diff --git a/langchain-core/src/messages/ai.ts b/langchain-core/src/messages/ai.ts
index b1b4c5261378..001413dad45b 100644
--- a/langchain-core/src/messages/ai.ts
+++ b/langchain-core/src/messages/ai.ts
@@ -7,13 +7,10 @@ import {
   type MessageType,
   BaseMessageFields,
   _mergeLists,
-} from "./base.js";
-import {
-  InvalidToolCall,
   ToolCall,
   ToolCallChunk,
-  defaultToolCallParser,
-} from "./tool.js";
+} from "./base.js";
+import { InvalidToolCall, defaultToolCallParser } from "./tool.js";
 
 export type AIMessageFields = BaseMessageFields & {
   tool_calls?: ToolCall[];
diff --git a/langchain-core/src/messages/base.ts b/langchain-core/src/messages/base.ts
index 521f5b77935b..c5a60e81e56b 100644
--- a/langchain-core/src/messages/base.ts
+++ b/langchain-core/src/messages/base.ts
@@ -172,6 +172,23 @@ function stringifyWithDepthLimit(obj: any, depthLimit: number): string {
   return JSON.stringify(helper(obj, 0), null, 2);
 }
 
+/**
+ * A call to a tool.
+ * @property {string} name - The name of the tool to be called
+ * @property {Record<string, any>} args - The arguments to the tool call
+ * @property {string} [id] - If provided, an identifier associated with the tool call
+ */
+export type ToolCall = {
+  name: string;
+
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  args: Record<string, any>;
+
+  id?: string;
+
+  type?: "tool_call";
+};
+
 /**
  * Base class for all types of messages in a conversation. It includes
  * properties like `content`, `name`, and `additional_kwargs`. It also
@@ -219,6 +236,8 @@ export abstract class BaseMessage
    */
   id?: string;
 
+  tool_calls?: never[] | ToolCall[];
+
   /**
    * @deprecated Use .getType() instead or import the proper typeguard.
    * For example:
@@ -457,6 +476,76 @@ export function _mergeObj<T = any>(
   }
 }
 
+/**
+ * A chunk of a tool call (e.g., as part of a stream).
+ * When merging ToolCallChunks (e.g., via AIMessageChunk.__add__),
+ * all string attributes are concatenated. Chunks are only merged if their
+ * values of `index` are equal and not None.
+ *
+ * @example
+ * ```ts
+ * const leftChunks = [
+ *   {
+ *     name: "foo",
+ *     args: '{"a":',
+ *     index: 0
+ *   }
+ * ];
+ *
+ * const leftAIMessageChunk = new AIMessageChunk({
+ *   content: "",
+ *   tool_call_chunks: leftChunks
+ * });
+ *
+ * const rightChunks = [
+ *   {
+ *     name: undefined,
+ *     args: '1}',
+ *     index: 0
+ *   }
+ * ];
+ *
+ * const rightAIMessageChunk = new AIMessageChunk({
+ *   content: "",
+ *   tool_call_chunks: rightChunks
+ * });
+ *
+ * const result = leftAIMessageChunk.concat(rightAIMessageChunk);
+ * // result.tool_call_chunks is equal to:
+ * // [
+ * //   {
+ * //     name: "foo",
+ * //     args: '{"a":1}'
+ * //     index: 0
+ * //   }
+ * // ]
+ * ```
+ *
+ * @property {string} [name] - If provided, a substring of the name of the tool to be called
+ * @property {string} [args] - If provided, a JSON substring of the arguments to the tool call
+ * @property {string} [id] - If provided, a substring of an identifier for the tool call
+ * @property {number} [index] - If provided, the index of the tool call in a sequence
+ */
+export type ToolCallChunk = {
+  name?: string;
+
+  args?: string;
+
+  id?: string;
+
+  index?: number;
+
+  type?: "tool_call_chunk";
+};
+
+export type InvalidToolCall = {
+  name?: string;
+  args?: string;
+  id?: string;
+  error?: string;
+  type?: "invalid_tool_call";
+};
+
 /**
  * Represents a chunk of a message, which can be concatenated with other
  * message chunks. It includes a method `_merge_kwargs_dict()` for merging
@@ -465,6 +554,10 @@ export function _mergeObj<T = any>(
  * of `BaseMessageChunk` instances.
  */
 export abstract class BaseMessageChunk extends BaseMessage {
+  tool_call_chunks?: never[] | ToolCallChunk[];
+
+  invalid_tool_calls?: never[] | InvalidToolCall[];
+
   abstract concat(chunk: BaseMessageChunk): BaseMessageChunk;
 }
 
