diff --git a/packages/ui/src/components/message-block.tsx b/packages/ui/src/components/message-block.tsx
index 07d6a9af..f24d6a99 100644
--- a/packages/ui/src/components/message-block.tsx
+++ b/packages/ui/src/components/message-block.tsx
@@ -28,7 +28,6 @@ function DeleteUpToIcon() {
   )
 }
 
-const TOOL_ICON = "🔧"
 const USER_BORDER_COLOR = "var(--message-user-border)"
 const ASSISTANT_BORDER_COLOR = "var(--message-assistant-border)"
 const TOOL_BORDER_COLOR = "var(--message-tool-border)"
@@ -612,8 +611,6 @@ function ToolCallItem(props: ToolCallItemProps) {
                 />
               </Show>
 
-              <span class="tool-call-icon">{TOOL_ICON}</span>
-              <span>{t("messageBlock.tool.header")}</span>
               <span class="tool-name">{toolName() || t("messageBlock.tool.unknown")}</span>
             </div>
 
diff --git a/packages/ui/src/components/tool-call.tsx b/packages/ui/src/components/tool-call.tsx
index af9be1eb..376cffeb 100644
--- a/packages/ui/src/components/tool-call.tsx
+++ b/packages/ui/src/components/tool-call.tsx
@@ -29,6 +29,7 @@ import type {
   ToolScrollHelpers,
 } from "./tool-call/types"
 import {
+  buildToolPreview,
   buildToolSpeechText,
   ensureMarkdownContent,
   getRelativePath,
@@ -606,7 +607,7 @@ export default function ToolCall(props: ToolCallProps) {
     return undefined
   })
 
-  const toolOutputDefaultExpanded = createMemo(() => (preferences().toolOutputExpansion || "expanded") === "expanded")
+  const toolOutputDefaultExpanded = createMemo(() => (preferences().toolOutputExpansion || "collapsed") === "expanded")
   const diagnosticsDefaultExpanded = createMemo(() => (preferences().diagnosticsExpansion || "expanded") === "expanded")
 
   const defaultExpandedForTool = createMemo(() => {
@@ -678,6 +679,7 @@ export default function ToolCall(props: ToolCallProps) {
   const [toolCallRootEl, setToolCallRootEl] = createSignal<HTMLDivElement | undefined>()
   const [scrollTopSnapshot, setScrollTopSnapshot] = createSignal(0)
   const [diagnosticsOverride, setDiagnosticsOverride] = createSignal<boolean | undefined>(undefined)
+  const collapsedPreview = createMemo(() => buildToolPreview(toolName(), toolState()))
 
   const diagnosticsExpanded = () => {
     if (isPermissionActive() || isQuestionActive()) return true
@@ -864,19 +866,18 @@ export default function ToolCall(props: ToolCallProps) {
   const status = () => toolState()?.status || ""
 
   return (
-      <div
-
-        ref={(element) => {
+    <div
+      ref={(element) => {
         setToolCallRootEl(element || undefined)
       }}
       class={`tool-call ${combinedStatusClass()}`}
       data-part-type="tool"
       data-tool-name={toolName()}
       data-instance-id={props.instanceId}
-        data-session-id={props.sessionId}
-        data-message-id={props.messageId}
-        data-part-id={toolCallIdentifier()}
-      >
+      data-session-id={props.sessionId}
+      data-message-id={props.messageId}
+      data-part-id={toolCallIdentifier()}
+    >
       <div class="tool-call-header" data-action-overflow={actionMenuItems().length > 1 ? "true" : undefined}>
         <button
           type="button"
@@ -885,7 +886,7 @@ export default function ToolCall(props: ToolCallProps) {
           aria-expanded={expanded()}
         >
           <span class="tool-call-summary" data-tool-icon={getToolIcon(toolName())}>
-            {headerText()}
+            <span class="tool-call-summary-text">{headerText()}</span>
           </span>
         </button>
 
@@ -969,9 +970,19 @@ export default function ToolCall(props: ToolCallProps) {
           setScrollTopSnapshot={setScrollTopSnapshot}
         />
       </Show>
- 
-      <Show when={diagnosticsEntries().length}>
 
