diff --git a/src/hooks/keyword-detector/constants.ts b/src/hooks/keyword-detector/constants.ts
index 6c9bec4a9..254bb4fa0 100644
--- a/src/hooks/keyword-detector/constants.ts
+++ b/src/hooks/keyword-detector/constants.ts
@@ -2,7 +2,7 @@ export const CODE_BLOCK_PATTERN = /```[\s\S]*?```/g
 export const INLINE_CODE_PATTERN = /`[^`]+`/g
 
 // Re-export from submodules
-export { isPlannerAgent, getUltraworkMessage } from "./ultrawork"
+export { isPlannerAgent, isNonOmoAgent, getUltraworkMessage } from "./ultrawork"
 export { SEARCH_PATTERN, SEARCH_MESSAGE } from "./search"
 export { ANALYZE_PATTERN, ANALYZE_MESSAGE } from "./analyze"
 
diff --git a/src/hooks/keyword-detector/hook.ts b/src/hooks/keyword-detector/hook.ts
index 8d7fcb15d..86e4eda73 100644
--- a/src/hooks/keyword-detector/hook.ts
+++ b/src/hooks/keyword-detector/hook.ts
@@ -1,6 +1,6 @@
 import type { PluginInput } from "@opencode-ai/plugin"
 import { detectKeywordsWithType, extractPromptText } from "./detector"
-import { isPlannerAgent } from "./constants"
+import { isPlannerAgent, isNonOmoAgent } from "./constants"
 import { log } from "../../shared"
 import {
   isSystemDirective,
@@ -45,6 +45,12 @@ export function createKeywordDetectorHook(ctx: PluginInput, _collector?: Context
 