diff --git a/langchain-core/src/messages/chat.ts b/langchain-core/src/messages/chat.ts
index 376c05cceb84..a04081e75b13 100644
--- a/langchain-core/src/messages/chat.ts
+++ b/langchain-core/src/messages/chat.ts
@@ -18,6 +18,8 @@ export class ChatMessage
   extends BaseMessage
   implements ChatMessageFieldsWithRole
 {
+  declare tool_calls?: never[];
+
   static lc_name() {
     return "ChatMessage";
   }
@@ -62,6 +64,12 @@ export class ChatMessage
  * other chat message chunks.
  */
 export class ChatMessageChunk extends BaseMessageChunk {
+  declare tool_calls?: never[];
+
+  declare tool_call_chunks?: never[];
+
+  declare invalid_tool_calls?: never[];
+
   static lc_name() {
     return "ChatMessageChunk";
   }
diff --git a/langchain-core/src/messages/function.ts b/langchain-core/src/messages/function.ts
index 7e3455b8ca51..7cb4c832f496 100644
--- a/langchain-core/src/messages/function.ts
+++ b/langchain-core/src/messages/function.ts
@@ -15,6 +15,8 @@ export interface FunctionMessageFieldsWithName extends BaseMessageFields {
  * Represents a function message in a conversation.
  */
 export class FunctionMessage extends BaseMessage {
+  declare tool_calls?: never[];
+
   static lc_name() {
     return "FunctionMessage";
   }
@@ -49,6 +51,12 @@ export class FunctionMessage extends BaseMessage {
  * with other function message chunks.
  */
 export class FunctionMessageChunk extends BaseMessageChunk {
+  declare tool_calls?: never[];
+
+  declare tool_call_chunks?: never[];
+
+  declare invalid_tool_calls?: never[];
+
   static lc_name() {
     return "FunctionMessageChunk";
   }
diff --git a/langchain-core/src/messages/human.ts b/langchain-core/src/messages/human.ts
index 30b5354ee509..ba34c5b8f12a 100644
--- a/langchain-core/src/messages/human.ts
+++ b/langchain-core/src/messages/human.ts
@@ -10,6 +10,8 @@ import {
  * Represents a human message in a conversation.
  */
 export class HumanMessage extends BaseMessage {
+  declare tool_calls?: never[];
+
   static lc_name() {
     return "HumanMessage";
   }
@@ -24,6 +26,12 @@ export class HumanMessage extends BaseMessage {
  * other human message chunks.
  */
 export class HumanMessageChunk extends BaseMessageChunk {
+  declare tool_calls?: never[];
+
+  declare tool_call_chunks?: never[];
+
+  declare invalid_tool_calls?: never[];
+
   static lc_name() {
     return "HumanMessageChunk";
   }
diff --git a/langchain-core/src/messages/modifier.ts b/langchain-core/src/messages/modifier.ts
index aab91151a8fb..9457adffbf63 100644
--- a/langchain-core/src/messages/modifier.ts
+++ b/langchain-core/src/messages/modifier.ts
@@ -12,6 +12,8 @@ export interface RemoveMessageFields
  * Message responsible for deleting other messages.
  */
 export class RemoveMessage extends BaseMessage {
+  declare tool_calls?: never[];
+
   /**
    * The ID of the message to remove.
    */
diff --git a/langchain-core/src/messages/system.ts b/langchain-core/src/messages/system.ts
index ae91a240e83f..c258dff10a19 100644
--- a/langchain-core/src/messages/system.ts
+++ b/langchain-core/src/messages/system.ts
@@ -10,6 +10,8 @@ import {
  * Represents a system message in a conversation.
  */
 export class SystemMessage extends BaseMessage {
+  declare tool_calls?: never[];
+
   static lc_name() {
     return "SystemMessage";
   }
@@ -24,6 +26,12 @@ export class SystemMessage extends BaseMessage {
  * other system message chunks.
  */
 export class SystemMessageChunk extends BaseMessageChunk {
+  declare tool_calls?: never[];
+
+  declare tool_call_chunks?: never[];
+
+  declare invalid_tool_calls?: never[];
+
   static lc_name() {
     return "SystemMessageChunk";
   }
diff --git a/langchain-core/src/messages/tests/message_utils.test.ts b/langchain-core/src/messages/tests/message_utils.test.ts
index 222d9b42372a..9f137ba9a8b6 100644
--- a/langchain-core/src/messages/tests/message_utils.test.ts
+++ b/langchain-core/src/messages/tests/message_utils.test.ts
@@ -4,16 +4,22 @@ import {
   mergeMessageRuns,
   trimMessages,
 } from "../transformers.js";
-import { AIMessage } from "../ai.js";
-import { ChatMessage } from "../chat.js";
-import { HumanMessage } from "../human.js";
-import { SystemMessage } from "../system.js";
-import { BaseMessage } from "../base.js";
+import { AIMessage, isAIMessage, isAIMessageChunk } from "../ai.js";
+import { ChatMessage, isChatMessage, isChatMessageChunk } from "../chat.js";
+import { HumanMessage, isHumanMessage, isHumanMessageChunk } from "../human.js";
+import {
+  isSystemMessage,
+  isSystemMessageChunk,
+  SystemMessage,
+  SystemMessageChunk,
+} from "../system.js";
+import { BaseMessage, BaseMessageChunk } from "../base.js";
 import {
   getBufferString,
   mapChatMessagesToStoredMessages,
   mapStoredMessagesToChatMessages,
 } from "../utils.js";
+import { isToolMessage, isToolMessageChunk } from "../tool.js";
 