+      <Show when={!expanded() && collapsedPreview()}>
+        {(preview) => (
+          <div class="tool-call-preview">
+            <div class="tool-call-preview-label">
+              {preview().kind === "output" ? t("toolCall.io.output") : t("toolCall.io.input")}
+            </div>
+            <div class="tool-call-preview-text">{preview().text}</div>
+          </div>
+        )}
+      </Show>
+
+      <Show when={diagnosticsEntries().length}>
         {renderDiagnosticsSection(
           t,
           diagnosticsEntries(),
diff --git a/packages/ui/src/components/tool-call/utils.ts b/packages/ui/src/components/tool-call/utils.ts
index 766d8d99..4c52dab7 100644
--- a/packages/ui/src/components/tool-call/utils.ts
+++ b/packages/ui/src/components/tool-call/utils.ts
@@ -152,6 +152,97 @@ export function formatUnknown(value: unknown): { text: string; language?: string
   return null
 }
 
+function joinPreviewParts(...parts: Array<string | undefined>): string | null {
+  const text = parts
+    .map((part) => (typeof part === "string" ? part.trim() : ""))
+    .filter(Boolean)
+    .join("\n")
+
+  return text.length > 0 ? text : null
+}
+
+function getToolInputPreview(toolName: string, input: Record<string, any>): unknown {
+  switch (toolName) {
+    case "bash":
+      return joinPreviewParts(
+        typeof input.command === "string" ? `$ ${input.command}` : undefined,
+        typeof input.description === "string" ? input.description : undefined,
+      )
+    case "read":
+    case "edit":
+    case "write":
+    case "patch":
+    case "apply_patch":
+    case "list":
+      return typeof input.filePath === "string"
+        ? input.filePath
+        : typeof input.path === "string"
+          ? input.path
+          : input
+    case "glob":
+      return joinPreviewParts(
+        typeof input.pattern === "string" ? input.pattern : undefined,
+        typeof input.path === "string" ? input.path : undefined,
+      )
+    case "grep":
+      return joinPreviewParts(
+        typeof input.pattern === "string" ? input.pattern : undefined,
+        typeof input.include === "string" ? input.include : undefined,
+        typeof input.path === "string" ? input.path : undefined,
+      )
+    case "webfetch":
+      return typeof input.url === "string" ? input.url : input
+    case "task":
+      return joinPreviewParts(
+        typeof input.description === "string" ? input.description : undefined,
+        typeof input.prompt === "string" ? input.prompt : undefined,
+      )
+    default:
+      return input
+  }
+}
+
+function formatPreviewText(value: unknown): string | null {
+  if (Array.isArray(value) && value.length === 0) {
+    return null
+  }
+
+  if (value && typeof value === "object" && Object.keys(value as Record<string, unknown>).length === 0) {
+    return null
+  }
+
+  const formatted = formatUnknown(value)
+  const text = formatted?.text?.trim()
+  return text ? text : null
+}
+
+export function buildToolPreview(toolName: string, state?: ToolState): {
+  kind: "input" | "output"
+  text: string
+} | null {
+  const { input, metadata } = readToolStatePayload(state)
+
+  const outputCandidate = !state
+    ? undefined
+    : isToolStateCompleted(state)
+      ? state.output ?? metadata.output ?? metadata.diff ?? metadata.preview
+      : isToolStateRunning(state) || isToolStateError(state)
+        ? metadata.output ?? metadata.diff ?? metadata.preview
+        : metadata.preview ?? metadata.diff
+
+  const outputText = formatPreviewText(outputCandidate)
+  if (outputText) {
+    return { kind: "output", text: outputText }
+  }
+
+  const inputText = formatPreviewText(getToolInputPreview(toolName, input))
+  if (inputText) {
+    return { kind: "input", text: inputText }
+  }
+
+  return null
+}
+
 export function inferLanguageFromPath(path?: string): string | undefined {
   return getLanguageFromPath(path || "")
 }
diff --git a/packages/ui/src/lib/settings/behavior-registry.ts b/packages/ui/src/lib/settings/behavior-registry.ts
index 25bd13e4..07054f63 100644
--- a/packages/ui/src/lib/settings/behavior-registry.ts
+++ b/packages/ui/src/lib/settings/behavior-registry.ts
@@ -182,7 +182,7 @@ export function getBehaviorSettings(actions: BehaviorRegistryActions): BehaviorS
       id: "behavior.toolOutputsDefault",
       titleKey: "settings.behavior.toolOutputsDefault.title",
       subtitleKey: "settings.behavior.toolOutputsDefault.subtitle",
-      get: (p) => (p.toolOutputExpansion ?? "expanded") as ExpansionPreference,
+      get: (p) => (p.toolOutputExpansion ?? "collapsed") as ExpansionPreference,
       set: (next) => {
         if (updatePreferences) {
           updatePreferences({ toolOutputExpansion: next as ExpansionPreference })
@@ -418,7 +418,7 @@ export function getBehaviorCommands(actions: BehaviorRegistryActions): Command[]
     {
       id: "tool-output-default-visibility",
       label: () => {
-        const mode = actions.preferences().toolOutputExpansion || "expanded"
+        const mode = actions.preferences().toolOutputExpansion || "collapsed"
         const state = mode === "expanded" ? tGlobal("commands.common.expanded") : tGlobal("commands.common.collapsed")
         return tGlobal("commands.toolOutputsDefault.label", { state })
       },
@@ -426,7 +426,7 @@ export function getBehaviorCommands(actions: BehaviorRegistryActions): Command[]
       category: "System",
       keywords: () => splitKeywords("commands.toolOutputsDefault.keywords"),
       action: () => {
-        const mode = actions.preferences().toolOutputExpansion || "expanded"
+        const mode = actions.preferences().toolOutputExpansion || "collapsed"
         const next: ExpansionPreference = mode === "expanded" ? "collapsed" : "expanded"
         actions.setToolOutputExpansion(next)
       },
diff --git a/packages/ui/src/stores/preferences.tsx b/packages/ui/src/stores/preferences.tsx
index a39b0796..7eb2fd89 100644
--- a/packages/ui/src/stores/preferences.tsx
+++ b/packages/ui/src/stores/preferences.tsx
@@ -141,7 +141,7 @@ const defaultUiSettings: UiSettings = {
   promptSubmitOnEnter: false,
   showPromptVoiceInput: true,
   diffViewMode: "split",
-  toolOutputExpansion: "expanded",
+  toolOutputExpansion: "collapsed",
   diagnosticsExpansion: "expanded",
   toolInputsVisibility: "collapsed",
   showUsageMetrics: true,
diff --git a/packages/ui/src/styles/messaging/tool-call.css b/packages/ui/src/styles/messaging/tool-call.css
index 3758cd52..0f6df2e4 100644
--- a/packages/ui/src/styles/messaging/tool-call.css
+++ b/packages/ui/src/styles/messaging/tool-call.css
@@ -17,6 +17,7 @@
 
