diff --git a/denops/@dpp-exts/local.ts b/denops/@dpp-exts/local.ts
index 99c634a..a0ab50e 100644
--- a/denops/@dpp-exts/local.ts
+++ b/denops/@dpp-exts/local.ts
@@ -1,10 +1,5 @@
-import {
-  Actions,
-  BaseExt,
-} from "../dpp/types.ts";
-import {
-  Denops,
-} from "../dpp/deps.ts";
+import { Actions, BaseExt } from "../dpp/types.ts";
+import { Denops } from "../dpp/deps.ts";
 
 type Params = Record<string, never>;
 
@@ -16,7 +11,7 @@ export class Ext extends BaseExt<Params> {
         console.log("hello");
       },
     },
-  }
+  };
 
   override params(): Params {
     return {};
diff --git a/denops/dpp/base/config.ts b/denops/dpp/base/config.ts
index 7650520..fc0f0e1 100644
--- a/denops/dpp/base/config.ts
+++ b/denops/dpp/base/config.ts
@@ -1,8 +1,12 @@
+import { ContextBuilder } from "../context.ts";
 import { Denops } from "../deps.ts";
+import { Dpp } from "../types.ts";
 
 export type ConfigArguments = {
   denops: Denops;
   basePath: string;
+  contextBuilder: ContextBuilder;
+  dpp: Dpp;
 };
 
 export abstract class BaseConfig {
diff --git a/denops/dpp/base/ext.ts b/denops/dpp/base/ext.ts
index cf38dce..3aa6bef 100644
--- a/denops/dpp/base/ext.ts
+++ b/denops/dpp/base/ext.ts
@@ -1,7 +1,14 @@
-import { Actions } from "../types.ts";
+import { Denops } from "../deps.ts";
+import { Actions, ExtOptions } from "../types.ts";
 
 export type BaseExtParams = Record<string, unknown>;
 
+export type OnInitArguments<Params extends BaseExtParams> = {
+  denops: Denops;
+  extOptions: ExtOptions;
+  extParams: Params;
+};
+
 export abstract class BaseExt<Params extends BaseExtParams> {
   apiVersion = 1;
 
@@ -9,7 +16,13 @@ export abstract class BaseExt<Params extends BaseExtParams> {
   path = "";
   isInitialized = false;
 
+  onInit(_args: OnInitArguments<Params>): void | Promise<void> {}
+
   abstract params(): Params;
 
   actions: Actions<Params> = {};
 }
+
+export function defaultExtOptions(): ExtOptions {
+  return {};
+}
diff --git a/denops/dpp/dpp.ts b/denops/dpp/dpp.ts
index 10c185d..3630400 100644
--- a/denops/dpp/dpp.ts
+++ b/denops/dpp/dpp.ts
@@ -1,14 +1,147 @@
-import { ActionName, ExtName } from "./types.ts";
+import { Denops } from "./deps.ts";
+import {
+  ActionName,
+  BaseExt,
+  BaseExtParams,
+  Context,
+  DppOptions,
+  ExtName,
+  ExtOptions,
+} from "./types.ts";
+import {
+  defaultContext,
+  defaultDppOptions,
+  defaultDummy,
+  foldMerge,
+  mergeExtOptions,
+  mergeExtParams,
+} from "./context.ts";
 import { Loader } from "./loader.ts";
+import { defaultExtOptions } from "./base/ext.ts";
 import { errorException } from "./utils.ts";
 
 export class Dpp {
   private loader: Loader;
+  private context: Context = defaultContext();
+  private options: DppOptions = defaultDppOptions();
 
