diff --git a/frontend/src/core/components/tools/automate/ToolConfigurationModal.tsx b/frontend/src/core/components/tools/automate/ToolConfigurationModal.tsx
index a4b415856..fbb51467a 100644
--- a/frontend/src/core/components/tools/automate/ToolConfigurationModal.tsx
+++ b/frontend/src/core/components/tools/automate/ToolConfigurationModal.tsx
@@ -41,13 +41,16 @@ export default function ToolConfigurationModal({ opened, tool, onSave, onCancel,
 
   // Initialize parameters from tool (which should contain defaults from registry)
   useEffect(() => {
+    const toolConfig = toolRegistry[tool.operation as ToolId]?.operationConfig;
+    const defaultParams = toolConfig?.defaultParameters || {};
+
     if (tool.parameters) {
-      setParameters(tool.parameters);
+      setParameters({ ...defaultParams, ...tool.parameters });
     } else {
-      // Fallback to empty parameters if none provided
-      setParameters({});
+      // Fallback to default parameters if none provided
+      setParameters({ ...defaultParams });
     }
-  }, [tool.parameters, tool.operation]);
+  }, [tool.parameters, tool.operation, toolRegistry]);
 
   // Render the settings component
   const renderToolSettings = () => {
diff --git a/frontend/src/core/hooks/tools/addWatermark/useAddWatermarkOperation.ts b/frontend/src/core/hooks/tools/addWatermark/useAddWatermarkOperation.ts
index 6dcdec4eb..a02b95290 100644
--- a/frontend/src/core/hooks/tools/addWatermark/useAddWatermarkOperation.ts
+++ b/frontend/src/core/hooks/tools/addWatermark/useAddWatermarkOperation.ts
@@ -18,7 +18,7 @@ export const buildAddWatermarkFormData = (parameters: AddWatermarkParameters, fi
     formData.append("watermarkImage", parameters.watermarkImage);
   }
 
-  // Required parameters with correct formatting
+  // Required parameters with correct formatting (defaults merged in automationExecutor)
   formData.append("fontSize", parameters.fontSize.toString());
   formData.append("rotation", parameters.rotation.toString());
   formData.append("opacity", (parameters.opacity / 100).toString()); // Convert percentage to decimal
@@ -26,9 +26,9 @@ export const buildAddWatermarkFormData = (parameters: AddWatermarkParameters, fi
   formData.append("heightSpacer", parameters.heightSpacer.toString());
 
   // Backend-expected parameters from user input
-  formData.append("alphabet", parameters.alphabet);
-  formData.append("customColor", parameters.customColor);
-  formData.append("convertPDFToImage", parameters.convertPDFToImage.toString());
+  formData.append("alphabet", parameters.alphabet || "");
+  formData.append("customColor", parameters.customColor || "");
+  formData.append("convertPDFToImage", (parameters.convertPDFToImage ?? false).toString());
 
   return formData;
 };
diff --git a/frontend/src/core/hooks/tools/automate/useAutomateOperation.ts b/frontend/src/core/hooks/tools/automate/useAutomateOperation.ts
index f6fbcacda..d88507636 100644
--- a/frontend/src/core/hooks/tools/automate/useAutomateOperation.ts
+++ b/frontend/src/core/hooks/tools/automate/useAutomateOperation.ts
@@ -38,7 +38,7 @@ export function useAutomateOperation() {
     console.log(`✅ Automation completed, returning ${finalResults.length} files`);
     return {
       files: finalResults,
-      consumedAllInputs: false,
+      consumedAllInputs: true,
     };
   }, [toolRegistry]);
 
@@ -46,5 +46,6 @@ export function useAutomateOperation() {
     toolType: ToolType.custom,
     operationType: 'automate',
     customProcessor,
+    consumesAllInputs: true,
   });
 }
diff --git a/frontend/src/core/hooks/tools/automate/useAutomationForm.ts b/frontend/src/core/hooks/tools/automate/useAutomationForm.ts
index c86d112d6..3bcfad53b 100644
--- a/frontend/src/core/hooks/tools/automate/useAutomationForm.ts
+++ b/frontend/src/core/hooks/tools/automate/useAutomationForm.ts
@@ -52,7 +52,7 @@ export function useAutomationForm({ mode, existingAutomation, toolRegistry }: Us
           operation: operation,
           name: getToolName(operation),
           configured: isConfigured,
-          parameters: typeof op === 'object' ? op.parameters || {} : {}
+          parameters: typeof op === 'object' ? { ...getToolDefaultParameters(operation), ...(op.parameters || {}) } : getToolDefaultParameters(operation)
         };
       });
 
