diff --git a/docs/streaming-output.md b/docs/streaming-output.md
index d1a8365..6ef4a0b 100644
--- a/docs/streaming-output.md
+++ b/docs/streaming-output.md
@@ -4,7 +4,7 @@ Status: **Implemented**
 
 ## Overview
 
-Long-running Bazel commands (build, test, query, clean) can stream stdout/stderr incrementally instead of buffering the entire output until completion. This gives agents and CLI users real-time feedback on build progress.
+Long-running Bazel commands (build, test, query, clean) can stream stdout/stderr incrementally instead of buffering the entire output until completion. **Streaming is off by default** (`streaming: false`) to keep MCP tool responses compact. Opt in with `streaming: true` when you want live progress notifications.
 
 ## Supported Tools
 
@@ -18,7 +18,7 @@ Long-running Bazel commands (build, test, query, clean) can stream stdout/stderr
 
 ## MCP Protocol
 
-Set `streaming: true` in the tool arguments and include a `_meta.progressToken` in the request:
+Set `streaming: true` in the tool arguments (or via `bazel_ios_set_defaults`) and include a `_meta.progressToken` in the request:
 
 ```json
 {
diff --git a/src/runtime/config.ts b/src/runtime/config.ts
index 98467f2..70450ab 100644
--- a/src/runtime/config.ts
+++ b/src/runtime/config.ts
@@ -81,6 +81,7 @@ export function activateProfile(name: string): SessionDefaults {
     simulatorId: profile.defaultSimulatorId || config.defaults.simulatorId,
     buildMode: profile.defaultBuildMode || config.defaults.buildMode,
     platform: profile.defaultPlatform || config.defaults.platform,
+    streaming: profile.streaming ?? config.defaults.streaming,
   };
   return { ...config.defaults };
 }
@@ -141,6 +142,9 @@ function applyFileConfig(fileConfig: FileConfig, filePath: string): void {
   if (fileConfig.defaultTarget) {
     config.defaults.target = config.defaults.target || fileConfig.defaultTarget;
   }
+  if (fileConfig.defaultStreaming !== undefined && config.defaults.streaming === undefined) {
+    config.defaults.streaming = fileConfig.defaultStreaming;
+  }
   if (fileConfig.profiles) {
     config.profiles = { ...config.profiles, ...fileConfig.profiles };
   }
diff --git a/src/tools/bazel-tools.test.ts b/src/tools/bazel-tools.test.ts
index 316c271..858d025 100644
--- a/src/tools/bazel-tools.test.ts
+++ b/src/tools/bazel-tools.test.ts
@@ -330,6 +330,7 @@ describe('Bazel MCP tool definitions', () => {
       const properties = tool.inputSchema.properties as Record<string, unknown>;
       const streaming = properties.streaming as Record<string, unknown>;
       expect(streaming?.type, `${toolName} should expose streaming flag`).toBe('boolean');
+      expect(streaming?.default, `${toolName} streaming should default to false`).toBe(false);
     }
   });
 
diff --git a/src/tools/handlers/build.ts b/src/tools/handlers/build.ts
index c7eee10..8f386c6 100644
--- a/src/tools/handlers/build.ts
+++ b/src/tools/handlers/build.ts
@@ -32,6 +32,7 @@ import type {
 } from '../../types/index.js';
 import { formatCommandResult, structuredCommandResult, toolResult, toolText } from '../../utils/output.js';
 import { numberOrUndefined, prependWarning, resolveSimulatorFromArgs, stringOrUndefined } from '../helpers.js';
+import { STREAMING_PROPERTY } from '../schema-constants.js';
 
 interface LcovFile { name: string; total: number; covered: number }
 
@@ -92,7 +93,7 @@ export const definitions: ToolDefinition[] = [
         startupArgs: { type: 'array', items: { type: 'string' } },
         extraArgs: { type: 'array', items: { type: 'string' } },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream build output incrementally via progress notifications.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
@@ -126,7 +127,7 @@ export const definitions: ToolDefinition[] = [
           description: 'Environment variables injected into the launched app.',
         },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream build output incrementally via progress notifications.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
@@ -145,7 +146,7 @@ export const definitions: ToolDefinition[] = [
         startupArgs: { type: 'array', items: { type: 'string' } },
         extraArgs: { type: 'array', items: { type: 'string' } },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream test output incrementally via progress notifications.' },
