Fix: keep winston out of the published browser build by splitting the logger by platform

core/src/index.ts

@@ -4,6 +4,16 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import {installNodeLogger} from './utils/logger_node.js';
+
+// The Node entry point installs the winston-backed logger. `utils/logger.ts`
+// itself must stay free of Node-only imports so that the browser entry point
+// can reach it; see https://github.com/google/adk-js/issues/611.
+// This call runs after the modules re-exported below are evaluated, so a module
+// must log through the `logger` facade instead of holding the result of
+// `getLogger()`.
+installNodeLogger();
+
 export {AGENT_CARD_PATH, RemoteA2AAgent} from './a2a/a2a_remote_agent.js';
 export type {
   A2AStreamEventData,

core/src/tools/load_artifacts_tool.ts

@@ -8,15 +8,13 @@ import {FunctionDeclaration, Part, Type} from '@google/genai';
 
 import {Context} from '../agents/context.js';
 import {appendInstructions, LlmRequest} from '../models/llm_request.js';
-import {getLogger} from '../utils/logger.js';
+import {logger} from '../utils/logger.js';
 import {
   BaseTool,
   RunAsyncToolRequest,
   ToolProcessLlmRequest,
 } from './base_tool.js';
 
-const logger = getLogger();
-
 const GEMINI_SUPPORTED_INLINE_MIME_PREFIXES = ['image/', 'audio/', 'video/'];
 const GEMINI_SUPPORTED_INLINE_MIME_TYPES = new Set(['application/pdf']);
 const TEXT_LIKE_MIME_TYPES = new Set([

core/src/tools/vertex_ai_search_tool.ts

@@ -6,16 +6,14 @@
 
 import {GenerateContentConfig, Tool} from '@google/genai';
 import {ReadonlyContext} from '../agents/readonly_context.js';
-import {getLogger} from '../utils/logger.js';
+import {logger} from '../utils/logger.js';
 import {
   isGemini1Model,
   isGeminiModel,
   isGeminiModelIdCheckDisabled,
 } from '../utils/model_name.js';
 import {BaseTool, ToolProcessLlmRequest} from './base_tool.js';
 
-const logger = getLogger();
-
 export interface VertexAISearchDataStoreSpec {
   dataStore?: string;
 }

core/src/utils/logger.ts

@@ -3,7 +3,6 @@
  * Copyright 2025 Google LLC
  * SPDX-License-Identifier: Apache-2.0
  */
-import * as winston from 'winston';
 
 /** Log levels for the logger. */
 export enum LogLevel {
@@ -30,35 +29,24 @@ export interface Logger {
   setLogLevel(level: LogLevel): void;
 }
 
+/** The `console` method each level is written with. */
+const CONSOLE_METHOD = {
+  [LogLevel.DEBUG]: 'debug',
+  [LogLevel.INFO]: 'info',
+  [LogLevel.WARN]: 'warn',
+  [LogLevel.ERROR]: 'error',
+} as const;
+
+/**
+ * The default logger. Writes through `console` so that it works unchanged in
+ * Node and in the browser. This module is reachable from the browser entry
+ * point, so it must not name a Node-only package; the Node entry point
+ * installs the winston-backed logger instead.
+ * See https://github.com/google/adk-js/issues/611.
+ */
 class SimpleLogger implements Logger {
-  private readonly logger: winston.Logger;
   private logLevel: LogLevel = LogLevel.INFO;
 
-  constructor() {
-    this.logger = winston.createLogger({
-      levels: {
-        'debug': LogLevel.DEBUG,
-        'info': LogLevel.INFO,
-        'warn': LogLevel.WARN,
-        'error': LogLevel.ERROR,
-      },
-      level: 'error',
-      format: winston.format.combine(
-        winston.format.label({label: 'ADK'}),
-        winston.format((info) => {
-          info.level = info.level.toUpperCase();
-          return info;
-        })(),
-        winston.format.colorize(),
-        winston.format.timestamp(),
-        winston.format.printf((info) => {
-          return `${info.level}: [${info.label}] ${info.timestamp} ${info.message}`;
-        }),
-      ),
-      transports: [new winston.transports.Console()],
-    });
-  }
-
   setLogLevel(level: LogLevel): void {
     this.logLevel = level;
   }
@@ -68,39 +56,26 @@ class SimpleLogger implements Logger {
       return;
     }
 
