diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 2b1908c..e25fb45 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -23,10 +23,12 @@ jobs:
     - name: Get code size
     - name: Train MNIST
       run: PYTHONPATH="." python mnist.py
-    - name: Install torch for testing
-      run: pip install torch --extra-index-url https://download.pytorch.org/whl/cpu
+    - name: Install mypy + torch for testing
+      run: pip install mypy torch --extra-index-url https://download.pytorch.org/whl/cpu
     - name: Test ops / dtype / optim
       run: |
        PYTHONPATH="." python test/test_ops.py
        PYTHONPATH="." python test/test_dtype.py
        PYTHONPATH="." python test/test_optim.py
+    - name: Check types with mypy
+      run: mypy
\ No newline at end of file
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
new file mode 100644
index 0000000..10d1df0
--- /dev/null
+++ b/.pre-commit-config.yaml
@@ -0,0 +1,15 @@
+repos:
+  - repo: local
+    hooks:
+      - id: tests
+        name: tests
+        entry: env PYTHONPATH="." pytest test/
+        language: system
+        always_run: true
+        pass_filenames: false
+      - id: mypy
+        name: mypy
+        entry: mypy
+        language: system
+        always_run: true
+        pass_filenames: false
\ No newline at end of file
diff --git a/mypy.ini b/mypy.ini
new file mode 100644
index 0000000..4e3c031
--- /dev/null
+++ b/mypy.ini
@@ -0,0 +1,9 @@
+[mypy]
+warn_unused_configs = True
+files = teenygrad
+ignore_missing_imports = True
+check_untyped_defs = True
+explicit_package_bases = True
+warn_unreachable = True
+warn_redundant_casts = True
+warn_unused_ignores = True
\ No newline at end of file
diff --git a/teenygrad/helpers.py b/teenygrad/helpers.py
index e11d219..7ad89af 100644
--- a/teenygrad/helpers.py
+++ b/teenygrad/helpers.py
@@ -10,7 +10,7 @@ def argfix(*x): return tuple(x[0]) if x and x[0].__class__ in (tuple, list) else
 def make_pair(x:Union[int, Tuple[int, ...]], cnt=2) -> Tuple[int, ...]: return (x,)*cnt if isinstance(x, int) else x
 def flatten(l:Iterator): return [item for sublist in l for item in sublist]
 def argsort(x): return type(x)(sorted(range(len(x)), key=x.__getitem__)) # https://stackoverflow.com/questions/3382352/equivalent-of-numpy-argsort-in-basic-python
-def all_int(t: Tuple[Any, ...]) -> Tuple[int, ...]: return all(isinstance(s, int) for s in t)
+def all_int(t: Tuple[Any, ...]) -> bool: return all(isinstance(s, int) for s in t)
 def round_up(num, amt:int): return (num+amt-1)//amt * amt
 
 @functools.lru_cache(maxsize=None)
diff --git a/teenygrad/lazy.py b/teenygrad/lazy.py
index 84cc4e6..41ee96e 100644
--- a/teenygrad/lazy.py
+++ b/teenygrad/lazy.py
@@ -12,6 +12,8 @@ class LazyBuffer:
 
   def __init__(self, buf: np.ndarray): self._np = buf
 
+  @property
+  def base(self): return self
   @property
   def dtype(self): return dtypes.from_np(self._np.dtype)
   @property
@@ -21,7 +23,8 @@ def shape(self): return self._np.shape
   def __repr__(self): return f"<LB {self.shape} {self.dtype}>"
 
   def schedule(self, seen=None): return []
-  def is_unrealized_const(self): return False
+  def is_unrealized_contiguous_const(self): return False
+  def copy_to_device(self, device:str) -> LazyBuffer: return self
 
   @staticmethod
   def fromCPU(x): return LazyBuffer(x)
diff --git a/teenygrad/ops.py b/teenygrad/ops.py
index 308d966..e72c98a 100644
--- a/teenygrad/ops.py
+++ b/teenygrad/ops.py
@@ -1,4 +1,5 @@
 from enum import Enum, auto
+from typing import Optional
 
 class UnaryOps(Enum): NOOP = auto(); EXP2 = auto(); LOG2 = auto(); CAST = auto(); SIN = auto(); SQRT = auto(); RECIP = auto(); NEG = auto() # noqa: E702
 class BinaryOps(Enum): ADD = auto(); SUB = auto(); MUL = auto(); DIV = auto(); MAX = auto(); MOD = auto(); CMPLT = auto() # noqa: E702
@@ -10,4 +11,5 @@ class LoadOps(Enum): EMPTY = auto(); RAND = auto(); CONST = auto(); FROM = auto(
 class Device:
   DEFAULT = "CPU"
   _buffers = ["CPU"]
-  def canonicalize(x): return "CPU"
+  @staticmethod
+  def canonicalize(device:Optional[str]) -> str: return "CPU"
diff --git a/teenygrad/tensor.py b/teenygrad/tensor.py
index 1d147ac..190e862 100644
--- a/teenygrad/tensor.py
+++ b/teenygrad/tensor.py
@@ -71,9 +71,9 @@ def __init__(self, data:Union[None, int, float, list, LazyBuffer, np.ndarray, by
         data = LazyBuffer.loadop(LoadOps.CONST, tuple(), dtype or dtypes.from_np(data.dtype), device, data.item())
       else:
         data = LazyBuffer.fromCPU(data.astype(dtype.np) if dtype is not None and dtype.np is not None else data)
-    else: raise RuntimeError(f"can't create Tensor from {data} with type {type(data)}")
 
     # data is a LazyBuffer, but it might be on the wrong device
+    if not isinstance(data, LazyBuffer): raise RuntimeError(f"can't create Tensor from {data!r} with type {type(data)}")
     self.lazydata = data if data.device == device else data.copy_to_device(device)
 
   def __repr__(self):
@@ -673,8 +673,8 @@ def _broadcasted(self, y:Union[Tensor, float], reverse:bool=False) -> Tuple[Tens
     return (x, y)
 
   def _to_float(self, x:Union[Tensor, float]):
-    return x.lazydata.base.op.arg if isinstance(x, Tensor) and x.lazydata.is_unrealized_const() and not x.requires_grad \
-      and x.lazydata.st.contiguous and self._broadcasted(x)[0].shape == self.shape else x
+    return x.lazydata.base.op.arg if isinstance(x, Tensor) and x.lazydata.is_unrealized_contiguous_const() \
+      and not x.requires_grad and self._broadcasted(x)[0].shape == self.shape else x
 
   def add(self, x:Union[Tensor, float], reverse=False) -> Tensor:
     x = self._to_float(x)