+        streaming: STREAMING_PROPERTY,
         minimizeSimulator: {
           type: 'boolean',
           description: 'Minimize Simulator.app windows while the test runs.',
@@ -222,7 +223,7 @@ export const definitions: ToolDefinition[] = [
       properties: {
         expunge: { type: 'boolean', description: 'Remove entire output base (bazel clean --expunge).' },
         startupArgs: { type: 'array', items: { type: 'string' } },
-        streaming: { type: 'boolean', description: 'Stream output incrementally via progress notifications.' },
+        streaming: STREAMING_PROPERTY,
       },
     },
   },
diff --git a/src/tools/handlers/device.ts b/src/tools/handlers/device.ts
index 6f86bed..2a19235 100644
--- a/src/tools/handlers/device.ts
+++ b/src/tools/handlers/device.ts
@@ -24,6 +24,7 @@ import { findAppBundle, readBundleId } from '../../core/simulators.js';
 import { getConfig } from '../../runtime/config.js';
 import { formatCommandResult, structuredCommandResult, toolResult, toolText } from '../../utils/output.js';
 import { deviceLogCaptures, stringOrUndefined, numberOrUndefined } from '../helpers.js';
+import { STREAMING_PROPERTY } from '../schema-constants.js';
 
 export const definitions: ToolDefinition[] = [
   {
@@ -64,7 +65,7 @@ export const definitions: ToolDefinition[] = [
           description: 'Environment variables injected into the launched app on device.',
         },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream build output incrementally via progress notifications.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
@@ -133,7 +134,7 @@ export const definitions: ToolDefinition[] = [
         startupArgs: { type: 'array', items: { type: 'string' } },
         extraArgs: { type: 'array', items: { type: 'string' } },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream test output incrementally.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
diff --git a/src/tools/handlers/macos.ts b/src/tools/handlers/macos.ts
index f4aefe3..981b6d2 100644
--- a/src/tools/handlers/macos.ts
+++ b/src/tools/handlers/macos.ts
@@ -1,5 +1,6 @@
 import type { JsonObject, ToolCallResult, ToolDefinition, BuildArgs, TestArgs, TargetKind, BuildMode } from '../../types/index.js';
 import { stringOrUndefined, numberOrUndefined } from '../helpers.js';
+import { STREAMING_PROPERTY } from '../schema-constants.js';
 import { buildCommandArgs, configArgs, discoverExpression, modeArgs, requireLabel, runBazel, asStringArray, testFilterArgs } from '../../core/bazel.js';
 import { findAppBundle, readBundleId } from '../../core/simulators.js';
 import { formatCommandResult, structuredCommandResult, toolResult, toolText } from '../../utils/output.js';
@@ -19,7 +20,7 @@ export const definitions: ToolDefinition[] = [
         startupArgs: { type: 'array', items: { type: 'string' } },
         extraArgs: { type: 'array', items: { type: 'string' } },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream build output incrementally via progress notifications.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
@@ -37,7 +38,7 @@ export const definitions: ToolDefinition[] = [
         extraArgs: { type: 'array', items: { type: 'string' } },
         runArgs: { type: 'array', items: { type: 'string' }, description: 'Arguments passed to the launched binary after --.' },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream output incrementally via progress notifications.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
@@ -54,7 +55,7 @@ export const definitions: ToolDefinition[] = [
         startupArgs: { type: 'array', items: { type: 'string' } },
         extraArgs: { type: 'array', items: { type: 'string' } },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream test output incrementally via progress notifications.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
diff --git a/src/tools/handlers/multi-platform.ts b/src/tools/handlers/multi-platform.ts
index 119e950..aab9807 100644
--- a/src/tools/handlers/multi-platform.ts
+++ b/src/tools/handlers/multi-platform.ts
@@ -1,5 +1,6 @@
 import type { JsonObject, ToolCallResult, ToolDefinition, BuildArgs, TestArgs, BuildPlatform, BuildMode, TargetKind } from '../../types/index.js';
 import { stringOrUndefined, numberOrUndefined } from '../helpers.js';