       const currentAgent = getSessionAgent(input.sessionID) ?? input.agent
 
+      // Skip all keyword injection for non-OMO agents (e.g., OpenCode-Builder, Plan)
+      if (isNonOmoAgent(currentAgent)) {
+        log(`[keyword-detector] Skipping keyword injection for non-OMO agent`, { sessionID: input.sessionID, agent: currentAgent })
+        return
+      }
+
       // Remove system-reminder content to prevent automated system messages from triggering mode keywords
       const cleanText = removeSystemReminders(promptText)
       const modelID = input.model?.modelID
diff --git a/src/hooks/keyword-detector/index.test.ts b/src/hooks/keyword-detector/index.test.ts
index bf162ddeb..083c6b4f3 100644
--- a/src/hooks/keyword-detector/index.test.ts
+++ b/src/hooks/keyword-detector/index.test.ts
@@ -746,3 +746,109 @@ describe("keyword-detector agent-specific ultrawork messages", () => {
     expect(textPart!.text).not.toContain("YOU ARE A PLANNER, NOT AN IMPLEMENTER")
   })
 })
+
+describe("keyword-detector non-OMO agent skipping", () => {
+  let logCalls: Array<{ msg: string; data?: unknown }>
+  let logSpy: ReturnType<typeof spyOn>
+
+  beforeEach(() => {
+    _resetForTesting()
+    logCalls = []
+    logSpy = spyOn(sharedModule, "log").mockImplementation((msg: string, data?: unknown) => {
+      logCalls.push({ msg, data })
+    })
+  })
+
+  afterEach(() => {
+    logSpy?.mockRestore()
+    _resetForTesting()
+  })
+
+  function createMockPluginInput() {
+    return {
+      client: {
+        tui: {
+          showToast: async () => {},
+        },
+      },
+    } as any
+  }
+
+  test("should skip all keyword injection for OpenCode-Builder agent", async () => {
+    // given - keyword-detector hook with Builder agent
+    const collector = new ContextCollector()
+    const hook = createKeywordDetectorHook(createMockPluginInput(), collector)
+    const sessionID = "builder-session"
+    const output = {
+      message: {} as Record<string, unknown>,
+      parts: [{ type: "text", text: "ultrawork search and analyze this code" }],
+    }
+
+    // when - keyword detection runs with OpenCode-Builder agent
+    await hook["chat.message"]({ sessionID, agent: "OpenCode-Builder" }, output)
+
+    // then - no keywords should be injected
+    const textPart = output.parts.find(p => p.type === "text")
+    expect(textPart).toBeDefined()
+    expect(textPart!.text).toBe("ultrawork search and analyze this code")
+  })
+
+  test("should skip all keyword injection for Plan agent", async () => {
+    // given - keyword-detector hook with Plan agent
+    const collector = new ContextCollector()
+    const hook = createKeywordDetectorHook(createMockPluginInput(), collector)
+    const sessionID = "plan-session"
+    const output = {
+      message: {} as Record<string, unknown>,
+      parts: [{ type: "text", text: "search mode analyze mode ultrawork" }],
+    }
+
+    // when - keyword detection runs with Plan agent
+    await hook["chat.message"]({ sessionID, agent: "Plan" }, output)
+
+    // then - no keywords should be injected for non-OMO Plan agent
+    const textPart = output.parts.find(p => p.type === "text")
+    expect(textPart).toBeDefined()
+    expect(textPart!.text).toBe("search mode analyze mode ultrawork")
+  })
+
+  test("should still inject keywords for OMO agents like Sisyphus", async () => {
+    // given - keyword-detector hook with Sisyphus agent
+    const collector = new ContextCollector()
+    const hook = createKeywordDetectorHook(createMockPluginInput(), collector)
+    const sessionID = "sisyphus-session-omo"
+    const output = {
+      message: {} as Record<string, unknown>,
+      parts: [{ type: "text", text: "ultrawork implement this" }],
+    }
+
+    // when - keyword detection runs with Sisyphus (OMO agent)
+    await hook["chat.message"]({ sessionID, agent: "sisyphus" }, output)
+
+    // then - keywords should be injected normally
+    const textPart = output.parts.find(p => p.type === "text")
+    expect(textPart).toBeDefined()
+    expect(textPart!.text).toContain("YOU MUST LEVERAGE ALL AVAILABLE AGENTS")
+    expect(textPart!.text).toContain("implement this")
+  })
+
+  test("should skip keyword injection for agent names containing 'builder'", async () => {
+    // given - keyword-detector hook with a builder-variant agent name
+    const collector = new ContextCollector()
+    const hook = createKeywordDetectorHook(createMockPluginInput(), collector)
+    const sessionID = "custom-builder-session"
+    const output = {
+      message: {} as Record<string, unknown>,
+      parts: [{ type: "text", text: "search this codebase" }],
+    }
+
+    // when - keyword detection runs with a builder-type agent
+    await hook["chat.message"]({ sessionID, agent: "Custom-Builder" }, output)
+
+    // then - search-mode should NOT be injected
+    const textPart = output.parts.find(p => p.type === "text")
+    expect(textPart).toBeDefined()
+    expect(textPart!.text).toBe("search this codebase")
+    expect(textPart!.text).not.toContain("[search-mode]")
+  })
+})
diff --git a/src/hooks/keyword-detector/ultrawork/index.ts b/src/hooks/keyword-detector/ultrawork/index.ts
index f0f208fb3..3b732cafe 100644
--- a/src/hooks/keyword-detector/ultrawork/index.ts
+++ b/src/hooks/keyword-detector/ultrawork/index.ts
@@ -10,6 +10,7 @@
 
 export {
   isPlannerAgent,
+  isNonOmoAgent,
   isGptModel,
   isGeminiModel,
   getUltraworkSource,
diff --git a/src/hooks/keyword-detector/ultrawork/source-detector.ts b/src/hooks/keyword-detector/ultrawork/source-detector.ts
index ad1ff4755..2ee01a6de 100644
--- a/src/hooks/keyword-detector/ultrawork/source-detector.ts
+++ b/src/hooks/keyword-detector/ultrawork/source-detector.ts
@@ -23,6 +23,16 @@ export function isPlannerAgent(agentName?: string): boolean {
   return /\bplan\b/.test(normalized)
 }
 
+/**
+ * Checks if agent is a non-OMO agent (e.g., OpenCode's built-in Builder/Plan).
+ * Non-OMO agents should not receive keyword injection (search-mode, analyze-mode, etc.).
+ */
+export function isNonOmoAgent(agentName?: string): boolean {
+  if (!agentName) return false
+  const lowerName = agentName.toLowerCase()
+  return lowerName.includes("builder") || lowerName === "plan"
+}
+
 export { isGptModel, isGeminiModel }
 
 /** Ultrawork message source type */