diff --git a/web/src/components/workflows/ActionPalette.tsx b/web/src/components/workflows/ActionPalette.tsx
index 2aaf4fb..471588d 100644
--- a/web/src/components/workflows/ActionPalette.tsx
+++ b/web/src/components/workflows/ActionPalette.tsx
@@ -1,5 +1,11 @@
 import { useState, useMemo } from "react";
-import { Search, X, ChevronDown, ChevronRight, GripVertical } from "lucide-react";
+import {
+  Search,
+  X,
+  ChevronDown,
+  ChevronRight,
+  GripVertical,
+} from "lucide-react";
 import type { PaletteAction } from "@/types/workflow";
 
 interface ActionPaletteProps {
@@ -24,7 +30,7 @@ export default function ActionPalette({
         action.label?.toLowerCase().includes(query) ||
         action.ref?.toLowerCase().includes(query) ||
         action.description?.toLowerCase().includes(query) ||
-        action.pack_ref?.toLowerCase().includes(query)
+        action.pack_ref?.toLowerCase().includes(query),
     );
   }, [actions, searchQuery]);
 
@@ -38,7 +44,7 @@ export default function ActionPalette({
       grouped.get(packRef)!.push(action);
     });
     return new Map(
-      [...grouped.entries()].sort((a, b) => a[0].localeCompare(b[0]))
+      [...grouped.entries()].sort((a, b) => a[0].localeCompare(b[0])),
     );
   }, [filteredActions]);
 
@@ -55,7 +61,7 @@ export default function ActionPalette({
   };
 
   return (
-    <div className="w-64 border-r border-gray-200 bg-gray-50 flex flex-col h-full overflow-hidden">
+    <div className="flex flex-col h-full overflow-hidden">
       <div className="p-3 border-b border-gray-200 bg-white flex-shrink-0">
         <h3 className="text-sm font-semibold text-gray-700 uppercase tracking-wider mb-2">
           Action Palette
@@ -93,7 +99,9 @@ export default function ActionPalette({
           </div>
         ) : filteredActions.length === 0 ? (
           <div className="text-center py-8">
-            <p className="text-xs text-gray-500">No actions match your search</p>
+            <p className="text-xs text-gray-500">
+              No actions match your search
+            </p>
             <button
               onClick={() => setSearchQuery("")}
               className="mt-1 text-xs text-blue-600 hover:text-blue-800"
@@ -158,7 +166,7 @@ export default function ActionPalette({
                     )}
                   </div>
                 );
-              }
+              },
             )}
           </div>
         )}
diff --git a/web/src/components/workflows/WorkflowInputsPanel.tsx b/web/src/components/workflows/WorkflowInputsPanel.tsx
new file mode 100644
index 0000000..eb8d2d1
--- /dev/null
+++ b/web/src/components/workflows/WorkflowInputsPanel.tsx
@@ -0,0 +1,246 @@
+import { useState } from "react";
+import { Pencil, Plus, X, LogIn, LogOut } from "lucide-react";
+import SchemaBuilder from "@/components/common/SchemaBuilder";
+import type { ParamDefinition } from "@/types/workflow";
+
+interface WorkflowInputsPanelProps {
+  parameters: Record<string, ParamDefinition>;
+  output: Record<string, ParamDefinition>;
+  onParametersChange: (parameters: Record<string, ParamDefinition>) => void;
+  onOutputChange: (output: Record<string, ParamDefinition>) => void;
+}
+
+type ModalTarget = "parameters" | "output" | null;
+
+function ParamSummaryList({
+  schema,
+  emptyMessage,
+  onEdit,
+}: {
+  schema: Record<string, ParamDefinition>;
+  emptyMessage: string;
+  onEdit: () => void;
+}) {
+  const entries = Object.entries(schema);
+
+  if (entries.length === 0) {
+    return (
+      <button
+        onClick={onEdit}
+        className="w-full px-3 py-4 border-2 border-dashed border-gray-200 rounded-lg text-center hover:border-blue-300 hover:bg-blue-50/30 transition-colors group"
+      >
+        <Plus className="w-4 h-4 text-gray-300 group-hover:text-blue-400 mx-auto mb-1" />
+        <span className="text-[11px] text-gray-400 group-hover:text-blue-500">
+          {emptyMessage}
+        </span>
+      </button>
+    );
+  }
+
+  return (
+    <div className="space-y-1">
+      {entries.map(([name, def]) => (
+        <div
+          key={name}
+          className="flex items-center gap-1.5 px-2 py-1.5 bg-white border border-gray-150 rounded-md"
+        >
+          <div className="flex-1 min-w-0">
+            <div className="flex items-center gap-1.5">
