diff --git a/AGENTS.md b/AGENTS.md
index f886ee72..9aae7e66 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -85,7 +85,7 @@ There is intentionally no after-agent safety net that opens a PR for the agent.
 All tools live in `agent/tools/` and are flat-imported via `agent/tools/__init__.py`. The set is intentionally small and curated — see README "Tools — Curated, Not Accumulated".
 
 Wired into `get_agent`:
-`http_request`, `fetch_url`, `web_search`, `linear_comment`, `linear_create_issue`, `linear_delete_issue`, `linear_get_issue`, `linear_get_issue_comments`, `linear_list_teams`, `linear_update_issue`, `request_pr_review`, `schedule_thread_wakeup`, `slack_read_thread_messages`, `slack_thread_reply`.
+`http_request`, `fetch_url`, `web_search`, `linear_comment`, `linear_create_issue`, `linear_delete_issue`, `linear_get_issue`, `linear_get_issue_comments`, `linear_list_teams`, `linear_update_issue`, `request_pr_review`, `schedule_thread_wakeup`, `slack_add_reaction`, `slack_read_thread_messages`, `slack_thread_reply`.
 
 Reviewer-only tools (in `agent/reviewer.py`): `add_finding`, `update_finding`, `list_findings`, `publish_review`. The review-style analyzer uses `save_review_style` (exported as `save_review_style_prompt`).
 
diff --git a/CLAUDE.md b/CLAUDE.md
index 2f41c049..2c35b827 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -81,7 +81,7 @@ There is intentionally no after-agent safety net that opens a PR for the agent.
 All tools live in `agent/tools/` and are flat-imported via `agent/tools/__init__.py`. The set is intentionally small and curated — see README "Tools — Curated, Not Accumulated".
 
 Wired into `get_agent`:
-`http_request`, `fetch_url`, `web_search`, `linear_comment`, `linear_create_issue`, `linear_delete_issue`, `linear_get_issue`, `linear_get_issue_comments`, `linear_list_teams`, `linear_update_issue`, `request_pr_review`, `schedule_thread_wakeup`, `slack_read_thread_messages`, `slack_thread_reply`.
+`http_request`, `fetch_url`, `web_search`, `linear_comment`, `linear_create_issue`, `linear_delete_issue`, `linear_get_issue`, `linear_get_issue_comments`, `linear_list_teams`, `linear_update_issue`, `request_pr_review`, `schedule_thread_wakeup`, `slack_add_reaction`, `slack_read_thread_messages`, `slack_thread_reply`.
 
 Reviewer-only tools (in `agent/reviewer.py`): `add_finding`, `update_finding`, `list_findings`, `publish_review`. The review-style analyzer uses `save_review_style` (exported as `save_review_style_prompt`).
 
diff --git a/README.md b/README.md
index 88b1058c..d3e666ca 100644
--- a/README.md
+++ b/README.md
@@ -72,6 +72,7 @@ Stripe's key insight: *tool curation matters more than tool quantity.* Open SWE
 | `fetch_url` | Fetch web pages as markdown |
 | `http_request` | API calls (GET, POST, etc.) |
 | `linear_comment` | Post updates to Linear tickets |
+| `slack_add_reaction` | React to Slack messages |
 | `slack_thread_reply` | Reply in Slack threads |
 
 GitHub operations are performed with `GH_TOKEN=dummy gh` inside the sandbox, backed by the LangSmith proxy. Plus the built-in Deep Agents tools: `read_file`, `write_file`, `edit_file`, `ls`, `glob`, `grep`, `write_todos`, and `task` (subagent spawning).
diff --git a/agent/middleware/refresh_slack_status.py b/agent/middleware/refresh_slack_status.py
index 6c52cc88..cfcf1dd0 100644
--- a/agent/middleware/refresh_slack_status.py
+++ b/agent/middleware/refresh_slack_status.py
@@ -55,6 +55,7 @@ _TOOL_STATUS: dict[str, str] = {
     "fetch_url": "fetching a URL...",
     "http_request": "making an HTTP request...",
     "request_pr_review": "requesting a PR review...",
+    "slack_add_reaction": "reacting in Slack...",
     "slack_read_thread_messages": "reading Slack history...",
     "slack_thread_reply": "drafting a Slack reply...",
     "linear_comment": "commenting on Linear...",
diff --git a/agent/prompt.py b/agent/prompt.py
index 7eea8341..83f3c2ea 100644
--- a/agent/prompt.py
+++ b/agent/prompt.py
@@ -84,6 +84,7 @@ OPEN_SWE_SHARED_BASE = """You are **Open SWE**, an open-source agent built on La
 
