> ## Documentation Index > Fetch the complete documentation index at: https://site.aspect.build/llms.txt > Use this file to discover all available pages before exploring further. # error `function` **error.type** 
        
          def error.type(
          \*,
          fields: dict\[str, typing.Any] = ...,
          traceback: None | bool = None
          ) -> error\_type
Derive a new error type from this one. The new type inherits every field of this type and adds `fields`. Its instances are also instances of this type and of each of its ancestors, for both `isinstance` and type annotations. The name comes from the variable the type is first assigned to, so declare error types at module top level. `fields` maps each field name to a type, or to `attr(type, default = ...)` for an optional field, as `trait()` does. `message`, `stacktrace` and `cause` are reserved, and an inherited field cannot be redeclared. `traceback` decides how an error of this type renders when it escapes the task. `True` shows the traceback, as for a bug. `False` prints the message alone as an `ERROR:` line and exits with code 1, as `ctx.std.process.exit` does: use it for expected refusals. Unset, it is inherited; the root `error` has `True`. ```starlark theme={null} DeployError = error.type(fields = {"deployment": str, "attempt": attr(int, default = 1)}) DeployTimeout = DeployError.type(fields = {"after_ms": int}) NotLoggedIn = error.type(traceback = False) ``` `property` **error.cause** 
        
          error.cause: typing.Any
The error that led to this one, or `None`. `property` **error.message** 
        
          error.message: str
What went wrong, as given to the constructor. `str(e)` returns it too. `property` **error.stacktrace** 
        
          error.stacktrace: typing.Any
Where the error was constructed, as a list of frames, outermost call first. For an error the runtime built from a failed operation, it is where that failure reached AXL, e.g. the `future.block()` call.