ComfyUI prompt validation failed
Separate missing inputs and invalid selections from runtime exceptions.
Recognize the message
Prompt outputs failed validation; required input is missing; value not in list
Validation can reject a prompt before execution. The detailed report usually identifies a node and a specific missing input or disallowed widget value. It is different from a runtime sampler exception.
Work through the evidence
- Open Show report and note each node ID, class and rejected field. Preserve the UI export; API prompt format and visual UI workflow format are different.
- Check required sockets in the actual ComfyUI node definition. Connect the matching output type and replace stale dropdown selections with values offered by this installation.
- Use OnBeg’s checker to inspect exported references, then reopen the corrected copy in ComfyUI. Do not disable validation as a general fix for an invalid graph.
Verify the result
The prompt is accepted and execution begins. A later runtime error is new evidence; record it separately rather than assuming validation solved every issue.
What this does not prove
OnBeg’s structural checks cover references and graph evidence; they cannot validate every custom node’s dynamic inputs or prove your installed model choices.
Inspect before changing your workflow
The log inspector works in your browser. The workflow checker reads exported graph structure. Neither sends files automatically or executes nodes. Preserve the original, inspect a copy and record the actual test result in Casebook.
Inspect your log ↗ · Check the graph ↗ · Record a recovery case ↗Before asking for help
Include the first full exception, the failing stage, software versions, model family and the smallest reproducible graph. Redact API keys, user paths and private prompts. A summary such as “KSampler broken” removes the context that distinguishes one failure from another.
Prepare a redacted copy ↗Related investigations
ComfyUI CUDA out of memory · ComfyUI missing custom nodes · ComfyUI model not found · ComfyUI custom node import failed
Source and scope
These are OnBeg’s diagnostic checklists, informed by official ComfyUI troubleshooting. They are not universal fixes and do not replace model- or extension-specific instructions.