diff --git a/tools.py b/tools.py
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--- /dev/null
+++ b/tools.py
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+"""
+Utility module that defines the tool(s) used by the streaming agent.
+
+The project currently contains a single mock ``get_price`` function.  The
+implementation is intentionally tiny – it simply looks up a hard‑coded price
+in a dictionary.  In real projects this would be replaced with an API call or
+database query.
+"""
+
+from langchain.tools import tool
+
+@tool
+def get_price(product: str, city: str) -> str:
+    """Return a fake price for *product* in *city*.
+
+    Parameters
+    ----------
+    product : str
+        Name of the product (e.g. ``milk``).
+    city : str
+        City where the price is requested.
+
+    Returns
+    -------
+    str
+        A string describing the price, e.g. ``"89 rubles"``.
+    """
+    prices = {
+        ("milk", "kazan"): "89",
+        ("bread", "kazan"): "45",
+        ("coffee", "moscow"): "120",
+    }
+    key = (product.lower(), city.lower())
+    price = prices.get(key, "unknown")
+    return f"{price} rubles"
+
+# End of tools.py