx.tool
             .transform((draft) => {
               draft.add("plain", tool("Plain"), { codemode: false })
-              draft.add("look/up", tool("Lookup"), { group: "context 7", codemode: false })
-              draft.add("search", tool("Search"), { group: "context 7" })
+              draft.add("look/up", tool("Lookup"), { namespace: "context 7", codemode: false })
+              draft.add("search", tool("Search"), { namespace: "context 7" })
             })
             .pipe(Effect.orDie),
       })
@@ -307,6 +307,41 @@ describe("PluginV2", () => {
     }),
   )
 
+  it.effect("accepts flat Effect draft declarations with namespace", () =>
+    Effect.gen(function* () {
+      const plugins = yield* PluginV2.Service
+      const registry = yield* ToolRegistry.Service
+      const plugin = EffectPlugin.define({
+        id: "flat-tools",
+        effect: (ctx) =>
+          ctx.tool
+            .transform((draft) => {
+              draft.add({
+                name: "send",
+                namespace: "slack",
+                description: "Send a Slack message",
+                input: Schema.Struct({ text: Schema.String }),
+                output: Schema.Struct({ sent: Schema.Boolean }),
+                execute: () => Effect.succeed({ sent: true }),
+              })
+              draft.add({
+                name: "edit",
+                codemode: false,
+                description: "Edit a file",
+                input: Schema.Struct({}),
+                output: Schema.Struct({ ok: Schema.Boolean }),
+                execute: () => Effect.succeed({ ok: true }),
+              })
+            })
+            .pipe(Effect.orDie),
+      })
+
+      yield* plugins.activate([versioned(plugin)])
+
+      expect((yield* registry.materialize()).definitions.map((tool) => tool.name)).toEqual(["edit", "execute"])
+    }),
+  )
+
   it.effect("fires before/after tool hooks with mutable events around settlement", () =>
     Effect.gen(function* () {
       const plugins = yield* PluginV2.Service
diff --git a/packages/core/test/plugin/promise.test.ts b/packages/core/test/plugin/promise.test.ts
index afe72f6b59f7..57d15fb5ed19 100644
--- a/packages/core/test/plugin/promise.test.ts
+++ b/packages/core/test/plugin/promise.test.ts
@@ -135,7 +135,7 @@ describe("fromPromise", () => {
           await ctx.tool.transform((tools) => {
             tools.add({
               name: "hello",
-              options: { codemode: false },
+              codemode: false,
               description: "Hello",
               input: Schema.Struct({ name: Schema.String }),
               output: Schema.String,
diff --git a/packages/docs/build/plugins.mdx b/packages/docs/build/plugins.mdx
index ad9cff8a3e9e..7ada606cd1ba 100644
--- a/packages/docs/build/plugins.mdx
+++ b/packages/docs/build/plugins.mdx
@@ -312,12 +312,13 @@ export default Plugin.define({
 })
 ```
 
-Unsupported characters in tool and group names are normalized to underscores.
+Unsupported characters in tool and namespace names are normalized to underscores.
 The resulting exposed key must begin with a letter and contain at most 64
-letters, digits, underscores, or hyphens. Set `options` on the declaration to
-configure registration with `{ group, codemode }`:
+letters, digits, underscores, or hyphens. Set registration fields on the
+declaration or options with `{ namespace, codemode }`:
 
-- `group` prefixes and groups the exposed tool name.
+- `namespace` prefixes the exposed tool name (and becomes the CodeMode path
+  segment).
 - `codemode` defaults to `true` and makes the tool available through the
   `execute` CodeMode tool. Set `codemode: false` to expose it directly to the
   provider.
diff --git a/packages/plugin/src/v2/effect/tool.ts b/packages/plugin/src/v2/effect/tool.ts
index ce53b78bd386..a86c8df6ef0b 100644
--- a/packages/plugin/src/v2/effect/tool.ts
+++ b/packages/plugin/src/v2/effect/tool.ts
@@ -123,6 +123,17 @@ export function make(config: Config<any, any, any> | DynamicConfig): AnyTool {
   return makeTyped(config)
 }
 
+/**
+ * Split a flat tool declaration into its registration name, opaque Tool value,
+ * and registration options. Narrowing on `jsonSchema` selects the matching
+ * constructor, so no cast is needed to build the Tool from the flat union.