+              <span className="font-mono text-[11px] font-medium text-gray-800 truncate">
+                {name}
+              </span>
+              {def.required && (
+                <span className="text-[9px] font-semibold text-red-500">*</span>
+              )}
+            </div>
+            <div className="flex items-center gap-1.5">
+              <span className="text-[10px] text-blue-600/70">{def.type}</span>
+              {def.secret && (
+                <span className="text-[9px] text-amber-500">secret</span>
+              )}
+              {def.default !== undefined && (
+                <span
+                  className="text-[9px] text-gray-400 truncate max-w-[80px]"
+                  title={`default: ${JSON.stringify(def.default)}`}
+                >
+                  = {JSON.stringify(def.default)}
+                </span>
+              )}
+            </div>
+          </div>
+        </div>
+      ))}
+      <button
+        onClick={onEdit}
+        className="flex items-center gap-1 px-2 py-1 text-[11px] text-gray-400 hover:text-blue-600 transition-colors w-full"
+      >
+        <Pencil className="w-3 h-3" />
+        Edit
+      </button>
+    </div>
+  );
+}
+
+export default function WorkflowInputsPanel({
+  parameters,
+  output,
+  onParametersChange,
+  onOutputChange,
+}: WorkflowInputsPanelProps) {
+  const [modalTarget, setModalTarget] = useState<ModalTarget>(null);
+
+  // Draft state for the modal so changes only apply on confirm
+  const [draftSchema, setDraftSchema] = useState<
+    Record<string, ParamDefinition>
+  >({});
+
+  const openModal = (target: ModalTarget) => {
+    if (target === "parameters") {
+      setDraftSchema({ ...parameters });
+    } else if (target === "output") {
+      setDraftSchema({ ...output });
+    }
+    setModalTarget(target);
+  };
+
+  const handleConfirm = () => {
+    if (modalTarget === "parameters") {
+      onParametersChange(draftSchema);
+    } else if (modalTarget === "output") {
+      onOutputChange(draftSchema);
+    }
+    setModalTarget(null);
+  };
+
+  const handleCancel = () => {
+    setModalTarget(null);
+  };
+
+  const modalLabel =
+    modalTarget === "parameters" ? "Input Parameters" : "Output";
+
+  return (
+    <>
+      <div className="flex flex-col h-full overflow-hidden">
+        <div className="flex-1 overflow-y-auto p-3 space-y-4">
+          {/* Input Parameters */}
+          <div>
+            <div className="flex items-center justify-between mb-1.5">
+              <div className="flex items-center gap-1.5">
+                <LogIn className="w-3.5 h-3.5 text-green-500" />
+                <h4 className="text-xs font-semibold text-gray-600 uppercase tracking-wider">
+                  Inputs
+                </h4>
+              </div>
+              {Object.keys(parameters).length > 0 && (
+                <span className="text-[10px] text-gray-400">
+                  {Object.keys(parameters).length}
+                </span>
+              )}
+            </div>
+            <p className="text-[10px] text-gray-400 mb-2">
+              Referenced via{" "}
+              <code className="px-0.5 bg-gray-100 rounded">
+                {"{{ params.<name> }}"}
+              </code>
+            </p>
+            <ParamSummaryList
+              schema={parameters}
+              emptyMessage="Add input parameters"
+              onEdit={() => openModal("parameters")}
+            />
+          </div>
+
+          {/* Output Schema */}
+          <div className="border-t border-gray-200 pt-3">
+            <div className="flex items-center justify-between mb-1.5">
+              <div className="flex items-center gap-1.5">
+                <LogOut className="w-3.5 h-3.5 text-violet-500" />
+                <h4 className="text-xs font-semibold text-gray-600 uppercase tracking-wider">
+                  Output
+                </h4>
+              </div>
+              {Object.keys(output).length > 0 && (
+                <span className="text-[10px] text-gray-400">
+                  {Object.keys(output).length}
+                </span>
+              )}
+            </div>
+            <p className="text-[10px] text-gray-400 mb-2">
+              Values this workflow produces on completion.