+import { STREAMING_PROPERTY } from '../schema-constants.js';
 import { buildCommandArgs, configArgs, discoverExpression, modeArgs, platformArgs, requireLabel, runBazel, asStringArray, testFilterArgs } from '../../core/bazel.js';
 import { formatCommandResult, structuredCommandResult, toolResult, toolText } from '../../utils/output.js';
 
@@ -16,7 +17,7 @@ export const definitions: ToolDefinition[] = [
         startupArgs: { type: 'array', items: { type: 'string' } },
         extraArgs: { type: 'array', items: { type: 'string' } },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream build output incrementally.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
@@ -33,7 +34,7 @@ export const definitions: ToolDefinition[] = [
         startupArgs: { type: 'array', items: { type: 'string' } },
         extraArgs: { type: 'array', items: { type: 'string' } },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream test output incrementally.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
@@ -51,7 +52,7 @@ export const definitions: ToolDefinition[] = [
         extraArgs: { type: 'array', items: { type: 'string' } },
         runArgs: { type: 'array', items: { type: 'string' }, description: 'Arguments passed after --.' },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream output incrementally.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
@@ -81,7 +82,7 @@ export const definitions: ToolDefinition[] = [
         startupArgs: { type: 'array', items: { type: 'string' } },
         extraArgs: { type: 'array', items: { type: 'string' } },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream build output incrementally.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
@@ -98,7 +99,7 @@ export const definitions: ToolDefinition[] = [
         startupArgs: { type: 'array', items: { type: 'string' } },
         extraArgs: { type: 'array', items: { type: 'string' } },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream test output incrementally.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
@@ -116,7 +117,7 @@ export const definitions: ToolDefinition[] = [
         extraArgs: { type: 'array', items: { type: 'string' } },
         runArgs: { type: 'array', items: { type: 'string' }, description: 'Arguments passed after --.' },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream output incrementally.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
@@ -146,7 +147,7 @@ export const definitions: ToolDefinition[] = [
         startupArgs: { type: 'array', items: { type: 'string' } },
         extraArgs: { type: 'array', items: { type: 'string' } },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream build output incrementally.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
@@ -163,7 +164,7 @@ export const definitions: ToolDefinition[] = [
         startupArgs: { type: 'array', items: { type: 'string' } },
         extraArgs: { type: 'array', items: { type: 'string' } },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream test output incrementally.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
@@ -181,7 +182,7 @@ export const definitions: ToolDefinition[] = [
         extraArgs: { type: 'array', items: { type: 'string' } },
         runArgs: { type: 'array', items: { type: 'string' }, description: 'Arguments passed after --.' },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream output incrementally.' },
+        streaming: STREAMING_PROPERTY,
       },
       required: ['target'],
     },
diff --git a/src/tools/handlers/session.ts b/src/tools/handlers/session.ts
index 7c7cc8b..b153ca5 100644
--- a/src/tools/handlers/session.ts
+++ b/src/tools/handlers/session.ts
@@ -18,7 +18,7 @@ import {
 import type { BuildMode, BuildPlatform, JsonObject, ToolCallResult, ToolDefinition } from '../../types/index.js';
 import { formatCommandResult, toolText } from '../../utils/output.js';
 import { runCommand } from '../../utils/process.js';
-import { stringOrUndefined } from '../helpers.js';
+import { stringOrUndefined, booleanOrUndefined } from '../helpers.js';
 import { bazelToolDefinitions } from '../bazel-tools.js';
 
 export const definitions: ToolDefinition[] = [
@@ -50,6 +50,10 @@ export const definitions: ToolDefinition[] = [