   constructor(loader: Loader) {
     this.loader = loader;
   }
 
-  async extAction(extName: ExtName, actionName: ActionName, params: unknown) {
+  async extAction(
+    denops: Denops,
+    extName: ExtName,
+    actionName: ActionName,
+    actionParams: unknown = {},
+  ) {
+    const [ext, extOptions, extParams] = await this.getExt(denops, extName);
+    if (!ext) {
+      return;
+    }
+
+    const action = ext.actions[actionName];
+    if (!action) {
+      await denops.call(
+        "ddu#util#print_error",
+        `Not found UI action: ${actionName}`,
+      );
+      return;
+    }
+
+    const ret = await action.callback({
+      denops,
+      context: this.context,
+      options: this.options,
+      extOptions,
+      extParams,
+      actionParams,
+    });
+
+    return ret;
+  }
+
+  private async getExt(
+    denops: Denops,
+    extName: ExtName,
+  ): Promise<
+    [
+      BaseExt<BaseExtParams> | undefined,
+      ExtOptions,
+      BaseExtParams,
+    ]
+  > {
+    if (!this.loader.getExt(extName)) {
+      await this.loader.autoload(denops, "ext", extName);
+    }
+
+    const ext = this.loader.getExt(extName);
+    if (!ext) {
+      if (extName.length !== 0) {
+        await denops.call(
+          "dpp#util#print_error",
+          `Not found ext: "${extName}"`,
+        );
+      }
+      return [
+        undefined,
+        defaultExtOptions(),
+        defaultDummy(),
+      ];
+    }
+
+    const [extOptions, extParams] = extArgs(this.options, ext);
+    await checkExtOnInit(ext, denops, extOptions, extParams);
+
+    return [ext, extOptions, extParams];
   }
 }
+
+async function checkExtOnInit(
+  ext: BaseExt<BaseExtParams>,
+  denops: Denops,
+  extOptions: ExtOptions,
+  extParams: BaseExtParams,
+) {
+  if (ext.isInitialized) {
+    return;
+  }
+
+  try {
+    await ext.onInit({
+      denops,
+      extOptions,
+      extParams,
+    });
+
+    ext.isInitialized = true;
+  } catch (e: unknown) {
+    await errorException(
+      denops,
+      e,
+      `ext: ${ext.name} "onInit()" failed`,
+    );
+  }
+}
+
+function extArgs<
+  Params extends BaseExtParams,
+>(
+  options: DppOptions,
+  ext: BaseExt<Params>,
+): [ExtOptions, BaseExtParams] {
+  const o = foldMerge(
+    mergeExtOptions,
+    defaultExtOptions,
+    [
+      options.extOptions["_"],
+      options.extOptions[ext.name],
+    ],
+  );
+  const p = foldMerge(mergeExtParams, defaultDummy, [
+    ext.params(),
+    options.extParams["_"],
+    options.extParams[ext.name],
+  ]);
+  return [o, p];
+}
diff --git a/denops/dpp/loader.ts b/denops/dpp/loader.ts
index 01ef264..85b88a2 100644
--- a/denops/dpp/loader.ts
+++ b/denops/dpp/loader.ts
@@ -16,7 +16,7 @@ type Mod = {
 };
 
 export class Loader {
-  private extensions: Record<string, Extension> = {};
+  private extension: Extension = new Extension();
   private mods: Record<DppExtType, Record<string, Mod>> = {
     ext: {},
     protocol: {},
@@ -48,32 +48,21 @@ export class Loader {
     });
   }
 
-  getExt(index: string, name: ExtName): BaseExt<BaseExtParams> | null {
+  getExt(name: ExtName): BaseExt<BaseExtParams> | null {
     const mod = this.mods.ext[name];
     if (!mod) {
       return null;
     }
 
-    return this.getExtension(index).getExt(mod, name);
+    return this.extension.getExt(mod, name);
   }
-  getProtocol(
-    index: string,
-    name: ProtocolName,
-  ): BaseProtocol<BaseProtocolParams> | null {
+  getProtocol(name: ProtocolName): BaseProtocol<BaseProtocolParams> | null {
     const mod = this.mods.protocol[name];
     if (!mod) {
       return null;
     }
 
-    return this.getExtension(index).getProtocol(mod, name);
-  }
-
-  private getExtension(index: string): Extension {
-    if (!this.extensions[index]) {
-      this.extensions[index] = new Extension();
-    }
-
-    return this.extensions[index];
+    return this.extension.getProtocol(mod, name);
   }
 
   private async register(type: DppExtType, path: string) {