diff --git a/packages/core/src/core/coreToolScheduler.ts b/packages/core/src/core/coreToolScheduler.ts
index fdf67dba8e..e6d4c62d9f 100644
--- a/packages/core/src/core/coreToolScheduler.ts
+++ b/packages/core/src/core/coreToolScheduler.ts
@@ -50,8 +50,7 @@ import { ToolExecutor } from '../scheduler/tool-executor.js';
 import { DiscoveredMCPTool } from '../tools/mcp-tool.js';
 import { getPolicyDenialError } from '../scheduler/policy.js';
 import { GeminiCliOperation } from '../telemetry/constants.js';
-import { extractMcpContext } from './coreToolHookTriggers.js';
-import { BeforeToolHookOutput } from '../hooks/types.js';
+import { evaluateBeforeToolHook } from '../scheduler/hook-utils.js';
 
 export type {
   ToolCall,
@@ -639,85 +638,48 @@ export class CoreToolScheduler {
         }
 
         // 1. Hook Check (BeforeTool)
-        let hookDecision: 'ask' | 'block' | undefined;
-        let hookSystemMessage: string | undefined;
+        const hookResult = await evaluateBeforeToolHook(
+          this.config,
+          toolCall.tool,
+          reqInfo,
+          invocation,
+        );
 
-        const hookSystem = this.config.getHookSystem();
-        if (hookSystem) {
-          // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
-          const toolInput = (invocation.params || {}) as Record<
-            string,
-            unknown
-          >;
-          const mcpContext = extractMcpContext(invocation, this.config);
-
-          const beforeOutput = await hookSystem.fireBeforeToolEvent(
-            toolCall.request.name,
-            toolInput,
-            mcpContext,
-            toolCall.request.originalRequestName,
+        if (hookResult.status === 'error') {
+          this.setStatusInternal(
+            reqInfo.callId,
+            CoreToolCallStatus.Error,
+            signal,
+            createErrorResponse(
+              reqInfo,
+              hookResult.error,
+              hookResult.errorType,
+            ),
           );
+          await this.checkAndNotifyCompletion(signal);
+          return;
+        }
 
-          if (beforeOutput) {
-            // Check if hook requested to stop entire agent execution
-            if (beforeOutput.shouldStopExecution()) {
-              const reason = beforeOutput.getEffectiveReason();
-              this.setStatusInternal(
-                reqInfo.callId,
-                CoreToolCallStatus.Error,
-                signal,
-                createErrorResponse(
-                  reqInfo,
-                  new Error(`Agent execution stopped by hook: ${reason}`),
-                  ToolErrorType.STOP_EXECUTION,
-                ),
-              );
-              await this.checkAndNotifyCompletion(signal);
-              return;
-            }
+        const { hookDecision, hookSystemMessage, modifiedArgs, newInvocation } =
+          hookResult;
 
-            // Check if hook blocked the tool execution
-            const blockingError = beforeOutput.getBlockingError();
-            if (blockingError?.blocked) {
-              this.setStatusInternal(
-                reqInfo.callId,
-                CoreToolCallStatus.Error,
-                signal,
-                createErrorResponse(
-                  reqInfo,
-                  new Error(`Tool execution blocked: ${blockingError.reason}`),
-                  ToolErrorType.POLICY_VIOLATION,
-                ),
-              );
-              await this.checkAndNotifyCompletion(signal);
-              return;
-            }
+        if (hookDecision === 'ask') {
+          // Mark the request so UI knows not to auto-approve it
+          toolCall.request.forcedAsk = true;
+        }
 
-            if (beforeOutput.isAskDecision()) {
-              hookDecision = 'ask';
-              hookSystemMessage = beforeOutput.systemMessage;
-              // Mark the request so UI knows not to auto-approve it
-              toolCall.request.forcedAsk = true;
-            }
+        if (modifiedArgs && newInvocation) {
+          this.setArgsInternal(reqInfo.callId, modifiedArgs);
 