         simulatorId: { type: 'string', description: 'Default simulator UDID.' },
         buildMode: { type: 'string', enum: ['none', 'debug', 'release', 'release_with_symbols'] },
         platform: { type: 'string', enum: ['none', 'simulator', 'device'] },
+        streaming: {
+          type: 'boolean',
+          description: 'Default streaming for build/test tools. Defaults to false. Set true for live progress.',
+        },
         profile: { type: 'string', description: 'Activate a named profile from config file.' },
         clear: { type: 'boolean', description: 'Clear all session defaults.' },
       },
@@ -194,6 +198,7 @@ export async function handle(name: string, args: JsonObject): Promise<ToolCallRe
         simulatorId: stringOrUndefined(args.simulatorId),
         buildMode: stringOrUndefined(args.buildMode) as BuildMode | undefined,
         platform: stringOrUndefined(args.platform) as BuildPlatform | undefined,
+        streaming: booleanOrUndefined(args.streaming),
       });
       const lines = Object.entries(updated)
         .filter(([, v]) => v !== undefined)
diff --git a/src/tools/handlers/spm.ts b/src/tools/handlers/spm.ts
index 039215a..c3224fa 100644
--- a/src/tools/handlers/spm.ts
+++ b/src/tools/handlers/spm.ts
@@ -5,6 +5,7 @@ import { runCommand } from '../../utils/process.js';
 import { formatCommandResult, structuredCommandResult, toolResult, toolText } from '../../utils/output.js';
 import { getConfig } from '../../runtime/config.js';
 import { stringOrUndefined, numberOrUndefined } from '../helpers.js';
+import { STREAMING_PROPERTY } from '../schema-constants.js';
 import { asStringArray } from '../../core/bazel.js';
 
 export const definitions: ToolDefinition[] = [
@@ -19,7 +20,7 @@ export const definitions: ToolDefinition[] = [
         target: { type: 'string', description: 'Specific target to build (default: all targets).' },
         extraArgs: { type: 'array', items: { type: 'string' }, description: 'Additional arguments passed to swift build.' },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream build output incrementally via progress notifications.' },
+        streaming: STREAMING_PROPERTY,
       },
     },
   },
@@ -34,7 +35,7 @@ export const definitions: ToolDefinition[] = [
         configuration: { type: 'string', enum: ['debug', 'release'], description: 'Build configuration (default: debug).' },
         extraArgs: { type: 'array', items: { type: 'string' }, description: 'Additional arguments passed to swift test.' },
         timeoutSeconds: { type: 'number' },
-        streaming: { type: 'boolean', description: 'Stream test output incrementally via progress notifications.' },
+        streaming: STREAMING_PROPERTY,
       },
     },
   },
diff --git a/src/tools/helpers.test.ts b/src/tools/helpers.test.ts
index a60708e..e8c9fd5 100644
--- a/src/tools/helpers.test.ts
+++ b/src/tools/helpers.test.ts
@@ -46,50 +46,50 @@ describe('prependWarning', () => {
 describe('applyDefaults', () => {
   afterEach(() => clearDefaults());
 
-  it('returns args unchanged when no defaults set', () => {
+  it('returns args with streaming=false when no defaults set', () => {
     clearDefaults();
     const args = { target: '//app' };
-    expect(applyDefaults(args)).toEqual({ target: '//app' });
+    expect(applyDefaults(args)).toEqual({ target: '//app', streaming: false });
   });
 
   it('merges target default when args.target is undefined', () => {
     setDefaults({ target: '//default' });
-    expect(applyDefaults({})).toEqual({ target: '//default' });
+    expect(applyDefaults({})).toEqual({ target: '//default', streaming: false });
   });
 
   it('does NOT override explicitly provided target', () => {
     setDefaults({ target: '//default' });
-    expect(applyDefaults({ target: '//explicit' })).toEqual({ target: '//explicit' });
+    expect(applyDefaults({ target: '//explicit' })).toEqual({ target: '//explicit', streaming: false });
   });
 
   it('merges simulatorName', () => {
     setDefaults({ simulatorName: 'iPhone 15' });
-    expect(applyDefaults({})).toEqual({ simulatorName: 'iPhone 15' });
+    expect(applyDefaults({})).toEqual({ simulatorName: 'iPhone 15', streaming: false });
   });
 
   it('merges simulatorId', () => {
     setDefaults({ simulatorId: 'ABC-123' });
-    expect(applyDefaults({})).toEqual({ simulatorId: 'ABC-123' });