 - Focus on the substance and keep summaries brief. Use light markdown (`###`/`####` headings, bold, code) — avoid `#`/`##` titles.
 - In Slack, when a user asks to “break out,” “split out,” or “start a separate thread” for part of the work, summarize the requested aspect and relevant context into self-contained instructions, then call `slack_start_new_thread` instead of only replying in the current thread.
+- In Slack, when acknowledging a user follow-up while you continue working, prefer `slack_add_reaction` with the default `eyes` reaction over posting a perfunctory “Updating…” / “I’ll check…” confirmation reply.
 - When you post to Slack with `slack_thread_reply`, do not repeat that text in a later assistant message; the user can already see the Slack message.
 - When delegated work to a subagent: the calling agent only sees your final message, so make it the complete answer.
 
diff --git a/agent/server.py b/agent/server.py
index c16d36ab..bfdf485f 100644
--- a/agent/server.py
+++ b/agent/server.py
@@ -85,6 +85,7 @@ from .tools import (
     request_pr_review,
     save_plan,
     schedule_thread_wakeup,
+    slack_add_reaction,
     slack_read_thread_messages,
     slack_start_new_thread,
     slack_thread_reply,
@@ -959,6 +960,7 @@ async def get_agent(config: RunnableConfig) -> Pregel:
             open_pull_request,
             request_pr_review,
             schedule_thread_wakeup,
+            slack_add_reaction,
             slack_read_thread_messages,
             slack_start_new_thread,
             slack_thread_reply,
diff --git a/agent/tools/__init__.py b/agent/tools/__init__.py
index 532324d2..96aa85d0 100644
--- a/agent/tools/__init__.py
+++ b/agent/tools/__init__.py
@@ -20,6 +20,7 @@ from .resolve_finding_thread import resolve_finding_thread
 from .save_plan import save_plan
 from .schedule_thread_wakeup import schedule_thread_wakeup
 from .search_repo_code import search_repo_code
+from .slack_add_reaction import slack_add_reaction
 from .slack_read_thread_messages import slack_read_thread_messages
 from .slack_start_new_thread import slack_start_new_thread
 from .slack_thread_reply import slack_thread_reply
@@ -49,6 +50,7 @@ __all__ = [
     "save_plan",
     "schedule_thread_wakeup",
     "search_repo_code",
+    "slack_add_reaction",
     "slack_read_thread_messages",
     "slack_start_new_thread",
     "slack_thread_reply",
diff --git a/agent/tools/slack_add_reaction.py b/agent/tools/slack_add_reaction.py
new file mode 100644
index 00000000..b518c8bb
--- /dev/null
+++ b/agent/tools/slack_add_reaction.py
@@ -0,0 +1,46 @@
+from typing import Any
+
+from langgraph.config import get_config
+
+from ..utils.slack import add_slack_reaction
+
+
+async def slack_add_reaction(
+    emoji: str = "eyes",
+    message_ts: str | None = None,
+) -> dict[str, Any]:
+    """Add a reaction to a Slack message in the current Slack thread.
+
+    Use this with the default `eyes` reaction to acknowledge Slack user follow-up
+    requests while you continue working, instead of posting a perfunctory
+    confirmation reply. If `message_ts` is omitted, this reacts to the latest
+    message that triggered the run. Pass emoji names without surrounding colons.
+    """
+    config = get_config()
+    configurable = config.get("configurable", {})
+    slack_thread = configurable.get("slack_thread", {})
+
+    channel_id = slack_thread.get("channel_id")
+    if not channel_id:
+        return {"success": False, "error": "Missing slack_thread.channel_id in config"}
+
+    target_ts = (message_ts or slack_thread.get("triggering_event_ts") or "").strip()
+    if not target_ts:
+        return {
+            "success": False,
+            "error": "Missing message_ts and slack_thread.triggering_event_ts in config",
+        }
+
+    reaction = emoji.strip().strip(":")
+    if not reaction:
+        return {"success": False, "error": "emoji is required"}
+    if any(char.isspace() for char in reaction):
+        return {
+            "success": False,
+            "error": "emoji must be a Slack reaction name without whitespace",
+        }
+
+    success = await add_slack_reaction(channel_id, target_ts, reaction)
+    if not success:
+        return {"success": False, "error": "Could not add Slack reaction"}
+    return {"success": True}
diff --git a/agent/webhooks/slack.py b/agent/webhooks/slack.py
index 96b8e47f..45dfec65 100644
--- a/agent/webhooks/slack.py
+++ b/agent/webhooks/slack.py
@@ -142,8 +142,10 @@ async def process_slack_mention(event_data: dict[str, Any], repo_config: dict[st
         f"## Latest Mention Request\n{clean_text}\n\n"
         + (f"{resolved_links_section}\n\n" if resolved_links_section else "")
         + "Use `slack_thread_reply` to communicate in this Slack thread for clarifications, "
-        "status updates, and final summaries. Use `slack_read_thread_messages` to read any "
-        "Slack messages by providing channel_id and message_ts."
+        "substantive updates, and final summaries. Use `slack_add_reaction` with :eyes: "
+        "instead of posting perfunctory confirmation replies to user follow-up requests. "
+        "Use `slack_read_thread_messages` to read any Slack messages by providing channel_id "
+        "and message_ts."
     )
     content_blocks: list[dict[str, Any]] = [create_text_block(prompt)]
 