-            // Check if hook requested to update tool input
-            if (beforeOutput instanceof BeforeToolHookOutput) {
-              const modifiedInput = beforeOutput.getModifiedToolInput();
-              if (modifiedInput) {
-                this.setArgsInternal(reqInfo.callId, modifiedInput);
-
-                // IMPORTANT: toolCall and invocation must be updated because setArgsInternal created a new one
-                const updatedCall = this.toolCalls.find(
-                  (c) => c.request.callId === reqInfo.callId,
-                );
-                if (updatedCall) {
-                  toolCall = updatedCall;
-                  toolCall.request.inputModifiedByHook = true;
-                  if ('invocation' in updatedCall) {
-                    invocation = updatedCall.invocation;
-                  }
-                }
-              }
+          // IMPORTANT: toolCall and invocation must be updated because setArgsInternal created a new one
+          const updatedCall = this.toolCalls.find(
+            (c) => c.request.callId === reqInfo.callId,
+          );
+          if (updatedCall) {
+            toolCall = updatedCall;
+            toolCall.request.inputModifiedByHook = true;
+            if ('invocation' in updatedCall) {
+              invocation = updatedCall.invocation;
             }
           }
         }
diff --git a/packages/core/src/scheduler/hook-utils.ts b/packages/core/src/scheduler/hook-utils.ts
new file mode 100644
index 0000000000..78d5aeaa53
--- /dev/null
+++ b/packages/core/src/scheduler/hook-utils.ts
@@ -0,0 +1,109 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type { Config } from '../config/config.js';
+import type { AnyDeclarativeTool, AnyToolInvocation } from '../tools/tools.js';
+import type { ToolCallRequestInfo } from './types.js';
+import { extractMcpContext } from '../core/coreToolHookTriggers.js';
+import { BeforeToolHookOutput } from '../hooks/types.js';
+import { ToolErrorType } from '../tools/tool-error.js';
+
+export type HookEvaluationResult =
+  | {
+      status: 'continue';
+      hookDecision?: 'ask' | 'block';
+      hookSystemMessage?: string;
+      modifiedArgs?: Record<string, unknown>;
+      newInvocation?: AnyToolInvocation;
+    }
+  | {
+      status: 'error';
+      error: Error;
+      errorType: ToolErrorType;
+    };
+
+export async function evaluateBeforeToolHook(
+  config: Config,
+  tool: AnyDeclarativeTool,
+  request: ToolCallRequestInfo,
+  invocation: AnyToolInvocation,
+): Promise<HookEvaluationResult> {
+  const hookSystem = config.getHookSystem();
+  if (!hookSystem) {
+    return { status: 'continue' };
+  }
+
+  const params = invocation.params || {};
+  const toolInput: Record<string, unknown> = { ...params };
+  const mcpContext = extractMcpContext(invocation, config);
+
+  const beforeOutput = await hookSystem.fireBeforeToolEvent(
+    request.name,
+    toolInput,
+    mcpContext,
+    request.originalRequestName,
+  );
+
+  if (!beforeOutput) {
+    return { status: 'continue' };
+  }
+
+  if (beforeOutput.shouldStopExecution()) {
+    return {
+      status: 'error',
+      error: new Error(
+        `Agent execution stopped by hook: ${beforeOutput.getEffectiveReason()}`,
+      ),
+      errorType: ToolErrorType.STOP_EXECUTION,
+    };
+  }
+
+  const blockingError = beforeOutput.getBlockingError();
+  if (blockingError?.blocked) {
+    return {
+      status: 'error',
+      error: new Error(`Tool execution blocked: ${blockingError.reason}`),
+      errorType: ToolErrorType.POLICY_VIOLATION,
+    };
+  }
+
+  let hookDecision: 'ask' | 'block' | undefined;
+  let hookSystemMessage: string | undefined;
+
+  if (beforeOutput.isAskDecision()) {
+    hookDecision = 'ask';
+    hookSystemMessage = beforeOutput.systemMessage;
+  }
+
+  let modifiedArgs: Record<string, unknown> | undefined;
+  let newInvocation: AnyToolInvocation | undefined;
+
+  if (beforeOutput instanceof BeforeToolHookOutput) {
+    const modifiedInput = beforeOutput.getModifiedToolInput();
+    if (modifiedInput) {
+      modifiedArgs = modifiedInput;
+      try {
+        newInvocation = tool.build(modifiedInput);
+      } catch (error) {
+        return {
+          status: 'error',
+          error: new Error(
+            `Tool parameter modification by hook failed validation: ${error instanceof Error ? error.message : String(error)}`,
+          ),
+          errorType: ToolErrorType.INVALID_TOOL_PARAMS,
+        };
+      }
+    }
+  }
+
+  return {
+    status: 'continue',
+    hookDecision,
+    hookSystemMessage,
+    modifiedArgs,
+    newInvocation,
+  };
+}
diff --git a/packages/core/src/scheduler/scheduler.ts b/packages/core/src/scheduler/scheduler.ts
index 8b841ee69e..9aa1eb376a 100644
--- a/packages/core/src/scheduler/scheduler.ts
+++ b/packages/core/src/scheduler/scheduler.ts
@@ -25,8 +25,8 @@ import {
   type ScheduledToolCall,
 } from './types.js';
 import { ToolErrorType } from '../tools/tool-error.js';
-import { extractMcpContext } from '../core/coreToolHookTriggers.js';
-import { BeforeToolHookOutput } from '../hooks/types.js';
+import { evaluateBeforeToolHook } from './hook-utils.js';
+
 import { PolicyDecision, type ApprovalMode } from '../policy/types.js';
 import {
   ToolConfirmationOutcome,
@@ -564,85 +564,37 @@ export class Scheduler {
   ): Promise<void> {
     const callId = toolCall.request.callId;
 
-    let hookDecision: 'ask' | 'block' | undefined;
-    let hookSystemMessage: string | undefined;
+    const hookResult = await evaluateBeforeToolHook(
+      this.config,
+      toolCall.tool,
+      toolCall.request,
+      toolCall.invocation,
+    );
 