-    this.logger.log(level.toString(), messages.join(' '));
+    const timestamp = new Date().toISOString();
+    const line = `${LogLevel[level]}: [ADK] ${timestamp} ${messages.join(' ')}`;
+
+    console[CONSOLE_METHOD[level]](line);
   }
 
   debug(...messages: unknown[]): void {
-    if (this.logLevel > LogLevel.DEBUG) {
-      return;
-    }
-
-    this.logger.debug(messages.join(' '));
+    this.log(LogLevel.DEBUG, ...messages);
   }
 
   info(...messages: unknown[]): void {
-    if (this.logLevel > LogLevel.INFO) {
-      return;
-    }
-
-    this.logger.info(messages.join(' '));
+    this.log(LogLevel.INFO, ...messages);
   }
 
   warn(...messages: unknown[]): void {
-    if (this.logLevel > LogLevel.WARN) {
-      return;
-    }
-
-    this.logger.warn(messages.join(' '));
+    this.log(LogLevel.WARN, ...messages);
   }
 
   error(...messages: unknown[]): void {
-    if (this.logLevel > LogLevel.ERROR) {
-      return;
-    }
-
-    this.logger.error(messages.join(' '));
+    this.log(LogLevel.ERROR, ...messages);
   }
 }
 
@@ -133,7 +108,8 @@ export function getLogger(): Logger {
 }
 
 /**
- * Resets the logger to the default SimpleLogger.
+ * Resets the logger to the built-in console logger. On Node this replaces the
+ * winston-backed logger that the Node entry point installs.
  */
 export function resetLogger(): void {
   currentLogger = new SimpleLogger();

core/src/utils/logger_node.ts

@@ -0,0 +1,98 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * The Node-only logger implementation.
+ *
+ * This module is the only place under `core/src` that may name `winston`.
+ * `winston` needs Node built-ins, so no browser bundler can resolve it: this
+ * module must never become reachable from `core/src/index_web.ts`. The Node
+ * entry point (`core/src/index.ts`) wires it in through `setLogger`.
+ * See https://github.com/google/adk-js/issues/611.
+ */
+
+import * as winston from 'winston';
+import {Logger, LogLevel, setLogger} from './logger.js';
+
+/** The default logger on Node. Writes through winston. */
+export class WinstonLogger implements Logger {
+  private readonly logger: winston.Logger;
+  private logLevel: LogLevel = LogLevel.INFO;
+
+  constructor() {
+    this.logger = winston.createLogger({
+      levels: {
+        'debug': LogLevel.DEBUG,
+        'info': LogLevel.INFO,
+        'warn': LogLevel.WARN,
+        'error': LogLevel.ERROR,
+      },
+      level: 'error',
+      format: winston.format.combine(
+        winston.format.label({label: 'ADK'}),
+        winston.format((info) => {
+          info.level = info.level.toUpperCase();
+          return info;
+        })(),
+        winston.format.colorize(),
+        winston.format.timestamp(),
+        winston.format.printf((info) => {
+          return `${info.level}: [${info.label}] ${info.timestamp} ${info.message}`;
+        }),
+      ),
+      transports: [new winston.transports.Console()],
+    });
+  }
+
+  setLogLevel(level: LogLevel): void {
+    this.logLevel = level;
+  }
+
+  log(level: LogLevel, ...messages: unknown[]): void {
+    if (this.logLevel > level) {
+      return;
+    }
+
+    this.logger.log(level.toString(), messages.join(' '));
+  }
+
+  debug(...messages: unknown[]): void {
+    if (this.logLevel > LogLevel.DEBUG) {
+      return;
+    }
+
+    this.logger.debug(messages.join(' '));
+  }
+
+  info(...messages: unknown[]): void {
+    if (this.logLevel > LogLevel.INFO) {
+      return;
+    }
+
+    this.logger.info(messages.join(' '));
+  }
+
+  warn(...messages: unknown[]): void {
+    if (this.logLevel > LogLevel.WARN) {
+      return;
+    }
+
+    this.logger.warn(messages.join(' '));
+  }
+
+  error(...messages: unknown[]): void {
+    if (this.logLevel > LogLevel.ERROR) {
+      return;
+    }
+
+    this.logger.error(messages.join(' '));
+  }
+}
+
+/** Makes the winston-backed logger the current ADK logger. */
+export function installNodeLogger(): void {
+  setLogger(new WinstonLogger());
+}