diff --git a/quantboard/ui/state.py b/quantboard/ui/state.py
new file mode 100644
index 0000000..51dc1fa
--- /dev/null
+++ b/quantboard/ui/state.py
@@ -0,0 +1,104 @@
+"""Utilities for synchronizing URL query params with Streamlit session state."""
+
+from typing import Any, Dict
+
+import streamlit as st
+
+
+def _coerce_type(value: Any, default: Any) -> Any:
+    """Cast value to the type of default, falling back to default on failure."""
+    if value is None:
+        return default
+
+    target_type = type(default)
+
+    if isinstance(value, list):
+        if not value:
+            return default
+        value = value[0]
+
+    if target_type is type(None):
+        return None
+
+    if isinstance(value, target_type):
+        return value
+
+    try:
+        if target_type is bool:
+            if isinstance(value, str):
+                lowered = value.strip().lower()
+                if lowered in {"true", "1", "yes", "y", "on", "t"}:
+                    return True
+                if lowered in {"false", "0", "no", "n", "off", "f"}:
+                    return False
+            return bool(value)
+
+        return target_type(value)
+    except Exception:
+        return default
+
+
+def _get_query_params() -> Dict[str, Any]:
+    """Return query params supporting both the new and experimental Streamlit APIs."""
+    try:
+        params = st.query_params
+        if callable(getattr(params, "to_dict", None)):
+            params = params.to_dict()
+        else:
+            params = dict(params)
+        return {k: v for k, v in params.items()}
+    except Exception:
+        pass
+
+    try:
+        return st.experimental_get_query_params()
+    except Exception:
+        return {}
+
+
+def _set_query_params(params: Dict[str, Any]) -> None:
+    """Merge and set query params across the available Streamlit APIs."""
+    current = _get_query_params()
+    merged = {**current, **params}
+
+    def _normalize(value: Any) -> Any:
+        if isinstance(value, list):
+            return [str(v) for v in value]
+        if value is None:
+            return ""
+        return str(value)
+
+    normalized = {k: _normalize(v) for k, v in merged.items()}
+
+    try:
+        st.query_params = normalized
+        return
+    except Exception:
+        pass
+
+    try:
+        st.experimental_set_query_params(**normalized)
+    except Exception:
+        return
+
+
+def get_param(key: str, default: Any) -> Any:
+    """Fetch a parameter from the URL, falling back to session state or default."""
+    params = _get_query_params()
+    value = params.get(key)
+
+    if value is None:
+        if key in st.session_state:
+            value = st.session_state[key]
+        else:
+            value = default
+
+    coerced = _coerce_type(value, default)
+    st.session_state[key] = coerced
+    return coerced
+
+
+def set_param(key: str, value: Any) -> None:
+    """Update a parameter in session state and the URL query string."""
+    st.session_state[key] = value
+    _set_query_params({key: value})