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ComfyUI is a node-based UI for Stable Diffusion and other image generation models. The MeiGen MCP plugin can connect to your local ComfyUI server, giving your AI assistant the ability to generate images on your own GPU — for free, with full privacy.

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Prerequisites

  • ComfyUI installed and running (installation guide)
  • At least one checkpoint model downloaded (e.g., SDXL, Flux, or Stable Diffusion 1.5)
  • The MeiGen MCP plugin installed (Setup Guide)
  • COMFYUI_URL configured (default: http://127.0.0.1:8188)

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Exporting a Workflow from ComfyUI

The plugin uses ComfyUI’s API format — a JSON file that describes the workflow as a graph of nodes. This is different from the standard ComfyUI save format.
1

Enable Dev Mode

In ComfyUI, go to Settings → enable Dev Mode Options. This adds the API format save button to the menu.
2

Build or load your workflow

Set up the workflow you want to use — choose your checkpoint, sampler, prompt nodes, and any other processing steps.
3

Save as API format

Click Save (API Format) in the menu. This exports a .json file in the node-graph format the plugin expects.
The regular Save button exports a different format that the plugin cannot use. You must use Save (API Format).

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Importing Workflows

After exporting from ComfyUI, import the workflow into the plugin: 
comfyui_workflow import ~/path/to/my-workflow.json
The plugin will:
  1. Parse the workflow JSON
  2. Auto-detect key nodes:
    • KSampler — sampler, steps, CFG, scheduler
    • CLIPTextEncode — positive and negative prompt
    • EmptyLatentImage — image width and height
    • CheckpointLoader — model checkpoint
    • LoadImage — reference image input
    • SaveImage — output node
  3. Save the template to ~/.config/meigen/workflows/
  4. Report which nodes were detected and which parameters can be controlled
You can import multiple workflows and switch between them when generating.

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Managing Workflows

Use the comfyui_workflow tool to manage your imported templates:
ActionDescription
listShow all imported workflows with a summary (model, sampler, steps)
viewInspect a workflow’s full node graph, parameters, and editable fields
modifyChange workflow parameters — steps, CFG, sampler, scheduler, checkpoint, etc.
deleteRemove a workflow template

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Viewing a Workflow

comfyui_workflow view my-workflow
Shows all nodes with their parameters. Editable nodes (prompt, sampler, size, model) are highlighted so the AI assistant knows what it can change.

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Modifying Parameters

comfyui_workflow modify my-workflow --node "3" --input "steps" --value "30"
Changes are saved to the template file. The original ComfyUI workflow is not affected.

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How Generation Works

When you ask the AI to generate an image using ComfyUI:
  1. Prompt injection — your prompt text is inserted into the positive CLIPTextEncode node
  2. Size calculation — the requested aspect ratio is converted to pixel dimensions (rounded to multiples of 8 for Stable Diffusion compatibility)
  3. Reference images — if you provided reference image URLs, the plugin downloads them and uploads to ComfyUI’s input/ directory, then injects them into LoadImage nodes
  4. Workflow submission — the modified workflow is submitted to ComfyUI’s API
  5. Status polling — the plugin polls every 2 seconds until generation completes (5-minute timeout)
  6. Result retrieval — the generated image is downloaded from ComfyUI and returned

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Reference Images

To use reference images with ComfyUI, your workflow must include at least one LoadImage node.
  • The plugin automatically detects LoadImage nodes in your workflow
  • When you provide reference image URLs, the plugin downloads and uploads them to ComfyUI
  • If your workflow has no LoadImage nodes, reference images are ignored (with a warning)
For image-to-image (img2img) workflows, make sure your workflow includes a LoadImage node connected to the appropriate processing chain. Standard text-to-image workflows typically don’t include this node.

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Performance Notes

AspectDetail
ConcurrencySerial only — one image at a time. Your local GPU can’t run multiple generations in parallel.
Timeout5 minutes maximum per generation
Poll interval2 seconds
Size roundingDimensions are rounded to multiples of 8 for Stable Diffusion compatibility

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Troubleshooting

ComfyUI is not running or the URL is wrong. Start ComfyUI and check that COMFYUI_URL matches the address shown in the ComfyUI terminal output (default: http://127.0.0.1:8188).
You need to import at least one workflow before generating. Export a workflow from ComfyUI using Save (API Format), then import it with comfyui_workflow import.
The plugin uses class-type matching to detect nodes. If detection fails for a custom node, use comfyui_workflow view to see all nodes, then comfyui_workflow modify to manually set parameters.
The workflow references a checkpoint model that isn’t downloaded. Check ComfyUI’s models/checkpoints/ directory and ensure the filename matches what the workflow expects.
Your workflow must include a LoadImage node. Standard text-to-image workflows don’t have this. Create or use an img2img workflow instead.