Every time a PyTorch model refuses to learn, the debugging process looks the same:
- Stare at the loss curve
- Wonder if gradients are flowing
- Add print statements everywhere
- Delete them all when it works
- Repeat next week
After 17 years in distributed systems and SRE, I know this pattern — it is monitoring by vibes. In production infrastructure, we would never accept "the service seems slow" as a diagnostic. We measure. We trace. We verify.
So I built torchdiag — five diagnostic commands that answer the actual questions.
Install
pip install torchdiag
AddyM
/
torchdiag
PyTorch model health diagnostics — gradient checks, dead neuron detection, training verification. Built from an SRE perspective.
torchdiag
PyTorch model health diagnostics — built from an SRE perspective.
Stop guessing why your model isn't learning. torchdiag gives you five diagnostic commands that answer the questions that matter: Are gradients flowing? Are neurons alive? Did the optimizer actually update weights?
Installation
pip install torchdiag
Quick Start
import torch import torch.nn as nn import torchdiag model = nn.Sequential( nn.Linear(784, 256), nn.ReLU(), nn.Linear(256, 64), nn.ReLU(), nn.Linear(64, 10), ) # 1. Model overview torchdiag.summary(model) # 2. Check for dead neurons x = torch.randn(100, 784) torchdiag.check_dead_neurons(model, x) # 3. Verify a full training step works torchdiag.verify_step( model, torch.optim.Adam
…
1. What does my model actually look like?
import torchdiag
import torch.nn as nn
model = nn.Sequential(
nn.Linear(784, 256),
nn.ReLU(),
nn.Linear(256, 64),
nn.ReLU(),
nn.Linear(64, 10),
)
torchdiag.summary(model)
Prints parameter count per layer, total/trainable/frozen breakdown, memory footprint, device placement, and dtype distribution. Flags frozen parameters, split-device models, and dtype mismatches.
2. Are gradients flowing?
loss = nn.CrossEntropyLoss()(model(x), target)
loss.backward()
torchdiag.check_gradients(model)
Reports gradient mean, max, and min per layer. Flags vanishing gradients (max below 1e-7), exploding gradients (max above 100), and disconnected parameters (None gradients).
3. Are neurons alive?
x = torch.randn(100, 784)
torchdiag.check_dead_neurons(model, x)
A dead ReLU neuron outputs zero for every input. Its gradient is permanently zero. It will never learn again. This command tells you how many you have and where. Flags critical layers with more than 50% dead neurons.
4. Does one training step actually work?
torchdiag.verify_step(
model,
torch.optim.Adam(model.parameters()),
nn.CrossEntropyLoss(),
torch.randn(32, 784),
torch.randint(0, 10, (32,)),
)
Runs one complete training step — forward, loss, backward, optimizer step — and verifies each stage works. Confirms output shape is correct, loss is finite, gradients are computed, and parameters actually change.
Run this before your training loop. If something is broken, you will know in 1 step instead of 100 epochs.
5. How much memory am I using?
torchdiag.memory_report()
Reports CPU RSS, GPU allocated/cached/peak per device, and MPS memory on Apple Silicon. Flags when GPU utilization exceeds 90%.
Why I Built This
I spent 11 years at VMware working on distributed systems observability. The first thing you learn in SRE: never trust a system you cannot measure.
PyTorch models are systems. They have inputs, internal state, and outputs. When they fail, they fail silently — the loss just stays flat. No error. No exception. Just a number that does not move.
torchdiag makes the internal state visible. Five commands. No configuration. No dependencies beyond PyTorch.
PyPI: pypi.org/project/torchdiag
GitHub: github.com/AddyM/torchdiag
CI: Tests pass across Python 3.9 to 3.12
Contributions welcome. If you have a debugging pattern you use repeatedly, open an issue — it probably belongs in the toolkit.