+            </p>
+            <ParamSummaryList
+              schema={output}
+              emptyMessage="Add output schema"
+              onEdit={() => openModal("output")}
+            />
+          </div>
+        </div>
+      </div>
+
+      {/* Full-screen modal for SchemaBuilder editing */}
+      {modalTarget && (
+        <div className="fixed inset-0 z-[70] flex items-center justify-center">
+          {/* Backdrop */}
+          <div
+            className="absolute inset-0 bg-black/40"
+            onClick={handleCancel}
+          />
+          {/* Modal */}
+          <div className="relative bg-white rounded-xl shadow-2xl border border-gray-200 flex flex-col w-full max-w-2xl max-h-[80vh] mx-4">
+            {/* Header */}
+            <div className="flex items-center justify-between px-6 py-4 border-b border-gray-200 flex-shrink-0">
+              <div>
+                <h2 className="text-base font-semibold text-gray-900">
+                  {modalLabel}
+                </h2>
+                <p className="text-xs text-gray-500 mt-0.5">
+                  {modalTarget === "parameters"
+                    ? "Define the inputs this workflow accepts when executed."
+                    : "Define the outputs this workflow produces upon completion."}
+                </p>
+              </div>
+              <button
+                onClick={handleCancel}
+                className="p-1.5 rounded-lg hover:bg-gray-100 text-gray-400 hover:text-gray-600 transition-colors"
+              >
+                <X className="w-5 h-5" />
+              </button>
+            </div>
+
+            {/* Body */}
+            <div className="flex-1 overflow-y-auto px-6 py-4">
+              <SchemaBuilder
+                value={draftSchema}
+                onChange={(schema) =>
+                  setDraftSchema(schema as Record<string, ParamDefinition>)
+                }
+                placeholder={
+                  modalTarget === "parameters"
+                    ? '{"message": {"type": "string", "required": true}}'
+                    : '{"result": {"type": "string"}}'
+                }
+              />
+            </div>
+
+            {/* Footer */}
+            <div className="flex items-center justify-end gap-2 px-6 py-3 border-t border-gray-200 bg-gray-50 rounded-b-xl flex-shrink-0">
+              <button
+                onClick={handleCancel}
+                className="px-4 py-2 text-sm font-medium text-gray-700 bg-white border border-gray-300 rounded-lg hover:bg-gray-50 transition-colors"
+              >
+                Cancel
+              </button>
+              <button
+                onClick={handleConfirm}
+                className="px-4 py-2 text-sm font-medium text-white bg-blue-600 rounded-lg hover:bg-blue-700 transition-colors shadow-sm"
+              >
+                Apply
+              </button>
+            </div>
+          </div>
+        </div>
+      )}
+    </>
+  );
+}
diff --git a/web/src/pages/actions/WorkflowBuilderPage.tsx b/web/src/pages/actions/WorkflowBuilderPage.tsx
index 2a14140..b69b835 100644
--- a/web/src/pages/actions/WorkflowBuilderPage.tsx
+++ b/web/src/pages/actions/WorkflowBuilderPage.tsx
@@ -9,10 +9,13 @@ import {
   Code,
   LayoutDashboard,
   X,
+  Zap,
+  Settings2,
 } from "lucide-react";
 import yaml from "js-yaml";
 import type { WorkflowYamlDefinition } from "@/types/workflow";
 import ActionPalette from "@/components/workflows/ActionPalette";
+import WorkflowInputsPanel from "@/components/workflows/WorkflowInputsPanel";
