diff --git a/src/create-prompt/index.ts b/src/create-prompt/index.ts
index d498cf9..27574d6 100644
--- a/src/create-prompt/index.ts
+++ b/src/create-prompt/index.ts
@@ -242,7 +242,7 @@ export function prepareContext(
       }
 
       if (eventAction === "assigned") {
-        if (!assigneeTrigger) {
+        if (!assigneeTrigger && !directPrompt) {
           throw new Error(
             "ASSIGNEE_TRIGGER is required for issue assigned event",
           );
@@ -254,7 +254,7 @@ export function prepareContext(
           issueNumber,
           baseBranch,
           claudeBranch,
-          assigneeTrigger,
+          ...(assigneeTrigger && { assigneeTrigger }),
         };
       } else if (eventAction === "opened") {
         eventData = {
@@ -331,7 +331,9 @@ export function getEventTypeAndContext(envVars: PreparedContext): {
       }
       return {
         eventType: "ISSUE_ASSIGNED",
-        triggerContext: `issue assigned to '${eventData.assigneeTrigger}'`,
+        triggerContext: eventData.assigneeTrigger
+          ? `issue assigned to '${eventData.assigneeTrigger}'`
+          : `issue assigned event`,
       };
 
     case "pull_request":
diff --git a/src/create-prompt/types.ts b/src/create-prompt/types.ts
index 00bba5e..4d83d97 100644
--- a/src/create-prompt/types.ts
+++ b/src/create-prompt/types.ts
@@ -65,7 +65,7 @@ type IssueAssignedEvent = {
   issueNumber: string;
   baseBranch: string;
   claudeBranch: string;
-  assigneeTrigger: string;
+  assigneeTrigger?: string;
 };
 
 type PullRequestEvent = {
diff --git a/test/create-prompt.test.ts b/test/create-prompt.test.ts
index 472ff65..b707b0f 100644
--- a/test/create-prompt.test.ts
+++ b/test/create-prompt.test.ts
@@ -614,6 +614,29 @@ describe("getEventTypeAndContext", () => {
     expect(result.eventType).toBe("ISSUE_ASSIGNED");
     expect(result.triggerContext).toBe("issue assigned to 'claude-bot'");
   });
+
+  test("should return correct type and context for issue assigned without assigneeTrigger", () => {
+    const envVars: PreparedContext = {
+      repository: "owner/repo",
+      claudeCommentId: "12345",
+      triggerPhrase: "@claude",
+      directPrompt: "Please assess this issue",
+      eventData: {
+        eventName: "issues",
+        eventAction: "assigned",
+        isPR: false,
+        issueNumber: "999",
+        baseBranch: "main",
+        claudeBranch: "claude/issue-999-20240101_120000",
+        // No assigneeTrigger when using directPrompt
+      },
+    };
+
+    const result = getEventTypeAndContext(envVars);
+
+    expect(result.eventType).toBe("ISSUE_ASSIGNED");
+    expect(result.triggerContext).toBe("issue assigned event");
+  });
 });
 
 describe("buildAllowedToolsString", () => {
diff --git a/test/prepare-context.test.ts b/test/prepare-context.test.ts
index 7811c5b..904dd37 100644
--- a/test/prepare-context.test.ts
+++ b/test/prepare-context.test.ts
@@ -219,6 +219,55 @@ describe("parseEnvVarsWithContext", () => {
         ),
       ).toThrow("BASE_BRANCH is required for issues event");
     });
+
+    test("should allow issue assigned event with direct_prompt and no assigneeTrigger", () => {
+      const contextWithDirectPrompt = createMockContext({
+        ...mockIssueAssignedContext,
+        inputs: {
+          ...mockIssueAssignedContext.inputs,
+          assigneeTrigger: "", // No assignee trigger
+          directPrompt: "Please assess this issue", // But direct prompt is provided
+        },
+      });
+
+      const result = prepareContext(
+        contextWithDirectPrompt,
+        "12345",
+        "main",
+        "claude/issue-123-20240101_120000",
+      );
+
+      expect(result.eventData.eventName).toBe("issues");
+      expect(result.eventData.isPR).toBe(false);
+      expect(result.directPrompt).toBe("Please assess this issue");
+      if (
+        result.eventData.eventName === "issues" &&
+        result.eventData.eventAction === "assigned"
+      ) {
+        expect(result.eventData.issueNumber).toBe("123");
+        expect(result.eventData.assigneeTrigger).toBeUndefined();
+      }
+    });
+
+    test("should throw error when neither assigneeTrigger nor directPrompt provided for issue assigned event", () => {
+      const contextWithoutTriggers = createMockContext({
+        ...mockIssueAssignedContext,
+        inputs: {
+          ...mockIssueAssignedContext.inputs,
+          assigneeTrigger: "", // No assignee trigger
+          directPrompt: "", // No direct prompt
+        },
+      });
+
+      expect(() =>
+        prepareContext(
+          contextWithoutTriggers,
+          "12345",
+          "main",
+          "claude/issue-123-20240101_120000",
+        ),
+      ).toThrow("ASSIGNEE_TRIGGER is required for issue assigned event");
+    });
   });
 
   describe("optional fields", () => {