@@ -68,7 +68,7 @@ export function useAutomationForm({ mode, existingAutomation, toolRegistry }: Us
       }));
       setSelectedTools(defaultTools);
     }
-  }, [mode, existingAutomation, t, getToolName]);
+  }, [mode, existingAutomation, t, getToolName, getToolDefaultParameters]);
 
   const addTool = (operation: string) => {
     const toolEntry = toolRegistry[operation as ToolId];
diff --git a/frontend/src/core/hooks/tools/changePermissions/useChangePermissionsOperation.ts b/frontend/src/core/hooks/tools/changePermissions/useChangePermissionsOperation.ts
index 6e391f739..e854b5865 100644
--- a/frontend/src/core/hooks/tools/changePermissions/useChangePermissionsOperation.ts
+++ b/frontend/src/core/hooks/tools/changePermissions/useChangePermissionsOperation.ts
@@ -3,11 +3,12 @@ import { ToolType, useToolOperation } from '@app/hooks/tools/shared/useToolOpera
 import { createStandardErrorHandler } from '@app/utils/toolErrorHandler';
 import { ChangePermissionsParameters, defaultParameters } from '@app/hooks/tools/changePermissions/useChangePermissionsParameters';
 
-export const getFormData = ((parameters: ChangePermissionsParameters) =>
-  Object.entries(parameters).map(([key, value]) =>
-    [key, value.toString()]
-  ) as string[][]
-);
+export const getFormData = ((parameters: ChangePermissionsParameters) => {
+  if (!parameters) return [];
+  return Object.entries(parameters).map(([key, value]) =>
+    [key, (value ?? false).toString()]
+  ) as string[][];
+});
 
 // Static function that can be used by both the hook and automation executor
 export const buildChangePermissionsFormData = (parameters: ChangePermissionsParameters, file: File): FormData => {
diff --git a/frontend/src/core/hooks/tools/compress/useCompressOperation.ts b/frontend/src/core/hooks/tools/compress/useCompressOperation.ts
index e1dda9d0f..c10bea535 100644
--- a/frontend/src/core/hooks/tools/compress/useCompressOperation.ts
+++ b/frontend/src/core/hooks/tools/compress/useCompressOperation.ts
@@ -18,7 +18,7 @@ export const buildCompressFormData = (parameters: CompressParameters, file: File
     }
   }
 
-  formData.append("grayscale", parameters.grayscale.toString());
+  formData.append("grayscale", (parameters.grayscale ?? false).toString());
   formData.append("lineArt", parameters.lineArt.toString());
   formData.append("linearize", parameters.linearize.toString());
   if (parameters.lineArt) {
diff --git a/frontend/src/core/hooks/tools/merge/useMergeOperation.ts b/frontend/src/core/hooks/tools/merge/useMergeOperation.ts
index e21814a4f..3bed21479 100644
--- a/frontend/src/core/hooks/tools/merge/useMergeOperation.ts
+++ b/frontend/src/core/hooks/tools/merge/useMergeOperation.ts
@@ -1,7 +1,7 @@
 import { useTranslation } from 'react-i18next';
 import { useToolOperation, ToolOperationConfig, ToolType } from '@app/hooks/tools/shared/useToolOperation';
 import { createStandardErrorHandler } from '@app/utils/toolErrorHandler';
-import { MergeParameters } from '@app/hooks/tools/merge/useMergeParameters';
+import { MergeParameters, defaultParameters } from '@app/hooks/tools/merge/useMergeParameters';
 
