diff --git a/src/monitor_service/models.py b/src/monitor_service/models.py
new file mode 100644
index 0000000..84bd06b
--- /dev/null
+++ b/src/monitor_service/models.py
@@ -0,0 +1,58 @@
+from datetime import datetime, timezone
+from enum import Enum
+from uuid import UUID
+
+from pydantic import BaseModel, ConfigDict, Field, HttpUrl, model_validator
+
+
+def utc_now() -> datetime:
+    return datetime.now(timezone.utc)
+
+
+class MonitorState(str, Enum):
+    unknown = "unknown"
+    up = "up"
+    down = "down"
+
+
+class MonitorCreate(BaseModel):
+    name: str = Field(min_length=1, max_length=120)
+    url: HttpUrl
+
+
+class MonitorUpdate(BaseModel):
+    name: str | None = Field(default=None, min_length=1, max_length=120)
+    url: HttpUrl | None = None
+
+    @model_validator(mode="after")
+    def reject_nulls(self) -> "MonitorUpdate":
+        if any(value is None for value in self.model_dump(exclude_unset=True).values()):
+            raise ValueError("updated fields cannot be null")
+        return self
+
+
+class CurrentStatus(BaseModel):
+    model_config = ConfigDict(frozen=True)
+
+    state: MonitorState = MonitorState.unknown
+    checked_at: datetime | None = None
+    latency_ms: float | None = None
+    http_status: int | None = None
+    error: str | None = None
+
+
+class Monitor(BaseModel):
+    model_config = ConfigDict(frozen=True)
+
+    id: UUID
+    name: str
+    url: HttpUrl
+    created_at: datetime
+    updated_at: datetime
+    status: CurrentStatus
+
+
+class CheckResult(BaseModel):
+    monitor_id: UUID
+    url: str
+    status: CurrentStatus