diff --git a/.env.example b/.env.example
index 262d3ba..fffb471 100644
--- a/.env.example
+++ b/.env.example
@@ -12,3 +12,8 @@ DAILY_CALL_LIMIT=50
 
 # Production frontend origin for CORS (e.g. https://your-app.railway.app)
 # ALLOWED_ORIGIN=https://your-app.railway.app
+
+# Sentry DSN for production error monitoring — optional, get one free at
+# https://sentry.io. Leave unset to disable error monitoring entirely (safe
+# default for local dev/CI).
+# SENTRY_DSN=https://...@o0.ingest.sentry.io/0
diff --git a/agent/main.py b/agent/main.py
index 8415923..423a0b8 100644
--- a/agent/main.py
+++ b/agent/main.py
@@ -5,6 +5,7 @@
 from datetime import date
 
 import anthropic
+import sentry_sdk
 from dotenv import load_dotenv
 
 from agent import db
@@ -249,6 +250,7 @@ def _run_tools(response_content: list, user_id: int, on_result=None, source: str
                 result = TOOL_HANDLERS[block.name](**kwargs)
             except Exception:
                 logger.error("tool %s(%s) failed:\n%s", block.name, kwargs, traceback.format_exc())
+                sentry_sdk.capture_exception()
                 result = {"status": "error", "message": f"{block.name} failed unexpectedly — tell the user and don't retry automatically."}
             db.record_usage(user_id, "tool", block.name, source)
             print(f"[tool] {block.name}({kwargs}) -> {result}")
diff --git a/api/server.py b/api/server.py
index 23188aa..0b69620 100644
--- a/api/server.py
+++ b/api/server.py
@@ -7,6 +7,7 @@
 from datetime import date
 from pathlib import Path
 
+import sentry_sdk
 from fastapi import Depends, FastAPI, HTTPException
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import FileResponse, StreamingResponse
@@ -37,6 +38,16 @@
 
 logger = logging.getLogger(__name__)
 
+# Error monitoring — a no-op until SENTRY_DSN is set (sentry_sdk.init(dsn=None)
+# disables the SDK entirely, so this is safe to leave unconfigured in dev/CI).
+# Error capture only, no performance tracing — that's a separate cost/scope
+# this app doesn't need yet. send_default_pii is explicitly off: the SDK
+# auto-instruments the anthropic client, and every Claude call here carries
+# real expense/income descriptions — that must never leave this app for a
+# third party, on top of the SYSTEM prompt/user messages being sensitive on
+# their own.
+sentry_sdk.init(dsn=os.environ.get("SENTRY_DSN"), traces_sample_rate=0.0, send_default_pii=False)
+
 DAILY_CALL_LIMIT = int(os.environ.get("DAILY_CALL_LIMIT", 50))
 
 
@@ -110,6 +121,7 @@ def generate():
                 yield f"data: {json.dumps(event)}\n\n"
         except Exception:
             logger.error("stream_chat error:\n%s", traceback.format_exc())
+            sentry_sdk.capture_exception()
             yield f"data: {json.dumps({'error': 'Something went wrong. Please try again.'})}\n\n"
         yield "data: [DONE]\n\n"
 
diff --git a/pyproject.toml b/pyproject.toml
index a4b00d1..6a8f3bf 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -10,6 +10,7 @@ dependencies = [
     "psycopg2-binary>=2.9.12",
     "python-dotenv>=1.2.2",
     "python-jose[cryptography]>=3.5.0",
+    "sentry-sdk>=2.65.0",
     "uvicorn>=0.49.0",
 ]
 
diff --git a/tests/test_agent.py b/tests/test_agent.py
index f8efaf4..7e60f59 100644
--- a/tests/test_agent.py
+++ b/tests/test_agent.py
@@ -125,6 +125,21 @@ def failing_handler(**kw):
     assert results[2]["content"] == str({"ok": True})
 
 
+def test_run_tools_reports_failing_handler_to_sentry(monkeypatch):
+    captured = []
+    monkeypatch.setattr(main.sentry_sdk, "capture_exception", lambda: captured.append(True))
+
+    def failing_handler(**kw):
+        raise ValueError("boom")
+
+    monkeypatch.setitem(main.TOOL_HANDLERS, "save_expense", failing_handler)
+    block = make_block("tool_use", name="save_expense", input={"amount": 5}, id="tool_1")
+
+    main._run_tools([block], user_id=1)
+
+    assert captured == [True]
+
+
 # --- _serialize_block --------------------------------------------------------
 # Required for persisting assistant turns to Postgres — a live Anthropic SDK
 # response block in production, but test doubles are plain dicts or
diff --git a/tests/test_api.py b/tests/test_api.py
index d273695..e64991c 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -302,6 +302,21 @@ def fake_stream_chat(message, user_id, username, images, source):
     assert "data: [DONE]" in response.text
 