+ */
+export function fromFlat(flat: FlatDefinition<any, any, any> | FlatDynamicDefinition) {
+  const { name, namespace, codemode, ...config } = flat
+  const tool = "jsonSchema" in config ? makeDynamic(config) : makeTyped(config)
+  return { name, tool, options: { namespace, codemode } satisfies RegisterOptions }
+}
+
 function makeTyped<
   Input extends SchemaType<any>,
   Output extends SchemaType<any>,
@@ -212,14 +223,14 @@ export const validateName = (name: string) =>
     ? Effect.void
     : Effect.fail(new RegistrationError({ name, message: `Invalid tool name: ${name}` }))
 
-export const registrationEntries = (tools: Readonly<Record<string, AnyTool>>, group?: string) =>
+export const registrationEntries = (tools: Readonly<Record<string, AnyTool>>, namespace?: string) =>
   Object.entries(tools).map(([name, tool]) => {
     const normalized = name.replace(/[^a-zA-Z0-9_-]/g, "_")
-    const parent = group?.replace(/[^a-zA-Z0-9_-]/g, "_")
+    const parent = namespace?.replace(/[^a-zA-Z0-9_-]/g, "_")
     return {
       key: parent === undefined ? normalized : `${parent}_${normalized}`,
       name: normalized,
-      group: parent,
+      namespace: parent,
       tool,
     }
   })
@@ -271,15 +282,68 @@ export interface ToolExecuteAfterEvent {
 }
 
 export interface RegisterOptions {
-  readonly group?: string
+  /** Dotted CodeMode path prefix, e.g. "slack.admin". */
+  readonly namespace?: string
   /** Defaults to true. False exposes the tool directly to the provider. */
   readonly codemode?: boolean
 }
 
+export type FlatDefinition<
+  Input extends SchemaType<any>,
+  Output extends SchemaType<any>,
+  Structured extends SchemaType<any> = Output,
+> = {
+  readonly name: string
+  readonly namespace?: string
+  readonly codemode?: boolean
+  readonly description: string
+  readonly input: Input
+  readonly output: Output
+  readonly structured?: Structured
+  readonly toStructuredOutput?: Config<Input, Output, Structured>["toStructuredOutput"]
+  readonly execute: Config<Input, Output, Structured>["execute"]
+  readonly toModelOutput?: Config<Input, Output, Structured>["toModelOutput"]
+}
+
+export type FlatDynamicDefinition = {
+  readonly name: string
+  readonly namespace?: string
+  readonly codemode?: boolean
+  readonly description: string
+  readonly jsonSchema: JsonSchema.JsonSchema
+  readonly outputSchema?: JsonSchema.JsonSchema
+  readonly execute: DynamicConfig["execute"]
+}
+
 export interface ToolDraft {
+  add<
+    Input extends SchemaType<any>,
+    Output extends SchemaType<any>,
+    Structured extends SchemaType<any> = Output,
+  >(tool: FlatDefinition<Input, Output, Structured>): void
+  add(tool: FlatDynamicDefinition): void
   add(name: string, tool: AnyTool, options?: RegisterOptions): void
 }
 
+export type Registration = {
+  readonly name: string
+  readonly tool: AnyTool
+  readonly options?: RegisterOptions
+}
+
+/** Run a draft callback and collect the tools it declared, in registration order. */
+export function fromDraft(callback: (draft: ToolDraft) => void) {
+  const registrations: Array<Registration> = []
+  const add = (
+    nameOrTool: string | FlatDefinition<any, any, any> | FlatDynamicDefinition,
+    tool?: AnyTool,
+    options?: RegisterOptions,
+  ) =>
+    registrations.push(typeof nameOrTool === "string" ? { name: nameOrTool, tool: tool!, options } : fromFlat(nameOrTool))
+  callback({ add })
+  return registrations
+}
+
 export interface ToolHooks {
   readonly "execute.before": ToolExecuteBeforeEvent
   readonly "execute.after": ToolExecuteAfterEvent
diff --git a/packages/plugin/src/v2/promise/tool.ts b/packages/plugin/src/v2/promise/tool.ts
index 77d936f5800f..62756719cc5c 100644
--- a/packages/plugin/src/v2/promise/tool.ts
+++ b/packages/plugin/src/v2/promise/tool.ts
@@ -16,7 +16,8 @@ export type Definition<
   Structured extends SchemaType<any> = Output,
 > = {
   readonly name: string
-  readonly options?: RegisterOptions
+  readonly namespace?: string
+  readonly codemode?: boolean
   readonly description: string
   readonly input: Input
   readonly output: Output
@@ -37,7 +38,8 @@ export type Definition<
 
 export type DynamicDefinition = {
   readonly name: string
-  readonly options?: RegisterOptions
+  readonly namespace?: string
+  readonly codemode?: boolean
   readonly description: string
   readonly jsonSchema: JsonSchema.JsonSchema
   readonly outputSchema?: JsonSchema.JsonSchema
@@ -67,12 +69,6 @@ export interface ToolExecuteAfterEvent {
   outputPaths?: ReadonlyArray<string>
 }
 
-export interface RegisterOptions {
-  readonly group?: string
-  /** Defaults to true. False exposes the tool directly to the provider. */
-  readonly codemode?: boolean
-}
-
 export interface ToolDraft {
   add<
     Input extends SchemaType<any>,