 describe("filterMessage", () => {
   const getMessages = () => [
@@ -520,3 +526,91 @@ describe("chat message conversions", () => {
     expect(convertedBackMessages).toEqual(originalMessages);
   });
 });
+
+it("Should narrow tool call typing when accessing a base message array", async () => {
+  const messages: BaseMessage[] = [new SystemMessage("test")];
+  if (messages[0].tool_calls?.[0] !== undefined) {
+    // Allow checking existence on BaseMessage with no errors
+    void messages[0].tool_calls[0].args;
+  }
+
+  const msg = messages[0];
+  if (isAIMessage(msg)) {
+    // Should allow access from AI messages
+    void msg.tool_calls?.[0].args;
+  }
+  if (isHumanMessage(msg)) {
+    // @ts-expect-error Typing should not allow access from human messages
+    void msg.tool_calls?.[0].args;
+  }
+  if (isSystemMessage(msg)) {
+    // @ts-expect-error Typing should not allow access from system messages
+    void msg.tool_calls?.[0].args;
+  }
+  if (isToolMessage(msg)) {
+    // @ts-expect-error Typing should not allow access from tool messages
+    void msg.tool_calls?.[0].args;
+  }
+  if (isChatMessage(msg)) {
+    // @ts-expect-error Typing should not allow access from chat messages
+    void msg.tool_calls?.[0].args;
+  }
+
+  const messageChunks: BaseMessageChunk[] = [new SystemMessageChunk("test")];
+  if (messageChunks[0].tool_calls?.[0] !== undefined) {
+    // Allow checking existence on BaseMessage with no errors
+    void messageChunks[0].tool_calls[0].args;
+  }
+
+  if (messageChunks[0].tool_call_chunks?.[0] !== undefined) {
+    // Allow checking existence on BaseMessage with no errors
+    void messageChunks[0].tool_call_chunks[0].args;
+  }
+
+  if (messageChunks[0].invalid_tool_calls?.[0] !== undefined) {
+    // Allow checking existence on BaseMessage with no errors
+    void messageChunks[0].invalid_tool_calls[0].args;
+  }
+
+  const msgChunk = messageChunks[0];
+  if (isAIMessageChunk(msgChunk)) {
+    // Typing should allow access from AI message chunks
+    void msgChunk.tool_calls?.[0].args;
+    // Typing should allow access from AI message chunks
+    void msgChunk.tool_call_chunks?.[0].args;
+    // Typing should allow access from AI message chunks
+    void msgChunk.invalid_tool_calls?.[0].args;
+  }
+  if (isHumanMessageChunk(msgChunk)) {
+    // @ts-expect-error Typing should not allow access from human message chunks
+    void msgChunk.tool_calls?.[0].args;
+    // @ts-expect-error Typing should not allow access from human message chunks
+    void msgChunk.tool_call_chunks?.[0].args;
+    // @ts-expect-error Typing should not allow access from human message chunks
+    void msgChunk.invalid_tool_calls?.[0].args;
+  }
+  if (isSystemMessageChunk(msgChunk)) {
+    // @ts-expect-error Typing should not allow access from system message chunks
+    void msgChunk.tool_calls?.[0].args;
+    // @ts-expect-error Typing should not allow access from system message chunks
+    void msgChunk.tool_call_chunks?.[0].args;
+    // @ts-expect-error Typing should not allow access from system message chunks
+    void msgChunk.invalid_tool_calls?.[0].args;
+  }
+  if (isToolMessageChunk(msgChunk)) {
+    // @ts-expect-error Typing should not allow access from tool message chunks
+    void msgChunk.tool_calls?.[0].args;
+    // @ts-expect-error Typing should not allow access from tool message chunks
+    void msgChunk.tool_call_chunks?.[0].args;
+    // @ts-expect-error Typing should not allow access from tool message chunks
+    void msgChunk.invalid_tool_calls?.[0].args;
+  }
+  if (isChatMessageChunk(msgChunk)) {
+    // @ts-expect-error Typing should not allow access from chat message chunks
+    void msgChunk.tool_calls?.[0].args;
+    // @ts-expect-error Typing should not allow access from chat message chunks
+    void msgChunk.tool_call_chunks?.[0].args;
+    // @ts-expect-error Typing should not allow access from chat message chunks
+    void msgChunk.invalid_tool_calls?.[0].args;
+  }
+});
diff --git a/langchain-core/src/messages/tool.ts b/langchain-core/src/messages/tool.ts
index 1b3f555a7349..22d9d266aaae 100644
--- a/langchain-core/src/messages/tool.ts
+++ b/langchain-core/src/messages/tool.ts
@@ -7,6 +7,9 @@ import {
   type MessageType,
   _mergeObj,
   _mergeStatus,
+  ToolCall,
+  ToolCallChunk,
+  InvalidToolCall,
 } from "./base.js";
 
