/debug

description: Diagnose why a ComfyUI workflow failed
argument-hint: prompt_id or "last" to debug the most recent execution

/comfy-debug — Diagnose a Failed Workflow

The user wants to find out why a ComfyUI workflow execution failed and get a suggested fix.

Instructions

1. **Get the execution history.** The argument is: $ARGUMENTS

• If a prompt_id is provided, call `get_history(action="list")` with that prompt_id
• If "last" is provided or no argument given, call `get_history(action="list")` with no prompt_id to get the most recent execution

2. **Extract the error.** From the history response, identify:

• `node_id`: the node where execution failed
• `node_type` / `class_type`: what kind of node it was
• `exception_message`: the error message
• `traceback`: the full Python traceback

If the execution succeeded (no error), tell the user it completed normally and show the output summary.

3. **Get relevant logs.** Call `get_system_stats (action:"logs")` with a `keyword` filter matching the error. Use the exception class name (e.g., "RuntimeError", "ValueError") or a distinctive phrase from the error message. Request up to 200 lines.

4. **Inspect the failing node.** Call `create_workflow (action:"node_info")` with the `node_type` of the failing node. Check:

• What inputs does the node expect?
• Are there required inputs that might be missing or mistyped?
• What data types are expected for each input?

5. **Check for missing models.** If the error mentions a missing file, model, or checkpoint:

• Call `list_local_models` to see what's installed
• Compare against what the workflow references
• If a model is missing, suggest using `download_model` `action:"download"` or provide a search query for `action:"search"`

6. **Check for missing nodes.** If the error is a `KeyError` or mentions an unknown node type:

• The node pack may not be installed
• Call `search_custom_nodes` (`action: "search"`) with the node class name as `query` to find which pack provides it
• Suggest installing the pack

7. **Present the diagnosis.** Provide a summary:

• **What failed**: node type, node ID, and a one-line description
• **Why it failed**: root cause explanation in plain language
• **Suggested fix**: concrete steps the user can take to resolve the issue
• **Traceback excerpt**: the most relevant lines from the traceback (not the full dump)

Common Failure Patterns

• **OOM / CUDA out of memory**: Suggest reducing resolution, using FP8 models, or `clear_vram` before retrying
• **Missing checkpoint/model file**: Show what's installed, offer to download the right one
• **Missing custom node**: Identify the pack and suggest installation
• **Shape mismatch**: Usually a resolution or latent size issue; check that width/height are multiples of 8 (or 64 for some models)
• **NaN/Inf in tensor**: Model corruption or extreme CFG values; suggest re-downloading the model or lowering CFG
• **Connection type mismatch**: A node is receiving the wrong data type; check the workflow wiring

Example

User: `/comfy-debug last`

Steps:

• Call `get_history(action="list")` with no prompt_id
• Find error: node 12 (KSampler) threw RuntimeError "Expected all tensors to be on the same device"
• Call `get_system_stats (action:"logs")` with keyword "RuntimeError"
• Call `create_workflow (action:"node_info")` for "KSampler"
• Diagnose: model and conditioning are on different devices, likely a VRAM issue
• Suggest: restart ComfyUI or use `clear_vram` before retrying

Notes

• If multiple nodes errored, focus on the first failure in the execution chain; downstream errors usually cascade from it
• The traceback is Python-level; translate it into plain language for the user
• If the error is ambiguous, suggest the user share their workflow JSON for a closer look