diff --git a/tests/test_slack_add_reaction_tool.py b/tests/test_slack_add_reaction_tool.py
new file mode 100644
index 00000000..41cd3855
--- /dev/null
+++ b/tests/test_slack_add_reaction_tool.py
@@ -0,0 +1,78 @@
+from __future__ import annotations
+
+import importlib
+from typing import Any
+
+import pytest
+
+slack_reaction_tool = importlib.import_module("agent.tools.slack_add_reaction")
+
+
+def _config() -> dict[str, Any]:
+    return {
+        "configurable": {
+            "slack_thread": {
+                "channel_id": "C1",
+                "thread_ts": "1.0",
+                "triggering_event_ts": "1.1",
+            }
+        }
+    }
+
+
+async def test_slack_add_reaction_defaults_to_triggering_event(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    captured: dict[str, str] = {}
+
+    async def fake_add_slack_reaction(
+        channel_id: str, message_ts: str, emoji: str = "eyes"
+    ) -> bool:
+        captured.update({"channel_id": channel_id, "message_ts": message_ts, "emoji": emoji})
+        return True
+
+    monkeypatch.setattr(slack_reaction_tool, "get_config", _config)
+    monkeypatch.setattr(slack_reaction_tool, "add_slack_reaction", fake_add_slack_reaction)
+
+    result = await slack_reaction_tool.slack_add_reaction()
+
+    assert result == {"success": True}
+    assert captured == {"channel_id": "C1", "message_ts": "1.1", "emoji": "eyes"}
+
+
+async def test_slack_add_reaction_accepts_explicit_message_and_normalizes_emoji(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    captured: dict[str, str] = {}
+
+    async def fake_add_slack_reaction(
+        channel_id: str, message_ts: str, emoji: str = "eyes"
+    ) -> bool:
+        captured.update({"channel_id": channel_id, "message_ts": message_ts, "emoji": emoji})
+        return True
+
+    monkeypatch.setattr(slack_reaction_tool, "get_config", _config)
+    monkeypatch.setattr(slack_reaction_tool, "add_slack_reaction", fake_add_slack_reaction)
+
+    result = await slack_reaction_tool.slack_add_reaction(
+        emoji=":white_check_mark:", message_ts="1.2"
+    )
+
+    assert result == {"success": True}
+    assert captured == {"channel_id": "C1", "message_ts": "1.2", "emoji": "white_check_mark"}
+
+
+async def test_slack_add_reaction_requires_slack_channel(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(slack_reaction_tool, "get_config", lambda: {"configurable": {}})
+
+    result = await slack_reaction_tool.slack_add_reaction()
+
+    assert result == {"success": False, "error": "Missing slack_thread.channel_id in config"}
+
+
+async def test_slack_add_reaction_rejects_empty_emoji(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(slack_reaction_tool, "get_config", _config)
+
+    result = await slack_reaction_tool.slack_add_reaction(emoji="::")
+
+    assert result == {"success": False, "error": "emoji is required"}