 export interface ToolMessageFieldsWithToolCallId extends BaseMessageFields {
@@ -51,6 +54,8 @@ export function isDirectToolOutput(x: unknown): x is DirectToolOutput {
  * Represents a tool message in a conversation.
  */
 export class ToolMessage extends BaseMessage implements DirectToolOutput {
+  declare tool_calls?: never[];
+
   static lc_name() {
     return "ToolMessage";
   }
@@ -125,6 +130,12 @@ export class ToolMessage extends BaseMessage implements DirectToolOutput {
  * with other tool message chunks.
  */
 export class ToolMessageChunk extends BaseMessageChunk {
+  declare tool_calls?: never[];
+
+  declare tool_call_chunks?: never[];
+
+  declare invalid_tool_calls?: never[];
+
   tool_call_id: string;
 
   /**
@@ -185,92 +196,7 @@ export class ToolMessageChunk extends BaseMessageChunk {
   }
 }
 
-/**
- * A call to a tool.
- * @property {string} name - The name of the tool to be called
- * @property {Record<string, any>} args - The arguments to the tool call
- * @property {string} [id] - If provided, an identifier associated with the tool call
- */
-export type ToolCall = {
-  name: string;
-
-  // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  args: Record<string, any>;
-
-  id?: string;
-
-  type?: "tool_call";
-};
-
-/**
- * A chunk of a tool call (e.g., as part of a stream).
- * When merging ToolCallChunks (e.g., via AIMessageChunk.__add__),
- * all string attributes are concatenated. Chunks are only merged if their
- * values of `index` are equal and not None.
- *
- * @example
- * ```ts
- * const leftChunks = [
- *   {
- *     name: "foo",
- *     args: '{"a":',
- *     index: 0
- *   }
- * ];
- *
- * const leftAIMessageChunk = new AIMessageChunk({
- *   content: "",
- *   tool_call_chunks: leftChunks
- * });
- *
- * const rightChunks = [
- *   {
- *     name: undefined,
- *     args: '1}',
- *     index: 0
- *   }
- * ];
- *
- * const rightAIMessageChunk = new AIMessageChunk({
- *   content: "",
- *   tool_call_chunks: rightChunks
- * });
- *
- * const result = leftAIMessageChunk.concat(rightAIMessageChunk);
- * // result.tool_call_chunks is equal to:
- * // [
- * //   {
- * //     name: "foo",
- * //     args: '{"a":1}'
- * //     index: 0
- * //   }
- * // ]
- * ```
- *
- * @property {string} [name] - If provided, a substring of the name of the tool to be called
- * @property {string} [args] - If provided, a JSON substring of the arguments to the tool call
- * @property {string} [id] - If provided, a substring of an identifier for the tool call
- * @property {number} [index] - If provided, the index of the tool call in a sequence
- */
-export type ToolCallChunk = {
-  name?: string;
-
-  args?: string;
-
-  id?: string;
-
-  index?: number;
-
-  type?: "tool_call_chunk";
-};
-
-export type InvalidToolCall = {
-  name?: string;
-  args?: string;
-  id?: string;
-  error?: string;
-  type?: "invalid_tool_call";
-};
+export type { ToolCall, ToolCallChunk, InvalidToolCall };
 
 export function defaultToolCallParser(
   // eslint-disable-next-line @typescript-eslint/no-explicit-any