 import WorkflowCanvas from "@/components/workflows/WorkflowCanvas";
 import type { EdgeHoverInfo } from "@/components/workflows/WorkflowEdges";
 import TaskInspector from "@/components/workflows/TaskInspector";
@@ -83,6 +86,7 @@ export default function WorkflowBuilderPage() {
   const [saveSuccess, setSaveSuccess] = useState(false);
   const [initialized, setInitialized] = useState(false);
   const [showYamlPreview, setShowYamlPreview] = useState(false);
+  const [sidebarTab, setSidebarTab] = useState<"actions" | "inputs">("actions");
   const [highlightedTransition, setHighlightedTransition] = useState<{
     taskId: string;
     transitionIndex: number;
@@ -747,12 +751,59 @@ export default function WorkflowBuilderPage() {
           </div>
         ) : (
           <>
-            {/* Left: Action Palette */}
-            <ActionPalette
-              actions={paletteActions}
-              isLoading={actionsLoading}
-              onAddTask={handleAddTaskFromPalette}
-            />
+            {/* Left sidebar: tabbed Actions / Inputs */}
+            <div className="w-64 border-r border-gray-200 bg-gray-50 flex flex-col h-full overflow-hidden">
+              {/* Tab header */}
+              <div className="flex border-b border-gray-200 bg-white flex-shrink-0">
+                <button
+                  onClick={() => setSidebarTab("actions")}
+                  className={`flex-1 flex items-center justify-center gap-1.5 px-3 py-2 text-xs font-medium transition-colors ${
+                    sidebarTab === "actions"
+                      ? "text-blue-600 border-b-2 border-blue-600 bg-blue-50/50"
+                      : "text-gray-500 hover:text-gray-700 hover:bg-gray-50"
+                  }`}
+                >
+                  <Zap className="w-3.5 h-3.5" />
+                  Actions
+                </button>
+                <button
+                  onClick={() => setSidebarTab("inputs")}
+                  className={`flex-1 flex items-center justify-center gap-1.5 px-3 py-2 text-xs font-medium transition-colors ${
+                    sidebarTab === "inputs"
+                      ? "text-blue-600 border-b-2 border-blue-600 bg-blue-50/50"
+                      : "text-gray-500 hover:text-gray-700 hover:bg-gray-50"
+                  }`}
+                >
+                  <Settings2 className="w-3.5 h-3.5" />
+                  Inputs
+                  {Object.keys(state.parameters).length > 0 && (
+                    <span className="text-[10px] bg-blue-100 text-blue-700 px-1.5 py-0.5 rounded-full">
+                      {Object.keys(state.parameters).length}
+                    </span>
+                  )}
+                </button>
+              </div>
+
+              {/* Tab content */}
+              {sidebarTab === "actions" ? (
+                <ActionPalette
+                  actions={paletteActions}
+                  isLoading={actionsLoading}
+                  onAddTask={handleAddTaskFromPalette}
+                />
+              ) : (
+                <WorkflowInputsPanel
+                  parameters={state.parameters}
+                  output={state.output}
+                  onParametersChange={(parameters) =>
+                    setState((prev) => ({ ...prev, parameters }))
+                  }
+                  onOutputChange={(output) =>
+                    setState((prev) => ({ ...prev, output }))
+                  }
+                />
+              )}
+            </div>
 
             {/* Center: Canvas */}
             <WorkflowCanvas