 const buildFormData = (parameters: MergeParameters, files: File[]): FormData => {
   const formData = new FormData();
@@ -13,8 +13,8 @@ const buildFormData = (parameters: MergeParameters, files: File[]): FormData =>
   const clientIds: string[] = files.map((f: any) => String((f as any).fileId || f.name));
   formData.append('clientFileIds', JSON.stringify(clientIds));
   formData.append("sortType", "orderProvided"); // Always use orderProvided since UI handles sorting
-  formData.append("removeCertSign", parameters.removeDigitalSignature.toString());
-  formData.append("generateToc", parameters.generateTableOfContents.toString());
+  formData.append("removeCertSign", (parameters.removeDigitalSignature ?? false).toString());
+  formData.append("generateToc", (parameters.generateTableOfContents ?? false).toString());
 
   return formData;
 };
@@ -26,6 +26,7 @@ export const mergeOperationConfig: ToolOperationConfig<MergeParameters> = {
   operationType: 'merge',
   endpoint: '/api/v1/general/merge-pdfs',
   filePrefix: 'merged_',
+  defaultParameters,
 };
 
 export const useMergeOperation = () => {
diff --git a/frontend/src/core/hooks/tools/ocr/useOCROperation.ts b/frontend/src/core/hooks/tools/ocr/useOCROperation.ts
index 6e86a083e..8b3950e7f 100644
--- a/frontend/src/core/hooks/tools/ocr/useOCROperation.ts
+++ b/frontend/src/core/hooks/tools/ocr/useOCROperation.ts
@@ -44,11 +44,13 @@ export const buildOCRFormData = (parameters: OCRParameters, file: File): FormDat
   parameters.languages.forEach((lang) => formData.append('languages', lang));
   formData.append('ocrType', parameters.ocrType);
   formData.append('ocrRenderType', parameters.ocrRenderType);
-  formData.append('sidecar', parameters.additionalOptions.includes('sidecar').toString());
-  formData.append('deskew', parameters.additionalOptions.includes('deskew').toString());
-  formData.append('clean', parameters.additionalOptions.includes('clean').toString());
-  formData.append('cleanFinal', parameters.additionalOptions.includes('cleanFinal').toString());
-  formData.append('removeImagesAfter', parameters.additionalOptions.includes('removeImagesAfter').toString());
+  
+  const options = parameters.additionalOptions || [];
+  formData.append('sidecar', options.includes('sidecar').toString());
+  formData.append('deskew', options.includes('deskew').toString());
+  formData.append('clean', options.includes('clean').toString());
+  formData.append('cleanFinal', options.includes('cleanFinal').toString());
+  formData.append('removeImagesAfter', options.includes('removeImagesAfter').toString());
   return formData;
 };
 
diff --git a/frontend/src/core/hooks/tools/sanitize/useSanitizeOperation.ts b/frontend/src/core/hooks/tools/sanitize/useSanitizeOperation.ts
index 580fabe31..b4de35601 100644
--- a/frontend/src/core/hooks/tools/sanitize/useSanitizeOperation.ts
+++ b/frontend/src/core/hooks/tools/sanitize/useSanitizeOperation.ts
@@ -9,12 +9,12 @@ export const buildSanitizeFormData = (parameters: SanitizeParameters, file: File
   formData.append('fileInput', file);
 
   // Add parameters
-  formData.append('removeJavaScript', parameters.removeJavaScript.toString());
-  formData.append('removeEmbeddedFiles', parameters.removeEmbeddedFiles.toString());
-  formData.append('removeXMPMetadata', parameters.removeXMPMetadata.toString());
-  formData.append('removeMetadata', parameters.removeMetadata.toString());
-  formData.append('removeLinks', parameters.removeLinks.toString());
-  formData.append('removeFonts', parameters.removeFonts.toString());
+  formData.append('removeJavaScript', (parameters.removeJavaScript ?? false).toString());
+  formData.append('removeEmbeddedFiles', (parameters.removeEmbeddedFiles ?? false).toString());
+  formData.append('removeXMPMetadata', (parameters.removeXMPMetadata ?? false).toString());
+  formData.append('removeMetadata', (parameters.removeMetadata ?? false).toString());
+  formData.append('removeLinks', (parameters.removeLinks ?? false).toString());
+  formData.append('removeFonts', (parameters.removeFonts ?? false).toString());
 
   return formData;
 };
diff --git a/frontend/src/core/hooks/tools/shared/useToolOperation.ts b/frontend/src/core/hooks/tools/shared/useToolOperation.ts
index 4804032d0..b4881408a 100644
--- a/frontend/src/core/hooks/tools/shared/useToolOperation.ts
+++ b/frontend/src/core/hooks/tools/shared/useToolOperation.ts
@@ -71,6 +71,13 @@ interface BaseToolOperationConfig<TParams> {
 
