diff --git a/app/models.py b/app/models.py
index 3d2910a..237a4ea 100644
--- a/app/models.py
+++ b/app/models.py
@@ -1,51 +1,65 @@
-from datetime import datetime
-from typing import Literal
+from datetime import datetime, timezone
+from enum import Enum
+from typing import Annotated
 from uuid import UUID
 
-from pydantic import AnyHttpUrl, BaseModel, ConfigDict, Field, model_validator
+from pydantic import AnyHttpUrl, BaseModel, ConfigDict, Field, StringConstraints, field_validator
 
-StatusState = Literal["unknown", "up", "down", "error"]
+Name = Annotated[str, StringConstraints(strip_whitespace=True, min_length=1, max_length=100)]
 
 
-class CheckStatus(BaseModel):
-    state: StatusState = "unknown"
-    checked_at: datetime | None = None
-    status_code: int | None = None
-    latency_ms: float | None = Field(default=None, ge=0)
-    error: str | None = None
+def utcnow() -> datetime:
+    return datetime.now(timezone.utc)
+
+
+class MonitorStatus(str, Enum):
+    unknown = "unknown"
+    up = "up"
+    down = "down"
+    error = "error"
 
 
 class MonitorCreate(BaseModel):
-    name: str = Field(min_length=1, max_length=200)
+    name: Name
     url: AnyHttpUrl
 
+    @field_validator("url")
+    @classmethod
+    def no_credentials(cls, value: AnyHttpUrl) -> AnyHttpUrl:
+        if value.username or value.password:
+            raise ValueError("URL credentials are not allowed")
+        return value
 
-class MonitorUpdate(BaseModel):
-    name: str | None = Field(default=None, min_length=1, max_length=200)
-    url: AnyHttpUrl | None = None
 
-    @model_validator(mode="after")
-    def not_empty(self) -> "MonitorUpdate":
-        if self.name is None and self.url is None:
-            raise ValueError("at least one field is required")
-        return self
+class MonitorUpdate(MonitorCreate):
+    pass
 
 
 class Monitor(BaseModel):
-    model_config = ConfigDict(from_attributes=True)
-
+    model_config = ConfigDict(frozen=True)
     id: UUID
     name: str
     url: AnyHttpUrl
+    status: MonitorStatus = MonitorStatus.unknown
     created_at: datetime
     updated_at: datetime
-    status: CheckStatus
+    checked_at: datetime | None = None
+    latency_ms: float | None = Field(default=None, ge=0)
+    http_status: int | None = Field(default=None, ge=100, le=599)
+    error: str | None = None
 
 
-class CheckResult(CheckStatus):
-    monitor_id: UUID
-    status_applied: bool = True
+class CheckResult(BaseModel):
+    status: MonitorStatus
+    checked_at: datetime
+    latency_ms: float = Field(ge=0)
+    http_status: int | None = None
+    error: str | None = None
 
 
-class HealthResponse(BaseModel):
-    status: Literal["ok", "ready"]
+class StatusResponse(CheckResult):
+    id: UUID
+
+
+class ProbeResponse(BaseModel):
+    status: str