+    expect(applyDefaults({})).toEqual({ simulatorId: 'ABC-123', streaming: false });
   });
 
   it('merges buildMode', () => {
     setDefaults({ buildMode: 'debug' });
-    expect(applyDefaults({})).toEqual({ buildMode: 'debug' });
+    expect(applyDefaults({})).toEqual({ buildMode: 'debug', streaming: false });
   });
 
   it('merges platform', () => {
     setDefaults({ platform: 'simulator' });
-    expect(applyDefaults({})).toEqual({ platform: 'simulator' });
+    expect(applyDefaults({})).toEqual({ platform: 'simulator', streaming: false });
   });
 
   it('does NOT merge buildMode=none', () => {
     setDefaults({ buildMode: 'none' });
-    expect(applyDefaults({})).toEqual({});
+    expect(applyDefaults({})).toEqual({ streaming: false });
   });
 
   it('does NOT merge platform=none', () => {
     setDefaults({ platform: 'none' });
-    expect(applyDefaults({})).toEqual({});
+    expect(applyDefaults({})).toEqual({ streaming: false });
   });
 
   it('handles multiple defaults at once', () => {
@@ -99,8 +99,19 @@ describe('applyDefaults', () => {
       simulatorName: 'iPhone 15',
       buildMode: 'debug',
       platform: 'simulator',
+      streaming: false,
     });
   });
+
+  it('merges streaming default from session', () => {
+    setDefaults({ streaming: true });
+    expect(applyDefaults({})).toEqual({ streaming: true });
+  });
+
+  it('does NOT override explicitly provided streaming', () => {
+    setDefaults({ streaming: true });
+    expect(applyDefaults({ streaming: false })).toEqual({ streaming: false });
+  });
 });
 
 describe('nextLogCaptureId', () => {
diff --git a/src/tools/helpers.ts b/src/tools/helpers.ts
index 4c16e86..1d08977 100644
--- a/src/tools/helpers.ts
+++ b/src/tools/helpers.ts
@@ -15,13 +15,13 @@ export const deviceLogCaptures = new Map<string, { child: ReturnType<typeof spaw
 
 export function applyDefaults(args: JsonObject): JsonObject {
   const defaults = getDefaults();
-  if (!defaults || Object.keys(defaults).length === 0) return args;
   const merged = { ...args };
   if (defaults.target && merged.target === undefined) merged.target = defaults.target;
   if (defaults.simulatorName && merged.simulatorName === undefined) merged.simulatorName = defaults.simulatorName;
   if (defaults.simulatorId && merged.simulatorId === undefined) merged.simulatorId = defaults.simulatorId;
   if (defaults.buildMode && defaults.buildMode !== 'none' && merged.buildMode === undefined) merged.buildMode = defaults.buildMode;
   if (defaults.platform && defaults.platform !== 'none' && merged.platform === undefined) merged.platform = defaults.platform;
+  if (merged.streaming === undefined) merged.streaming = defaults.streaming ?? false;
   return merged;
 }
 
@@ -45,3 +45,7 @@ export function numberOrUndefined(value: unknown): number | undefined {
   return typeof value === 'number' ? value : undefined;
 }
 
+export function booleanOrUndefined(value: unknown): boolean | undefined {
+  return typeof value === 'boolean' ? value : undefined;
+}
+
diff --git a/src/tools/schema-constants.ts b/src/tools/schema-constants.ts
new file mode 100644
index 0000000..0dcc3e3
--- /dev/null
+++ b/src/tools/schema-constants.ts
@@ -0,0 +1,8 @@
+import type { JsonObject } from '../types/index.js';
+
+export const STREAMING_PROPERTY: JsonObject = {
+  type: 'boolean',
+  description:
+    'Stream command output via MCP progress notifications. Defaults to false. Set true for live progress on long builds.',
+  default: false,
+};
diff --git a/src/types/index.ts b/src/types/index.ts
index d804a74..84169f8 100644
--- a/src/types/index.ts
+++ b/src/types/index.ts
@@ -24,6 +24,7 @@ export interface SessionDefaults {
   simulatorId?: string;
   buildMode?: BuildMode;
   platform?: BuildPlatform;
+  streaming?: boolean;
 }
 
 export interface ProfileConfig {
@@ -32,6 +33,7 @@ export interface ProfileConfig {
   defaultSimulatorId?: string;
   defaultBuildMode?: BuildMode;
   defaultPlatform?: BuildPlatform;
+  streaming?: boolean;
 }
 
 export interface FileConfig {
@@ -42,6 +44,7 @@ export interface FileConfig {
   defaultPlatform?: BuildPlatform;
   defaultBuildMode?: BuildMode;
   defaultTarget?: string;
+  defaultStreaming?: boolean;
   profiles?: Record<string, ProfileConfig>;
   enabledWorkflows?: string[];
 }