-    const hookSystem = this.config.getHookSystem();
-    if (hookSystem) {
-      // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
-      const toolInput = (toolCall.invocation.params || {}) as Record<
-        string,
-        unknown
-      >;
-      const mcpContext = extractMcpContext(toolCall.invocation, this.config);
-
-      const beforeOutput = await hookSystem.fireBeforeToolEvent(
-        toolCall.request.name,
-        toolInput,
-        mcpContext,
-        toolCall.request.originalRequestName,
+    if (hookResult.status === 'error') {
+      this.state.updateStatus(
+        callId,
+        CoreToolCallStatus.Error,
+        createErrorResponse(
+          toolCall.request,
+          hookResult.error,
+          hookResult.errorType,
+        ),
       );
+      return;
+    }
 
-      if (beforeOutput) {
-        if (beforeOutput.shouldStopExecution()) {
-          this.state.updateStatus(
-            callId,
-            CoreToolCallStatus.Error,
-            createErrorResponse(
-              toolCall.request,
-              new Error(
-                `Agent execution stopped by hook: ${beforeOutput.getEffectiveReason()}`,
-              ),
-              ToolErrorType.STOP_EXECUTION,
-            ),
-          );
-          return;
-        }
+    const { hookDecision, hookSystemMessage, modifiedArgs, newInvocation } =
+      hookResult;
 
-        const blockingError = beforeOutput.getBlockingError();
-        if (blockingError?.blocked) {
-          this.state.updateStatus(
-            callId,
-            CoreToolCallStatus.Error,
-            createErrorResponse(
-              toolCall.request,
-              new Error(`Tool execution blocked: ${blockingError.reason}`),
-              ToolErrorType.POLICY_VIOLATION,
-            ),
-          );
-          return;
-        }
+    if (hookDecision === 'ask') {
+      toolCall.request.forcedAsk = true;
+    }
 
-        if (beforeOutput.isAskDecision()) {
-          hookDecision = 'ask';
-          hookSystemMessage = beforeOutput.systemMessage;
-          toolCall.request.forcedAsk = true;
-        }
-
-        if (beforeOutput instanceof BeforeToolHookOutput) {
-          const modifiedInput = beforeOutput.getModifiedToolInput();
-          if (modifiedInput) {
-            toolCall.request.args = modifiedInput;
-            toolCall.request.inputModifiedByHook = true;
-            try {
-              toolCall.invocation = toolCall.tool.build(modifiedInput);
-            } catch (error) {
-              this.state.updateStatus(
-                callId,
-                CoreToolCallStatus.Error,
-                createErrorResponse(
-                  toolCall.request,
-                  new Error(
-                    `Tool parameter modification by hook failed validation: ${error instanceof Error ? error.message : String(error)}`,
-                  ),
-                  ToolErrorType.INVALID_TOOL_PARAMS,
-                ),
-              );
-              return;
-            }
-          }
-        }
-      }
+    if (modifiedArgs && newInvocation) {
+      toolCall.request.args = modifiedArgs;
+      toolCall.request.inputModifiedByHook = true;
+      toolCall.invocation = newInvocation;
     }
 
     // Policy & Security
diff --git a/packages/core/src/tools/edit.ts b/packages/core/src/tools/edit.ts
index ae4b592f39..588f2b30fc 100644
--- a/packages/core/src/tools/edit.ts
+++ b/packages/core/src/tools/edit.ts
@@ -712,13 +712,13 @@ class EditToolInvocation
    * It needs to calculate the diff to show the user.
    */
   protected override async getConfirmationDetails(
-    _abortSignal: AbortSignal,
+    abortSignal: AbortSignal,
   ): Promise<ToolCallConfirmationDetails | false> {
     let editData: CalculatedEdit;
     try {
-      editData = await this.calculateEdit(this.params, _abortSignal);
+      editData = await this.calculateEdit(this.params, abortSignal);
     } catch (error) {
-      if (_abortSignal.aborted) {
+      if (abortSignal.aborted) {
         throw error;
       }
       const errorMsg = error instanceof Error ? error.message : String(error);
diff --git a/packages/core/src/tools/write-file.ts b/packages/core/src/tools/write-file.ts
index dc69c96f5e..0bb868eff8 100644
--- a/packages/core/src/tools/write-file.ts
+++ b/packages/core/src/tools/write-file.ts
@@ -181,13 +181,13 @@ class WriteFileToolInvocation extends BaseToolInvocation<
   }
 
   protected override async getConfirmationDetails(
-    _abortSignal: AbortSignal,
+    abortSignal: AbortSignal,
   ): Promise<ToolCallConfirmationDetails | false> {
     const correctedContentResult = await getCorrectedFileContent(
       this.config,
       this.resolvedPath,
       this.params.content,
-      _abortSignal,
+      abortSignal,
     );
 
     if (correctedContentResult.error) {