diff --git a/src/agents/system-prompt.test.ts b/src/agents/system-prompt.test.ts
index 3877f6fed21..14a409e88a2 100644
--- a/src/agents/system-prompt.test.ts
+++ b/src/agents/system-prompt.test.ts
@@ -554,6 +554,7 @@ describe("buildAgentSystemPrompt", () => {
 
     expect(prompt).toContain("message: Send messages and channel actions");
     expect(prompt).toContain("### message tool");
+    expect(prompt).toContain("For `action=send`, include `target` and `message`.");
     expect(prompt).toContain(`respond with ONLY: ${SILENT_REPLY_TOKEN}`);
   });
 
diff --git a/src/agents/system-prompt.ts b/src/agents/system-prompt.ts
index 848222b7880..94d859f4e92 100644
--- a/src/agents/system-prompt.ts
+++ b/src/agents/system-prompt.ts
@@ -140,7 +140,7 @@ function buildMessagingSection(params: {
           "",
           "### message tool",
           "- Use `message` for proactive sends + channel actions (polls, reactions, etc.).",
-          "- For `action=send`, include `to` and `message`.",
+          "- For `action=send`, include `target` and `message`.",
           `- If multiple channels are configured, pass \`channel\` (${params.messageChannelOptions}).`,
           `- If you use \`message\` (\`action=send\`) to deliver your user-visible reply, respond with ONLY: ${SILENT_REPLY_TOKEN} (avoid duplicate replies).`,
           params.inlineButtonsEnabled