Free browser tool
NCCL log decoder
A watchdog timeout tells you a rank waited too long. It does not identify the rank that failed first. Check the preceding CUDA, host and transport messages across available rank logs before deciding what to investigate.
Try a synthetic sample below, then inspect your own logs in this browser. This decoder uses local pattern matching and does not send the text you paste to Denpex.
The sample is invented for demonstration. It is not a customer incident.
The decoder classifies covered signatures and marks timeout and launcher wrappers as secondary evidence. Logs stay in this browser.
What this decoder can establish
It recognizes a bounded set of literal signatures, extracts rank labels when present, and identifies the first non-wrapper finding by file order. It is useful for fast triage and for deciding which log to open first.
What it cannot establish
It cannot correct clock skew, reconstruct missing ranks, prove temporal order across separate files, or diagnose an unseen signature. Use the complete pipeline when the evidence is split, incomplete or ambiguous.
Evidence to collect before naming a cause
Keep the first error from every available rank, its host and process identity, timestamps with clock context, the collective sequence, and the transport messages before the timeout. A missing rank or an unhandled system error needs more evidence. A printed rank label can also be wrong when a process participates in overlapping groups.
PyTorch documents how to compare per-rank Flight Recorder traces and stack snapshots in its Flight Recorder hang tutorial. This browser decoder does not import Flight Recorder trace files.
Need the repeatable rank-by-rank method?
Use the task guide to collect, normalize, classify and verify the first failed rank.
Open the first-rank guidePrefer to continue in your editor? Try the free VS Code extension. If your team has a resolved incident to evaluate, request a Team evaluation.