 
+def test_chat_stream_endpoint_reports_exception_to_sentry(monkeypatch, auth_headers):
+    captured = []
+    monkeypatch.setattr(server.sentry_sdk, "capture_exception", lambda: captured.append(True))
+
+    def fake_stream_chat(message, user_id, username, images):
+        raise RuntimeError("boom")
+        yield  # pragma: no cover — makes this a generator, never reached
+
+    monkeypatch.setattr(server, "stream_chat", fake_stream_chat)
+
+    client.post("/chat/stream", json={"message": "hi"}, headers=auth_headers)
+
+    assert captured == [True]
+
+
 # --- check_rate_limit --------------------------------------------------
 
 def test_check_rate_limit_allows_calls_under_limit(user_id):
diff --git a/uv.lock b/uv.lock
index a379ccc..8bba098 100644
--- a/uv.lock
+++ b/uv.lock
@@ -295,6 +295,7 @@ dependencies = [
     { name = "psycopg2-binary" },
     { name = "python-dotenv" },
     { name = "python-jose", extra = ["cryptography"] },
+    { name = "sentry-sdk" },
     { name = "uvicorn" },
 ]
 
@@ -313,6 +314,7 @@ requires-dist = [
     { name = "psycopg2-binary", specifier = ">=2.9.12" },
     { name = "python-dotenv", specifier = ">=1.2.2" },
     { name = "python-jose", extras = ["cryptography"], specifier = ">=3.5.0" },
+    { name = "sentry-sdk", specifier = ">=2.65.0" },
     { name = "uvicorn", specifier = ">=0.49.0" },
 ]
 
@@ -644,6 +646,19 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/29/4c/67bb45e41609eb4726f1bfeb59e083cf91d14c696d4bd14c234a980be93d/ruff-0.15.18-py3-none-win_arm64.whl", hash = "sha256:b2c9257fcbd4a3e5b977a1904e6facca016bafe2edc17df24db67cfaee03b4e4", size = 11329958, upload-time = "2026-06-18T18:25:43.686Z" },
 ]
 
+[[package]]
+name = "sentry-sdk"
+version = "2.65.0"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "certifi" },
+    { name = "urllib3" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/f1/1f/ed17a390348156ca99fe622b97cd7d2f1969b5f49df89084b0f28e7953e9/sentry_sdk-2.65.0.tar.gz", hash = "sha256:c94dc945d54bad49d4f20448b1e6b217ca2f92f46d05c3e83d41764af685c3d1", size = 932133, upload-time = "2026-07-13T11:33:19.92Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/21/3b/326ad4c03b5da89b5124c8890af66e8119c4d2e10abc0619e0d67d9f7c7f/sentry_sdk-2.65.0-py3-none-any.whl", hash = "sha256:3595169677a808e4d0e1ea6ffb89443459549c7a98392ed71c77c847182ab6bf", size = 503869, upload-time = "2026-07-13T11:33:17.71Z" },
+]
+
 [[package]]
 name = "six"
 version = "1.17.0"
@@ -695,6 +710,15 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/dc/9b/47798a6c91d8bdb567fe2698fe81e0c6b7cb7ef4d13da4114b41d239f65d/typing_inspection-0.4.2-py3-none-any.whl", hash = "sha256:4ed1cacbdc298c220f1bd249ed5287caa16f34d44ef4e9c3d0cbad5b521545e7", size = 14611, upload-time = "2025-10-01T02:14:40.154Z" },
 ]
 
+[[package]]
+name = "urllib3"
+version = "2.7.0"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/53/0c/06f8b233b8fd13b9e5ee11424ef85419ba0d8ba0b3138bf360be2ff56953/urllib3-2.7.0.tar.gz", hash = "sha256:231e0ec3b63ceb14667c67be60f2f2c40a518cb38b03af60abc813da26505f4c", size = 433602, upload-time = "2026-05-07T16:13:18.596Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/7f/3e/5db95bcf282c52709639744ca2a8b149baccf648e39c8cc87553df9eae0c/urllib3-2.7.0-py3-none-any.whl", hash = "sha256:9fb4c81ebbb1ce9531cce37674bbc6f1360472bc18ca9a553ede278ef7276897", size = 131087, upload-time = "2026-05-07T16:13:17.151Z" },
+]
+
 [[package]]
 name = "uvicorn"
 version = "0.49.0"