   /** Default parameter values for automation */
   defaultParameters?: TParams;
+
+  /**
+   * For custom tools: if true, success implies all input files were successfully processed.
+   * Use this for tools like Automate or Merge where Many-to-One relationships exist
+   * and exact input-output mapping is difficult.
+   */
+  consumesAllInputs?: boolean;
 }
 
 export interface SingleFileToolOperationConfig<TParams> extends BaseToolOperationConfig<TParams> {
diff --git a/frontend/src/core/hooks/tools/split/useSplitOperation.ts b/frontend/src/core/hooks/tools/split/useSplitOperation.ts
index 1392900c9..425948683 100644
--- a/frontend/src/core/hooks/tools/split/useSplitOperation.ts
+++ b/frontend/src/core/hooks/tools/split/useSplitOperation.ts
@@ -19,7 +19,7 @@ export const buildSplitFormData = (parameters: SplitParameters, file: File): For
     case SPLIT_METHODS.BY_SECTIONS:
       formData.append("horizontalDivisions", parameters.hDiv);
       formData.append("verticalDivisions", parameters.vDiv);
-      formData.append("merge", parameters.merge.toString());
+      formData.append("merge", (parameters.merge ?? false).toString());
       formData.append("splitMode", parameters.splitMode || 'SPLIT_ALL');
       if (parameters.splitMode === 'CUSTOM' && parameters.customPages) {
         formData.append("pageNumbers", parameters.customPages);
@@ -39,11 +39,11 @@ export const buildSplitFormData = (parameters: SplitParameters, file: File): For
       break;
     case SPLIT_METHODS.BY_CHAPTERS:
       formData.append("bookmarkLevel", parameters.bookmarkLevel);
-      formData.append("includeMetadata", parameters.includeMetadata.toString());
-      formData.append("allowDuplicates", parameters.allowDuplicates.toString());
+      formData.append("includeMetadata", (parameters.includeMetadata ?? false).toString());
+      formData.append("allowDuplicates", (parameters.allowDuplicates ?? false).toString());
       break;
     case SPLIT_METHODS.BY_PAGE_DIVIDER:
-      formData.append("duplexMode", parameters.duplexMode.toString());
+      formData.append("duplexMode", (parameters.duplexMode ?? false).toString());
       break;
     default:
       throw new Error(`Unknown split method: ${parameters.method}`);
diff --git a/frontend/src/core/utils/automationExecutor.ts b/frontend/src/core/utils/automationExecutor.ts
index 2651784e1..7f8801559 100644
--- a/frontend/src/core/utils/automationExecutor.ts
+++ b/frontend/src/core/utils/automationExecutor.ts
@@ -155,18 +155,21 @@ export const executeToolOperationWithPrefix = async (
     throw new Error(`Tool operation not supported: ${operationName}`);
   }
 
+  // Merge with default parameters to ensure all required fields are present
+  const mergedParameters = { ...config.defaultParameters, ...parameters };
+
   try {
     // Check if tool uses custom processor (like Convert tool)
     if (config.customProcessor) {
-      const result = await config.customProcessor(parameters, files);
+      const result = await config.customProcessor(mergedParameters, files);
       return result.files;
     }
 
     // Execute based on tool type
     if (config.toolType === ToolType.multiFile) {
-      return await executeMultiFileOperation(config, parameters, files, filePrefix);
+      return await executeMultiFileOperation(config, mergedParameters, files, filePrefix);
     } else {
-      return await executeSingleFileOperation(config, parameters, files, filePrefix);
+      return await executeSingleFileOperation(config, mergedParameters, files, filePrefix);
     }
 
   } catch (error: any) {