 .tool-call-header-meta {
   @apply flex items-center gap-2;
+  min-width: 0;
 }
 
 .tool-call-header-button {
@@ -61,10 +62,6 @@
   display: inline-flex;
 }
 
-.tool-call-header-label .tool-call-icon {
-  @apply text-base;
-}
-
 .tool-call-header-label .tool-name {
   font-family: var(--font-family-mono);
   color: inherit;
@@ -99,6 +96,7 @@
   background-color: transparent;
   color: var(--text-primary);
   border-bottom: 1px solid var(--tool-call-border-color);
+  min-width: 0;
 }
 
 .tool-call-header:hover {
@@ -112,6 +110,7 @@
   border-radius: 0;
   color: var(--text-primary);
   flex: 1;
+  min-width: 0;
 }
 
 .tool-call-header-toggle::before {
@@ -186,6 +185,14 @@
 .tool-call-summary {
   @apply flex-1 text-start inline-flex items-center gap-2;
   color: var(--text-primary);
+  min-width: 0;
+}
+
+.tool-call-summary-text {
+  min-width: 0;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
 }
 
 .tool-call-summary::before {
@@ -247,7 +254,7 @@
   white-space: pre-wrap;
   word-wrap: break-word;
   overflow-wrap: break-word;
-  max-height: var(--tool-call-max-height-compact, calc(25 * 1.4em));
+  max-height: calc(6 * var(--tool-call-line-unit));
   overflow-y: scroll;
 }